/*
* Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.mvstore;
import java.lang.Thread.UncaughtExceptionHandler;
import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;
import org.h2.compress.CompressDeflate;
import org.h2.compress.CompressLZF;
import org.h2.compress.Compressor;
import org.h2.mvstore.Page.PageChildren;
import org.h2.mvstore.cache.CacheLongKeyLIRS;
import org.h2.mvstore.type.StringDataType;
import org.h2.util.MathUtils;
import org.h2.util.New;
/*
TODO:
Documentation
- rolling docs review: at "Metadata Map"
- better document that writes are in background thread
- better document how to do non-unique indexes
- document pluggable store and OffHeapStore
TransactionStore:
- ability to disable the transaction log,
if there is only one connection
MVStore:
- better and clearer memory usage accounting rules
(heap memory versus disk memory), so that even there is
never an out of memory
even for a small heap, and so that chunks
are still relatively big on average
- make sure serialization / deserialization errors don't corrupt the file
- test and possibly improve compact operation (for large dbs)
- automated 'kill process' and 'power failure' test
- defragment (re-creating maps, specially those with small pages)
- store number of write operations per page (maybe defragment
if much different than count)
- r-tree: nearest neighbor search
- use a small object value cache (StringCache), test on Android
for default serialization
- MVStoreTool.dump should dump the data if possible;
possibly using a callback for serialization
- implement a sharded map (in one store, multiple stores)
to support concurrent updates and writes, and very large maps
- to save space when persisting very small transactions,
use a transaction log where only the deltas are stored
- serialization for lists, sets, sets, sorted sets, maps, sorted maps
- maybe rename 'rollback' to 'revert' to distinguish from transactions
- support other compression algorithms (deflate, LZ4,...)
- remove features that are not really needed; simplify the code
possibly using a separate layer or tools
(retainVersion?)
- optional pluggable checksum mechanism (per page), which
requires that everything is a page (including headers)
- rename "store" to "save", as "store" is used in "storeVersion"
- rename setStoreVersion to setDataVersion, setSchemaVersion or similar
- temporary file storage
- simple rollback method (rollback to last committed version)
- MVMap to implement SortedMap, then NavigableMap
- storage that splits database into multiple files,
to speed up compact and allow using trim
(by truncating / deleting empty files)
- add new feature to the file system API to avoid copying data
(reads that returns a ByteBuffer instead of writing into one)
for memory mapped files and off-heap storage
- support log structured merge style operations (blind writes)
using one map per level plus bloom filter
- have a strict call order MVStore -> MVMap -> Page -> FileStore
- autocommit commits, stores, and compacts from time to time;
the background thread should wait at least 90% of the
configured write delay to store changes
- compact* should also store uncommitted changes (if there are any)
- write a LSM-tree (log structured merge tree) utility on top of the MVStore
with blind writes and/or a bloom filter that
internally uses regular maps and merge sort
- chunk metadata: maybe split into static and variable,
or use a small page size for metadata
- data type "string": maybe use prefix compression for keys
- test chunk id rollover
- feature to auto-compact from time to time and on close
- compact very small chunks
- Page: to save memory, combine keys & values into one array
(also children & counts). Maybe remove some other
fields (childrenCount for example)
- Support SortedMap for MVMap
- compact: copy whole pages (without having to open all maps)
- maybe change the length code to have lower gaps
- test with very low limits (such as: short chunks, small pages)
- maybe allow to read beyond the retention time:
when compacting, move live pages in old chunks
to a map (possibly the metadata map) -
this requires a change in the compaction code, plus
a map lookup when reading old data; also, this
old data map needs to be cleaned up somehow;
maybe using an additional timeout
- rollback of removeMap should restore the data -
which has big consequences, as the metadata map
would probably need references to the root nodes of all maps
*/
/**
* A persistent storage for maps.
*/
public class MVStore {
/**
* Whether assertions are enabled.
*/
public static final boolean ASSERT = false;
/**
* The block size (physical sector size) of the disk. The store header is
* written twice, one copy in each block, to ensure it survives a crash.
*/
static final int BLOCK_SIZE = 4 * 1024;
private static final int FORMAT_WRITE = 1;
private static final int FORMAT_READ = 1;
/**
* Used to mark a chunk as free, when it was detected that live bookkeeping
* is incorrect.
*/
private static final int MARKED_FREE = 10000000;
/**
* The background thread, if any.
*/
volatile BackgroundWriterThread backgroundWriterThread;
private volatile boolean reuseSpace = true;
private boolean closed;
private FileStore fileStore;
private boolean fileStoreIsProvided;
private final int pageSplitSize;
/**
* The page cache. The default size is 16 MB, and the average size is 2 KB.
* It is split in 16 segments. The stack move distance is 2% of the expected
* number of entries.
*/
private CacheLongKeyLIRS<Page> cache;
/**
* The page chunk references cache. The default size is 4 MB, and the
* average size is 2 KB. It is split in 16 segments. The stack move distance
* is 2% of the expected number of entries.
*/
private CacheLongKeyLIRS<PageChildren> cacheChunkRef;
/**
* The newest chunk. If nothing was stored yet, this field is not set.
*/
private Chunk lastChunk;
/**
* The map of chunks.
*/
private final ConcurrentHashMap<Integer, Chunk> chunks =
new ConcurrentHashMap<Integer, Chunk>();
/**
* The map of temporarily freed storage space caused by freed pages. The key
* is the unsaved version, the value is the map of chunks. The maps contains
* the number of freed entries per chunk. Access is synchronized.
*/
private final ConcurrentHashMap<Long,
HashMap<Integer, Chunk>> freedPageSpace =
new ConcurrentHashMap<Long, HashMap<Integer, Chunk>>();
/**
* The metadata map. Write access to this map needs to be synchronized on
* the store.
*/
private MVMap<String, String> meta;
private final ConcurrentHashMap<Integer, MVMap<?, ?>> maps =
new ConcurrentHashMap<Integer, MVMap<?, ?>>();
private HashMap<String, Object> storeHeader = New.hashMap();
private WriteBuffer writeBuffer;
private int lastMapId;
private int versionsToKeep = 5;
/**
* The compression level for new pages (0 for disabled, 1 for fast, 2 for
* high). Even if disabled, the store may contain (old) compressed pages.
*/
private final int compressionLevel;
private Compressor compressorFast;
private Compressor compressorHigh;
private final UncaughtExceptionHandler backgroundExceptionHandler;
private long currentVersion;
/**
* The version of the last stored chunk, or -1 if nothing was stored so far.
*/
private long lastStoredVersion;
/**
* The estimated memory used by unsaved pages. This number is not accurate,
* also because it may be changed concurrently, and because temporary pages
* are counted.
*/
private int unsavedMemory;
private int autoCommitMemory;
private boolean saveNeeded;
/**
* The time the store was created, in milliseconds since 1970.
*/
private long creationTime;
/**
* How long to retain old, persisted chunks, in milliseconds. For larger or
* equal to zero, a chunk is never directly overwritten if unused, but
* instead, the unused field is set. If smaller zero, chunks are directly
* overwritten if unused.
*/
private int retentionTime;
private long lastCommitTime; //存放与creationTime的差值
/**
* The earliest chunk to retain, if any.
*/
private Chunk retainChunk; //目前没有用处
/**
* The version of the current store operation (if any).
*/
private volatile long currentStoreVersion = -1;
private Thread currentStoreThread;
private volatile boolean metaChanged;
/**
* The delay in milliseconds to automatically commit and write changes.
*/
private int autoCommitDelay;
private int autoCompactFillRate;
private long autoCompactLastFileOpCount;
private Object compactSync = new Object();
private IllegalStateException panicException;
private long lastTimeAbsolute;
private long lastFreeUnusedChunks;
/**
* Create and open the store.
*
* @param config the configuration to use
* @throws IllegalStateException if the file is corrupt, or an exception
* occurred while opening
* @throws IllegalArgumentException if the directory does not exist
*/
MVStore(HashMap<String, Object> config) {
Object o = config.get("compress");
this.compressionLevel = o == null ? 0 : (Integer) o;
String fileName = (String) config.get("fileName");
o = config.get("pageSplitSize");
if (o == null) {
pageSplitSize = fileName == null ? 4 * 1024 : 16 * 1024;
} else {
pageSplitSize = (Integer) o;
}
o = config.get("backgroundExceptionHandler");
this.backgroundExceptionHandler = (UncaughtExceptionHandler) o;
meta = new MVMap<String, String>(StringDataType.INSTANCE,
StringDataType.INSTANCE);
HashMap<String, Object> c = New.hashMap();
c.put("id", 0);
c.put("createVersion", currentVersion);
meta.init(this, c);
fileStore = (FileStore) config.get("fileStore");
if (fileName == null && fileStore == null) {
cache = null;
cacheChunkRef = null;
return;
}
if (fileStore == null) {
fileStoreIsProvided = false;
fileStore = new FileStore();
} else {
fileStoreIsProvided = true;
}
retentionTime = fileStore.getDefaultRetentionTime();
boolean readOnly = config.containsKey("readOnly");
o = config.get("cacheSize");
int mb = o == null ? 16 : (Integer) o;
if (mb > 0) {
CacheLongKeyLIRS.Config cc = new CacheLongKeyLIRS.Config();
cc.maxMemory = mb * 1024L * 1024L;
o = config.get("cacheConcurrency");
if (o != null) {
cc.segmentCount = (Integer) o;
}
cache = new CacheLongKeyLIRS<Page>(cc);
cc.maxMemory /= 4;
cacheChunkRef = new CacheLongKeyLIRS<PageChildren>(cc);
}
o = config.get("autoCommitBufferSize");
int kb = o == null ? 1024 : (Integer) o;
// 19 KB memory is about 1 KB storage
autoCommitMemory = kb * 1024 * 19;
o = config.get("autoCompactFillRate");
autoCompactFillRate = o == null ? 50 : (Integer) o;
char[] encryptionKey = (char[]) config.get("encryptionKey");
try {
if (!fileStoreIsProvided) {
fileStore.open(fileName, readOnly, encryptionKey);
}
if (fileStore.size() == 0) {
creationTime = getTimeAbsolute();
lastCommitTime = creationTime;
storeHeader.put("H", 2);
storeHeader.put("blockSize", BLOCK_SIZE);
storeHeader.put("format", FORMAT_WRITE);
storeHeader.put("created", creationTime);
writeStoreHeader();
} else {
readStoreHeader();
}
} catch (IllegalStateException e) {
panic(e);
} finally {
if (encryptionKey != null) {
Arrays.fill(encryptionKey, (char) 0);
}
}
lastCommitTime = getTimeSinceCreation();
// setAutoCommitDelay starts the thread, but only if
// the parameter is different from the old value
o = config.get("autoCommitDelay");
int delay = o == null ? 1000 : (Integer) o;
setAutoCommitDelay(delay);
}
private void panic(IllegalStateException e) {
if (backgroundExceptionHandler != null) {
backgroundExceptionHandler.uncaughtException(null, e);
}
panicException = e;
closeImmediately();
throw e;
}
/**
* Open a store in exclusive mode. For a file-based store, the parent
* directory must already exist.
*
* @param fileName the file name (null for in-memory)
* @return the store
*/
public static MVStore open(String fileName) {
HashMap<String, Object> config = New.hashMap();
config.put("fileName", fileName);
return new MVStore(config);
}
/**
* Open an old, stored version of a map.
*
* @param version the version
* @param mapId the map id
* @param template the template map
* @return the read-only map
*/
@SuppressWarnings("unchecked")
<T extends MVMap<?, ?>> T openMapVersion(long version, int mapId,
MVMap<?, ?> template) {
MVMap<String, String> oldMeta = getMetaMap(version);
long rootPos = getRootPos(oldMeta, mapId);
MVMap<?, ?> m = template.openReadOnly();
m.setRootPos(rootPos, version);
return (T) m;
}
/**
* Open a map with the default settings. The map is automatically create if
* it does not yet exist. If a map with this name is already open, this map
* is returned.
*
* @param <K> the key type
* @param <V> the value type
* @param name the name of the map
* @return the map
*/
public <K, V> MVMap<K, V> openMap(String name) {
return openMap(name, new MVMap.Builder<K, V>());
}
/**
* Open a map with the given builder. The map is automatically create if it
* does not yet exist. If a map with this name is already open, this map is
* returned.
*
* @param <K> the key type
* @param <V> the value type
* @param name the name of the map
* @param builder the map builder
* @return the map
*/
public synchronized <M extends MVMap<K, V>, K, V> M openMap(
String name, MVMap.MapBuilder<M, K, V> builder) {
checkOpen();
String x = meta.get("name." + name);
int id;
long root;
HashMap<String, Object> c;
M map;
if (x != null) {
id = DataUtils.parseHexInt(x);
@SuppressWarnings("unchecked")
M old = (M) maps.get(id);
if (old != null) {
return old;
}
map = builder.create();
String config = meta.get(MVMap.getMapKey(id));
c = New.hashMap();
c.putAll(DataUtils.parseMap(config));
c.put("id", id);
map.init(this, c);
root = getRootPos(meta, id);
} else {
c = New.hashMap();
id = ++lastMapId;
c.put("id", id);
c.put("createVersion", currentVersion);
map = builder.create();
map.init(this, c);
markMetaChanged();
x = Integer.toHexString(id);
meta.put(MVMap.getMapKey(id), map.asString(name));
meta.put("name." + name, x);
root = 0;
}
map.setRootPos(root, -1);
maps.put(id, map);
return map;
}
/**
* Get the set of all map names.
*
* @return the set of names
*/
public synchronized Set<String> getMapNames() {
HashSet<String> set = New.hashSet();
checkOpen();
for (Iterator<String> it = meta.keyIterator("name."); it.hasNext();) {
String x = it.next();
if (!x.startsWith("name.")) {
break;
}
set.add(x.substring("name.".length()));
}
return set;
}
/**
* Get the metadata map. This data is for informational purposes only. The
* data is subject to change in future versions.
* <p>
* The data in this map should not be modified (changing system data may
* corrupt the store). If modifications are needed, they need be
* synchronized on the store.
* <p>
* The metadata map contains the following entries:
* <pre>
* chunk.{chunkId} = {chunk metadata}
* name.{name} = {mapId}
* map.{mapId} = {map metadata}
* root.{mapId} = {root position}
* setting.storeVersion = {version}
* </pre>
*
* @return the metadata map
*/
public MVMap<String, String> getMetaMap() {
checkOpen();
return meta;
}
private MVMap<String, String> getMetaMap(long version) {
Chunk c = getChunkForVersion(version);
DataUtils.checkArgument(c != null, "Unknown version {0}", version);
c = readChunkHeader(c.block);
MVMap<String, String> oldMeta = meta.openReadOnly();
oldMeta.setRootPos(c.metaRootPos, version);
return oldMeta;
}
private Chunk getChunkForVersion(long version) {
Chunk newest = null;
for (Chunk c : chunks.values()) {
if (c.version <= version) {
if (newest == null || c.id > newest.id) {
newest = c;
}
}
}
return newest;
}
/**
* Check whether a given map exists.
*
* @param name the map name
* @return true if it exists
*/
public boolean hasMap(String name) {
return meta.containsKey("name." + name);
}
private void markMetaChanged() {
// changes in the metadata alone are usually not detected, as the meta
// map is changed after storing
metaChanged = true;
}
private synchronized void readStoreHeader() {
Chunk newest = null;
boolean validStoreHeader = false;
// find out which chunk and version are the newest
// read the first two blocks
ByteBuffer fileHeaderBlocks = fileStore.readFully(0, 2 * BLOCK_SIZE);
byte[] buff = new byte[BLOCK_SIZE];
for (int i = 0; i <= BLOCK_SIZE; i += BLOCK_SIZE) {
fileHeaderBlocks.get(buff);
// the following can fail for various reasons
try {
String s = new String(buff, 0, BLOCK_SIZE,
DataUtils.LATIN).trim();
HashMap<String, String> m = DataUtils.parseMap(s);
int blockSize = DataUtils.readHexInt(
m, "blockSize", BLOCK_SIZE);
if (blockSize != BLOCK_SIZE) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_UNSUPPORTED_FORMAT,
"Block size {0} is currently not supported",
blockSize);
}
int check = DataUtils.readHexInt(m, "fletcher", 0);
m.remove("fletcher");
s = s.substring(0, s.lastIndexOf("fletcher") - 1);
byte[] bytes = s.getBytes(DataUtils.LATIN);
int checksum = DataUtils.getFletcher32(bytes,
bytes.length);
if (check != checksum) {
continue;
}
long version = DataUtils.readHexLong(m, "version", 0);
if (newest == null || version > newest.version) {
validStoreHeader = true;
storeHeader.putAll(m);
creationTime = DataUtils.readHexLong(m, "created", 0);
int chunkId = DataUtils.readHexInt(m, "chunk", 0);
long block = DataUtils.readHexLong(m, "block", 0);
Chunk test = readChunkHeaderAndFooter(block);
if (test != null && test.id == chunkId) {
newest = test;
}
}
} catch (Exception e) {
continue;
}
}
if (!validStoreHeader) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Store header is corrupt: {0}", fileStore);
}
long format = DataUtils.readHexLong(storeHeader, "format", 1);
if (format > FORMAT_WRITE && !fileStore.isReadOnly()) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_UNSUPPORTED_FORMAT,
"The write format {0} is larger " +
"than the supported format {1}, " +
"and the file was not opened in read-only mode",
format, FORMAT_WRITE);
}
format = DataUtils.readHexLong(storeHeader, "formatRead", format); //"formatRead"目前未使用
if (format > FORMAT_READ) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_UNSUPPORTED_FORMAT,
"The read format {0} is larger " +
"than the supported format {1}",
format, FORMAT_READ);
}
lastStoredVersion = -1;
chunks.clear();
long now = System.currentTimeMillis();
// calculate the year (doesn't have to be exact;
// we assume 365.25 days per year, * 4 = 1461)
int year = 1970 + (int) (now / (1000L * 60 * 60 * 6 * 1461));
if (year < 2014) {
// if the year is before 2014,
// we assume the system doesn't have a real-time clock,
// and we set the creationTime to the past, so that
// existing chunks are overwritten
creationTime = now - fileStore.getDefaultRetentionTime();
} else if (now < creationTime) {
// the system time was set to the past:
// we change the creation time
creationTime = now;
storeHeader.put("created", creationTime);
}
Chunk test = readChunkFooter(fileStore.size());
if (test != null) {
test = readChunkHeaderAndFooter(test.block);
if (test != null) {
if (newest == null || test.version > newest.version) {
newest = test;
}
}
}
if (newest == null) {
// no chunk
return;
}
// read the chunk header and footer,
// and follow the chain of next chunks
while (true) {
if (newest.next == 0 ||
newest.next >= fileStore.size() / BLOCK_SIZE) {
// no (valid) next
break;
}
test = readChunkHeaderAndFooter(newest.next);
if (test == null || test.id <= newest.id) {
break;
}
newest = test;
}
setLastChunk(newest);
loadChunkMeta();
// read all chunk headers and footers within the retention time,
// to detect unwritten data after a power failure
verifyLastChunks();
// build the free space list
for (Chunk c : chunks.values()) {
if (c.pageCountLive == 0) {
// remove this chunk in the next save operation
registerFreePage(currentVersion, c.id, 0, 0);
}
long start = c.block * BLOCK_SIZE;
int length = c.len * BLOCK_SIZE;
fileStore.markUsed(start, length);
}
}
private void loadChunkMeta() {
// load the chunk metadata: we can load in any order,
// because loading chunk metadata might recursively load another chunk
for (Iterator<String> it = meta.keyIterator("chunk."); it.hasNext();) {
String s = it.next();
if (!s.startsWith("chunk.")) {
break;
}
s = meta.get(s);
Chunk c = Chunk.fromString(s);
if (!chunks.containsKey(c.id)) {
if (c.block == Long.MAX_VALUE) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Chunk {0} is invalid", c.id);
}
chunks.put(c.id, c);
}
}
}
private void setLastChunk(Chunk last) {
lastChunk = last;
if (last == null) {
// no valid chunk
lastMapId = 0;
currentVersion = 0;
meta.setRootPos(0, -1);
} else {
lastMapId = last.mapId;
currentVersion = last.version;
chunks.put(last.id, last);
meta.setRootPos(last.metaRootPos, -1);
}
setWriteVersion(currentVersion);
}
private void verifyLastChunks() {
long time = getTimeSinceCreation();
ArrayList<Integer> ids = new ArrayList<Integer>(chunks.keySet());
Collections.sort(ids);
int newestValidChunk = -1;
Chunk old = null;
for (Integer chunkId : ids) {
Chunk c = chunks.get(chunkId);
if (old != null && c.time < old.time) {
// old chunk (maybe leftover from a previous crash)
break;
}
old = c;
if (c.time + retentionTime < time) {
// old chunk, no need to verify
newestValidChunk = c.id;
continue;
}
Chunk test = readChunkHeaderAndFooter(c.block);
if (test == null || test.id != c.id) {
break;
}
newestValidChunk = chunkId;
}
Chunk newest = chunks.get(newestValidChunk);
if (newest != lastChunk) {
// to avoid re-using newer chunks later on, we could clear
// the headers and footers of those, but we might not know about all
// of them, so that could be incomplete - but we check that newer
// chunks are written after older chunks, so we are safe
rollbackTo(newest == null ? 0 : newest.version);
}
}
/**
* Read a chunk header and footer, and verify the stored data is consistent.
*
* @param block the block
* @return the chunk, or null if the header or footer don't match or are not
* consistent
*/
private Chunk readChunkHeaderAndFooter(long block) {
Chunk header;
try {
header = readChunkHeader(block);
} catch (Exception e) {
// invalid chunk header: ignore, but stop
return null;
}
if (header == null) {
return null;
}
Chunk footer = readChunkFooter((block + header.len) * BLOCK_SIZE);
if (footer == null || footer.id != header.id) {
return null;
}
return header;
}
/**
* Try to read a chunk footer.
*
* @param end the end of the chunk
* @return the chunk, or null if not successful
*/
private Chunk readChunkFooter(long end) {
// the following can fail for various reasons
try {
// read the chunk footer of the last block of the file
ByteBuffer lastBlock = fileStore.readFully(
end - Chunk.FOOTER_LENGTH, Chunk.FOOTER_LENGTH);
byte[] buff = new byte[Chunk.FOOTER_LENGTH];
lastBlock.get(buff);
String s = new String(buff, DataUtils.LATIN).trim();
HashMap<String, String> m = DataUtils.parseMap(s);
int check = DataUtils.readHexInt(m, "fletcher", 0);
m.remove("fletcher");
s = s.substring(0, s.lastIndexOf("fletcher") - 1);
byte[] bytes = s.getBytes(DataUtils.LATIN);
int checksum = DataUtils.getFletcher32(bytes, bytes.length);
if (check == checksum) {
int chunk = DataUtils.readHexInt(m, "chunk", 0);
Chunk c = new Chunk(chunk);
c.version = DataUtils.readHexLong(m, "version", 0);
c.block = DataUtils.readHexLong(m, "block", 0);
return c;
}
} catch (Exception e) {
// ignore
}
return null;
}
private void writeStoreHeader() {
StringBuilder buff = new StringBuilder();
if (lastChunk != null) {
storeHeader.put("block", lastChunk.block);
storeHeader.put("chunk", lastChunk.id);
storeHeader.put("version", lastChunk.version);
}
DataUtils.appendMap(buff, storeHeader);
byte[] bytes = buff.toString().getBytes(DataUtils.LATIN);
int checksum = DataUtils.getFletcher32(bytes, bytes.length);
DataUtils.appendMap(buff, "fletcher", checksum);
buff.append("\n");
bytes = buff.toString().getBytes(DataUtils.LATIN);
ByteBuffer header = ByteBuffer.allocate(2 * BLOCK_SIZE);
header.put(bytes);
header.position(BLOCK_SIZE);
header.put(bytes);
header.rewind();
write(0, header);
}
private void write(long pos, ByteBuffer buffer) {
try {
fileStore.writeFully(pos, buffer);
} catch (IllegalStateException e) {
panic(e);
throw e;
}
}
/**
* Close the file and the store. Unsaved changes are written to disk first.
*/
public void close() {
if (closed) {
return;
}
FileStore f = fileStore;
if (f != null && !f.isReadOnly()) {
stopBackgroundThread();
if (hasUnsavedChanges()) {
commitAndSave();
}
}
closeStore(true);
}
/**
* Close the file and the store, without writing anything. This will stop
* the background thread. This method ignores all errors.
*/
public void closeImmediately() {
try {
closeStore(false);
} catch (Exception e) {
if (backgroundExceptionHandler != null) {
backgroundExceptionHandler.uncaughtException(null, e);
}
}
}
private void closeStore(boolean shrinkIfPossible) {
if (closed) {
return;
}
// can not synchronize on this yet, because
// the thread also synchronized on this, which
// could result in a deadlock
stopBackgroundThread();
closed = true;
synchronized (this) {
if (fileStore != null && shrinkIfPossible) {
shrinkFileIfPossible(0);
}
// release memory early - this is important when called
// because of out of memory
cache = null;
cacheChunkRef = null;
for (MVMap<?, ?> m : New.arrayList(maps.values())) {
m.close();
}
meta = null;
chunks.clear();
maps.clear();
if (fileStore != null) {
try {
if (!fileStoreIsProvided) {
fileStore.close();
}
} finally {
fileStore = null;
}
}
}
}
/**
* Whether the chunk at the given position is live.
*
* @param chunkId the chunk id
* @return true if it is live
*/
boolean isChunkLive(int chunkId) {
String s = meta.get(Chunk.getMetaKey(chunkId));
return s != null;
}
/**
* Get the chunk for the given position.
*
* @param pos the position
* @return the chunk
*/
private Chunk getChunk(long pos) {
Chunk c = getChunkIfFound(pos);
if (c == null) {
int chunkId = DataUtils.getPageChunkId(pos);
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Chunk {0} not found", chunkId);
}
return c;
}
private Chunk getChunkIfFound(long pos) {
int chunkId = DataUtils.getPageChunkId(pos);
Chunk c = chunks.get(chunkId);
if (c == null) {
checkOpen();
if (!Thread.holdsLock(this)) {
// it could also be unsynchronized metadata
// access (if synchronization on this was forgotten)
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_CHUNK_NOT_FOUND,
"Chunk {0} no longer exists",
chunkId);
}
String s = meta.get(Chunk.getMetaKey(chunkId));
if (s == null) {
return null;
}
c = Chunk.fromString(s);
if (c.block == Long.MAX_VALUE) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Chunk {0} is invalid", chunkId);
}
chunks.put(c.id, c);
}
return c;
}
private void setWriteVersion(long version) {
for (MVMap<?, ?> map : maps.values()) {
map.setWriteVersion(version);
}
MVMap<String, String> m = meta;
if (m == null) {
checkOpen();
}
m.setWriteVersion(version);
}
/**
* Commit the changes.
* <p>
* For in-memory stores, this method increments the version.
* <p>
* For persistent stores, it also writes changes to disk. It does nothing if
* there are no unsaved changes, and returns the old version. It is not
* necessary to call this method when auto-commit is enabled (the default
* setting), as in this case it is automatically called from time to time or
* when enough changes have accumulated. However, it may still be called to
* flush all changes to disk.
*
* @return the new version
*/
public long commit() {
if (fileStore != null) {
return commitAndSave();
}
long v = ++currentVersion;
setWriteVersion(v);
return v;
}
/**
* Commit all changes and persist them to disk. This method does nothing if
* there are no unsaved changes, otherwise it increments the current version
* and stores the data (for file based stores).
* <p>
* At most one store operation may run at any time.
*
* @return the new version (incremented if there were changes)
*/
private synchronized long commitAndSave() {
if (closed) {
return currentVersion;
}
if (fileStore == null) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_WRITING_FAILED,
"This is an in-memory store");
}
if (currentStoreVersion >= 0) {
// store is possibly called within store, if the meta map changed
return currentVersion;
}
if (!hasUnsavedChanges()) {
return currentVersion;
}
if (fileStore.isReadOnly()) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_WRITING_FAILED, "This store is read-only");
}
try {
currentStoreVersion = currentVersion;
currentStoreThread = Thread.currentThread();
return storeNow();
} finally {
// in any case reset the current store version,
// to allow closing the store
currentStoreVersion = -1;
currentStoreThread = null;
}
}
private long storeNow() {
try {
return storeNowTry();
} catch (IllegalStateException e) {
panic(e);
return -1;
}
}
private long storeNowTry() {
long time = getTimeSinceCreation();
int freeDelay = retentionTime / 10;
if (time >= lastFreeUnusedChunks + freeDelay) {
// set early in case it fails (out of memory or so)
lastFreeUnusedChunks = time;
freeUnusedChunks();
// set it here as well, to avoid calling it often if it was slow
lastFreeUnusedChunks = getTimeSinceCreation();
}
int currentUnsavedPageCount = unsavedMemory;
long storeVersion = currentStoreVersion;
long version = ++currentVersion;
setWriteVersion(version);
lastCommitTime = time;
retainChunk = null;
// the metadata of the last chunk was not stored so far, and needs to be
// set now (it's better not to update right after storing, because that
// would modify the meta map again)
int lastChunkId;
if (lastChunk == null) {
lastChunkId = 0;
} else {
lastChunkId = lastChunk.id;
meta.put(Chunk.getMetaKey(lastChunkId), lastChunk.asString());
// never go backward in time
time = Math.max(lastChunk.time, time);
}
int newChunkId = lastChunkId;
while (true) {
newChunkId = (newChunkId + 1) % Chunk.MAX_ID;
Chunk old = chunks.get(newChunkId);
if (old == null) {
break;
}
if (old.block == Long.MAX_VALUE) {
IllegalStateException e = DataUtils.newIllegalStateException(
DataUtils.ERROR_INTERNAL,
"Last block not stored, possibly due to out-of-memory");
panic(e);
}
}
Chunk c = new Chunk(newChunkId);
c.pageCount = Integer.MAX_VALUE;
c.pageCountLive = Integer.MAX_VALUE;
c.maxLen = Long.MAX_VALUE;
c.maxLenLive = Long.MAX_VALUE;
c.metaRootPos = Long.MAX_VALUE;
c.block = Long.MAX_VALUE;
c.len = Integer.MAX_VALUE;
c.time = time;
c.version = version;
c.mapId = lastMapId;
c.next = Long.MAX_VALUE;
chunks.put(c.id, c);
// force a metadata update
meta.put(Chunk.getMetaKey(c.id), c.asString());
meta.remove(Chunk.getMetaKey(c.id));
ArrayList<MVMap<?, ?>> list = New.arrayList(maps.values());
ArrayList<MVMap<?, ?>> changed = New.arrayList();
for (MVMap<?, ?> m : list) {
m.setWriteVersion(version);
long v = m.getVersion();
if (m.getCreateVersion() > storeVersion) {
// the map was created after storing started
continue;
}
if (m.isVolatile()) {
continue;
}
if (v >= 0 && v >= lastStoredVersion) {
MVMap<?, ?> r = m.openVersion(storeVersion);
if (r.getRoot().getPos() == 0) {
changed.add(r);
}
}
}
applyFreedSpace(storeVersion);
WriteBuffer buff = getWriteBuffer();
// need to patch the header later
c.writeChunkHeader(buff, 0);
int headerLength = buff.position();
c.pageCount = 0;
c.pageCountLive = 0;
c.maxLen = 0;
c.maxLenLive = 0;
for (MVMap<?, ?> m : changed) {
Page p = m.getRoot();
String key = MVMap.getMapRootKey(m.getId());
if (p.getTotalCount() == 0) {
meta.put(key, "0");
} else {
p.writeUnsavedRecursive(c, buff);
long root = p.getPos();
meta.put(key, Long.toHexString(root));
}
}
meta.setWriteVersion(version);
Page metaRoot = meta.getRoot();
metaRoot.writeUnsavedRecursive(c, buff);
int chunkLength = buff.position();
// add the store header and round to the next block
int length = MathUtils.roundUpInt(chunkLength +
Chunk.FOOTER_LENGTH, BLOCK_SIZE);
buff.limit(length);
// the length of the file that is still in use
// (not necessarily the end of the file)
long end = getFileLengthInUse();
long filePos;
if (reuseSpace) {
filePos = fileStore.allocate(length);
} else {
filePos = end;
}
// end is not necessarily the end of the file
boolean storeAtEndOfFile = filePos + length >= fileStore.size();
if (!reuseSpace) {
// we can not mark it earlier, because it
// might have been allocated by one of the
// removed chunks
fileStore.markUsed(end, length);
}
c.block = filePos / BLOCK_SIZE;
c.len = length / BLOCK_SIZE;
c.metaRootPos = metaRoot.getPos();
// calculate and set the likely next position
if (reuseSpace) {
int predictBlocks = c.len;
long predictedNextStart = fileStore.allocate(
predictBlocks * BLOCK_SIZE);
fileStore.free(predictedNextStart, predictBlocks * BLOCK_SIZE);
c.next = predictedNextStart / BLOCK_SIZE;
} else {
// just after this chunk
c.next = 0;
}
buff.position(0);
c.writeChunkHeader(buff, headerLength);
revertTemp(storeVersion);
buff.position(buff.limit() - Chunk.FOOTER_LENGTH);
buff.put(c.getFooterBytes());
buff.position(0);
write(filePos, buff.getBuffer());
releaseWriteBuffer(buff);
// whether we need to write the store header
boolean writeStoreHeader = false;
if (!storeAtEndOfFile) {
if (lastChunk == null) {
writeStoreHeader = true;
} else if (lastChunk.next != c.block) {
// the last prediction did not matched
writeStoreHeader = true;
} else {
long headerVersion = DataUtils.readHexLong(
storeHeader, "version", 0);
if (lastChunk.version - headerVersion > 20) {
// we write after at least 20 entries
writeStoreHeader = true;
} else {
int chunkId = DataUtils.readHexInt(storeHeader, "chunk", 0);
while (true) {
Chunk old = chunks.get(chunkId);
if (old == null) {
// one of the chunks in between
// was removed
writeStoreHeader = true;
break;
}
if (chunkId == lastChunk.id) {
break;
}
chunkId++;
}
}
}
}
lastChunk = c;
if (writeStoreHeader) {
writeStoreHeader();
}
if (!storeAtEndOfFile) {
// may only shrink after the store header was written
shrinkFileIfPossible(1);
}
for (MVMap<?, ?> m : changed) {
Page p = m.getRoot();
if (p.getTotalCount() > 0) {
p.writeEnd();
}
}
metaRoot.writeEnd();
// some pages might have been changed in the meantime (in the newest
// version)
unsavedMemory = Math.max(0, unsavedMemory
- currentUnsavedPageCount);
metaChanged = false;
lastStoredVersion = storeVersion;
return version;
}
private synchronized void freeUnusedChunks() {
if (lastChunk == null || !reuseSpace) {
return;
}
Set<Integer> referenced = collectReferencedChunks();
ArrayList<Chunk> free = New.arrayList();
long time = getTimeSinceCreation();
for (Chunk c : chunks.values()) {
if (!referenced.contains(c.id)) {
free.add(c);
}
}
for (Chunk c : free) {
if (canOverwriteChunk(c, time)) {
chunks.remove(c.id);
markMetaChanged();
meta.remove(Chunk.getMetaKey(c.id));
long start = c.block * BLOCK_SIZE;
int length = c.len * BLOCK_SIZE;
fileStore.free(start, length);
} else {
if (c.unused == 0) {
c.unused = time;
meta.put(Chunk.getMetaKey(c.id), c.asString());
markMetaChanged();
}
}
}
}
private Set<Integer> collectReferencedChunks() {
long testVersion = lastChunk.version;
DataUtils.checkArgument(testVersion > 0, "Collect references on version 0");
long readCount = getFileStore().readCount; //多于的
Set<Integer> referenced = New.hashSet();
for (Cursor<String, String> c = meta.cursor("root."); c.hasNext();) {
String key = c.next();
if (!key.startsWith("root.")) {
break;
}
long pos = DataUtils.parseHexLong(c.getValue());
if (pos == 0) {
continue;
}
int mapId = DataUtils.parseHexInt(key.substring("root.".length()));
collectReferencedChunks(referenced, mapId, pos, 0);
}
long pos = lastChunk.metaRootPos;
collectReferencedChunks(referenced, 0, pos, 0);
readCount = fileStore.readCount - readCount; //多于的
return referenced;
}
private void collectReferencedChunks(Set<Integer> targetChunkSet,
int mapId, long pos, int level) { //level这个参数没用到
int c = DataUtils.getPageChunkId(pos);
targetChunkSet.add(c);
if (DataUtils.getPageType(pos) == DataUtils.PAGE_TYPE_LEAF) {
return;
}
PageChildren refs = readPageChunkReferences(mapId, pos, -1);
if (!refs.chunkList) {
Set<Integer> target = New.hashSet();
for (int i = 0; i < refs.children.length; i++) {
long p = refs.children[i];
collectReferencedChunks(target, mapId, p, level + 1);
}
// we don't need a reference to this chunk
target.remove(c);
long[] children = new long[target.size()];
int i = 0;
for (Integer p : target) {
children[i++] = DataUtils.getPagePos(p, 0, 0,
DataUtils.PAGE_TYPE_LEAF);
}
refs.children = children;
refs.chunkList = true;
if (cacheChunkRef != null) {
cacheChunkRef.put(refs.pos, refs, refs.getMemory());
}
}
for (long p : refs.children) {
targetChunkSet.add(DataUtils.getPageChunkId(p));
}
}
private PageChildren readPageChunkReferences(int mapId, long pos, int parentChunk) { //parentChunk这个参数目前都是-1
if (DataUtils.getPageType(pos) == DataUtils.PAGE_TYPE_LEAF) { //多于的
return null;
}
PageChildren r;
if (cacheChunkRef != null) {
r = cacheChunkRef.get(pos);
} else {
r = null;
}
if (r == null) {
// if possible, create it from the cached page
if (cache != null) {
Page p = cache.get(pos);
if (p != null) {
r = new PageChildren(p);
}
}
if (r == null) {
// page was not cached: read the data
Chunk c = getChunk(pos);
long filePos = c.block * BLOCK_SIZE;
filePos += DataUtils.getPageOffset(pos);
if (filePos < 0) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Negative position {0}; p={1}, c={2}", filePos, pos, c.toString());
}
long maxPos = (c.block + c.len) * BLOCK_SIZE;
r = PageChildren.read(fileStore, pos, mapId, filePos, maxPos);
}
r.removeDuplicateChunkReferences();
if (cacheChunkRef != null) {
cacheChunkRef.put(pos, r, r.getMemory());
}
}
if (r.children.length == 0) {
int chunk = DataUtils.getPageChunkId(pos);
if (chunk == parentChunk) { //多于的，逻辑也不对，若是返回null，前面那句if (!refs.chunkList)就抛出NPE
return null;
}
}
return r;
}
/**
* Get a buffer for writing. This caller must synchronize on the store
* before calling the method and until after using the buffer.
*
* @return the buffer
*/
private WriteBuffer getWriteBuffer() {
WriteBuffer buff;
if (writeBuffer != null) {
buff = writeBuffer;
buff.clear();
} else {
buff = new WriteBuffer();
}
return buff;
}
/**
* Release a buffer for writing. This caller must synchronize on the store
* before calling the method and until after using the buffer.
*
* @param buff the buffer than can be re-used
*/
private void releaseWriteBuffer(WriteBuffer buff) {
if (buff.capacity() <= 4 * 1024 * 1024) {
writeBuffer = buff;
}
}
private boolean canOverwriteChunk(Chunk c, long time) {
if (retentionTime >= 0) {
if (c.time + retentionTime > time) {
return false;
}
if (c.unused == 0 || c.unused + retentionTime / 2 > time) {
return false;
}
}
Chunk r = retainChunk; //retainChunk目前没有用处，是null
if (r != null && c.version > r.version) {
return false;
}
return true;
}
//creationTime是当前打开的xxx.mv.db文件的创建时间，这个方法就是返回从创建时间到现在经过的毫秒数
private long getTimeSinceCreation() {
return Math.max(0, getTimeAbsolute() - creationTime);
}
private long getTimeAbsolute() {
long now = System.currentTimeMillis();
if (lastTimeAbsolute != 0 && now < lastTimeAbsolute) {
// time seems to have run backwards - this can happen
// when the system time is adjusted, for example
// on a leap second
now = lastTimeAbsolute;
} else {
lastTimeAbsolute = now;
}
return now;
}
/**
* Apply the freed space to the chunk metadata. The metadata is updated, but
* completely free chunks are not removed from the set of chunks, and the
* disk space is not yet marked as free.
*
* @param storeVersion apply up to the given version
*/
private void applyFreedSpace(long storeVersion) {
while (true) {
ArrayList<Chunk> modified = New.arrayList();
Iterator<Entry<Long, HashMap<Integer, Chunk>>> it;
it = freedPageSpace.entrySet().iterator();
while (it.hasNext()) {
Entry<Long, HashMap<Integer, Chunk>> e = it.next();
long v = e.getKey();
if (v > storeVersion) {
continue;
}
HashMap<Integer, Chunk> freed = e.getValue();
for (Chunk f : freed.values()) {
Chunk c = chunks.get(f.id);
if (c == null) {
// already removed
continue;
}
// no need to synchronize, as old entries
// are not concurrently modified
c.maxLenLive += f.maxLenLive;
c.pageCountLive += f.pageCountLive;
if (c.pageCountLive < 0 && c.pageCountLive > -MARKED_FREE) {
// can happen after a rollback
c.pageCountLive = 0;
}
if (c.maxLenLive < 0 && c.maxLenLive > -MARKED_FREE) {
// can happen after a rollback
c.maxLenLive = 0;
}
modified.add(c);
}
it.remove();
}
for (Chunk c : modified) {
meta.put(Chunk.getMetaKey(c.id), c.asString());
}
if (modified.size() == 0) {
break;
}
}
}
/**
* Shrink the file if possible, and if at least a given percentage can be
* saved.
*
* @param minPercent the minimum percentage to save
*/
private void shrinkFileIfPossible(int minPercent) {
if (fileStore.isReadOnly()) {
return;
}
long end = getFileLengthInUse();
long fileSize = fileStore.size();
if (end >= fileSize) {
return;
}
if (minPercent > 0 && fileSize - end < BLOCK_SIZE) {
return;
}
int savedPercent = (int) (100 - (end * 100 / fileSize));
if (savedPercent < minPercent) {
return;
}
if (!closed) {
sync();
}
fileStore.truncate(end);
}
/**
* Get the position of the last used byte.
*
* @return the position
*/
private long getFileLengthInUse() {
long size = 2 * BLOCK_SIZE;
for (Chunk c : chunks.values()) {
if (c.len != Integer.MAX_VALUE) {
long x = (c.block + c.len) * BLOCK_SIZE;
size = Math.max(size, x);
}
}
return size;
}
/**
* Check whether there are any unsaved changes.
*
* @return if there are any changes
*/
public boolean hasUnsavedChanges() {
checkOpen();
if (metaChanged) {
return true;
}
for (MVMap<?, ?> m : maps.values()) {
if (!m.isClosed()) {
long v = m.getVersion();
if (v >= 0 && v > lastStoredVersion) {
return true;
}
}
}
return false;
}
private Chunk readChunkHeader(long block) {
long p = block * BLOCK_SIZE;
ByteBuffer buff = fileStore.readFully(p, Chunk.MAX_HEADER_LENGTH);
return Chunk.readChunkHeader(buff, p);
}
/**
* Compact the store by moving all live pages to new chunks.
*
* @return if anything was written
*/
public synchronized boolean compactRewriteFully() {
checkOpen();
if (lastChunk == null) {
// nothing to do
return false;
}
for (MVMap<?, ?> m : maps.values()) {
@SuppressWarnings("unchecked")
MVMap<Object, Object> map = (MVMap<Object, Object>) m;
Cursor<Object, Object> cursor = map.cursor(null);
Page lastPage = null;
while (cursor.hasNext()) {
cursor.next();
Page p = cursor.getPage();
if (p == lastPage) {
continue;
}
Object k = p.getKey(0);
Object v = p.getValue(0);
map.put(k, v);
lastPage = p;
}
}
commitAndSave();
return true;
}
/**
* Compact by moving all chunks next to each other.
*
* @return if anything was written
*/
public synchronized boolean compactMoveChunks() {
return compactMoveChunks(100, Long.MAX_VALUE);
}
/**
* Compact the store by moving all chunks next to each other, if there is
* free space between chunks. This might temporarily increase the file size.
* Chunks are overwritten irrespective of the current retention time. Before
* overwriting chunks and before resizing the file, syncFile() is called.
*
* @param targetFillRate do nothing if the file store fill rate is higher
* than this
* @param moveSize the number of bytes to move
* @return if anything was written
*/
public synchronized boolean compactMoveChunks(int targetFillRate, long moveSize) {
checkOpen();
if (lastChunk == null || !reuseSpace) {
// nothing to do
return false;
}
int oldRetentionTime = retentionTime;
boolean oldReuse = reuseSpace;
try {
retentionTime = -1;
freeUnusedChunks();
if (fileStore.getFillRate() > targetFillRate) {
return false;
}
long start = fileStore.getFirstFree() / BLOCK_SIZE;
ArrayList<Chunk> move = compactGetMoveBlocks(start, moveSize);
compactMoveChunks(move);
freeUnusedChunks();
storeNow();
} finally {
reuseSpace = oldReuse;
retentionTime = oldRetentionTime;
}
return true;
}
private ArrayList<Chunk> compactGetMoveBlocks(long startBlock, long moveSize) {
ArrayList<Chunk> move = New.arrayList();
for (Chunk c : chunks.values()) {
if (c.block > startBlock) {
move.add(c);
}
}
// sort by block
Collections.sort(move, new Comparator<Chunk>() {
@Override
public int compare(Chunk o1, Chunk o2) {
return Long.signum(o1.block - o2.block);
}
});
// find which is the last block to keep
int count = 0;
long size = 0;
for (Chunk c : move) {
long chunkSize = c.len * (long) BLOCK_SIZE;
if (size + chunkSize > moveSize) {
break;
}
size += chunkSize;
count++;
}
// move the first block (so the first gap is moved),
// and the one at the end (so the file shrinks)
while (move.size() > count && move.size() > 1) {
move.remove(1);
}
return move;
}
private void compactMoveChunks(ArrayList<Chunk> move) {
for (Chunk c : move) {
WriteBuffer buff = getWriteBuffer();
long start = c.block * BLOCK_SIZE;
int length = c.len * BLOCK_SIZE;
buff.limit(length);
ByteBuffer readBuff = fileStore.readFully(start, length);
Chunk.readChunkHeader(readBuff, start);
int chunkHeaderLen = readBuff.position();
buff.position(chunkHeaderLen);
buff.put(readBuff);
long end = getFileLengthInUse();
fileStore.markUsed(end, length);
fileStore.free(start, length);
c.block = end / BLOCK_SIZE;
c.next = 0;
buff.position(0);
c.writeChunkHeader(buff, chunkHeaderLen);
buff.position(length - Chunk.FOOTER_LENGTH);
buff.put(c.getFooterBytes());
buff.position(0);
write(end, buff.getBuffer());
releaseWriteBuffer(buff);
markMetaChanged();
meta.put(Chunk.getMetaKey(c.id), c.asString());
}
// update the metadata (store at the end of the file)
reuseSpace = false;
commitAndSave();
sync();
// now re-use the empty space
reuseSpace = true;
for (Chunk c : move) {
if (!chunks.containsKey(c.id)) {
// already removed during the
// previous store operation
continue;
}
WriteBuffer buff = getWriteBuffer();
long start = c.block * BLOCK_SIZE;
int length = c.len * BLOCK_SIZE;
buff.limit(length);
ByteBuffer readBuff = fileStore.readFully(start, length);
Chunk.readChunkHeader(readBuff, 0);
int chunkHeaderLen = readBuff.position();
buff.position(chunkHeaderLen);
buff.put(readBuff);
long pos = fileStore.allocate(length);
fileStore.free(start, length);
buff.position(0);
c.block = pos / BLOCK_SIZE;
c.writeChunkHeader(buff, chunkHeaderLen);
buff.position(length - Chunk.FOOTER_LENGTH);
buff.put(c.getFooterBytes());
buff.position(0);
write(pos, buff.getBuffer());
releaseWriteBuffer(buff);
markMetaChanged();
meta.put(Chunk.getMetaKey(c.id), c.asString());
}
// update the metadata (within the file)
commitAndSave();
sync();
shrinkFileIfPossible(0);
}
/**
* Force all stored changes to be written to the storage. The default
* implementation calls FileChannel.force(true).
*/
public void sync() {
checkOpen();
FileStore f = fileStore;
if (f != null) {
f.sync();
}
}
/**
* Try to increase the fill rate by re-writing partially full chunks. Chunks
* with a low number of live items are re-written.
* <p>
* If the current fill rate is higher than the target fill rate, nothing is
* done.
* <p>
* Please note this method will not necessarily reduce the file size, as
* empty chunks are not overwritten.
* <p>
* Only data of open maps can be moved. For maps that are not open, the old
* chunk is still referenced. Therefore, it is recommended to open all maps
* before calling this method.
*
* @param targetFillRate the minimum percentage of live entries
* @param write the minimum number of bytes to write
* @return if a chunk was re-written
*/
public boolean compact(int targetFillRate, int write) {
if (!reuseSpace) {
return false;
}
synchronized (compactSync) {
checkOpen();
ArrayList<Chunk> old;
synchronized (this) {
old = compactGetOldChunks(targetFillRate, write);
}
if (old == null || old.size() == 0) {
return false;
}
compactRewrite(old);
return true;
}
}
private ArrayList<Chunk> compactGetOldChunks(int targetFillRate, int write) {
if (lastChunk == null) {
// nothing to do
return null;
}
// calculate the fill rate
long maxLengthSum = 0;
long maxLengthLiveSum = 0;
long time = getTimeSinceCreation();
for (Chunk c : chunks.values()) {
// ignore young chunks, because we don't optimize those
if (c.time + retentionTime > time) { //retentionTime默认是45秒钟，见FileStore.getDefaultRetentionTime
continue;
}
maxLengthSum += c.maxLen;
maxLengthLiveSum += c.maxLenLive;
}
if (maxLengthLiveSum < 0) {
// no old data
return null;
}
// the fill rate of all chunks combined
if (maxLengthSum <= 0) {
// avoid division by 0
maxLengthSum = 1;
}
int fillRate = (int) (100 * maxLengthLiveSum / maxLengthSum);
if (fillRate >= targetFillRate) {
return null;
}
// the 'old' list contains the chunks we want to free up
ArrayList<Chunk> old = New.arrayList();
Chunk last = chunks.get(lastChunk.id);
for (Chunk c : chunks.values()) {
// only look at chunk older than the retention time
// (it's possible to compact chunks earlier, but right
// now we don't do that)
if (c.time + retentionTime > time) {
continue;
}
//年龄越小填充率越高优先级数字越大，移动collectPriority小的，也就是年龄大的填充率低的
long age = last.version - c.version + 1;
c.collectPriority = (int) (c.getFillRate() * 1000 / age);
old.add(c);
}
if (old.size() == 0) {
return null;
}
// sort the list, so the first entry should be collected first
Collections.sort(old, new Comparator<Chunk>() {
@Override
public int compare(Chunk o1, Chunk o2) { //collectPriority小的排在最前面，并且对排在前面的Chunk进行compact
int comp = new Integer(o1.collectPriority).
compareTo(o2.collectPriority);
if (comp == 0) {
comp = new Long(o1.maxLenLive).
compareTo(o2.maxLenLive);
}
return comp;
}
});
// find out up to were in the old list we need to move
long written = 0;
int chunkCount = 0;
Chunk move = null;
for (Chunk c : old) {
if (move != null) {
if (c.collectPriority > 0 && written > write) {
break;
}
}
written += c.maxLenLive;
chunkCount++;
move = c;
}
if (chunkCount < 1) {
return null;
}
// remove the chunks we want to keep from this list
boolean remove = false;
for (Iterator<Chunk> it = old.iterator(); it.hasNext();) {
Chunk c = it.next();
if (move == c) {
remove = true;
} else if (remove) {
it.remove();
}
}
return old;
}
private void compactRewrite(ArrayList<Chunk> old) {
HashSet<Integer> set = New.hashSet();
for (Chunk c : old) {
set.add(c.id);
}
for (MVMap<?, ?> m : maps.values()) {
@SuppressWarnings("unchecked")
MVMap<Object, Object> map = (MVMap<Object, Object>) m;
if (!map.rewrite(set)) {
return;
}
}
if (!meta.rewrite(set)) {
return;
}
freeUnusedChunks();
commitAndSave();
}
/**
* Read a page.
*
* @param map the map
* @param pos the page position
* @return the page
*/
Page readPage(MVMap<?, ?> map, long pos) {
if (pos == 0) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT, "Position 0");
}
Page p = cache == null ? null : cache.get(pos);
if (p == null) {
Chunk c = getChunk(pos);
long filePos = c.block * BLOCK_SIZE;
filePos += DataUtils.getPageOffset(pos);
if (filePos < 0) {
throw DataUtils.newIllegalStateException(
DataUtils.ERROR_FILE_CORRUPT,
"Negative position {0}", filePos);
}
long maxPos = (c.block + c.len) * BLOCK_SIZE;
p = Page.read(fileStore, pos, map, filePos, maxPos);
cachePage(pos, p, p.getMemory());
}
return p;
}
/**
* Remove a page.
*
* @param map the map the page belongs to
* @param pos the position of the page
* @param memory the memory usage
*/
void removePage(MVMap<?, ?> map, long pos, int memory) {
// we need to keep temporary pages,
// to support reading old versions and rollback
if (pos == 0) {
// the page was not yet stored:
// just using "unsavedMemory -= memory" could result in negative
// values, because in some cases a page is allocated, but never
// stored, so we need to use max
unsavedMemory = Math.max(0, unsavedMemory - memory);
return;
}
// This could result in a cache miss if the operation is rolled back,
// but we don't optimize for rollback.
// We could also keep the page in the cache, as somebody
// could still read it (reading the old version).
if (cache != null) {
if (DataUtils.getPageType(pos) == DataUtils.PAGE_TYPE_LEAF) {
// keep nodes in the cache, because they are still used for
// garbage collection
cache.remove(pos);
}
}
Chunk c = getChunk(pos);
long version = currentVersion;
if (map == meta && currentStoreVersion >= 0) {
if (Thread.currentThread() == currentStoreThread) {
// if the meta map is modified while storing,
// then this freed page needs to be registered
// with the stored chunk, so that the old chunk
// can be re-used
version = currentStoreVersion;
}
}
registerFreePage(version, c.id,
DataUtils.getPageMaxLength(pos), 1);
}
private void registerFreePage(long version, int chunkId,
long maxLengthLive, int pageCount) {
HashMap<Integer, Chunk> freed = freedPageSpace.get(version);
if (freed == null) {
freed = New.hashMap();
HashMap<Integer, Chunk> f2 = freedPageSpace.putIfAbsent(version,
freed);
if (f2 != null) {
freed = f2;
}
}
// synchronize, because pages could be freed concurrently
synchronized (freed) {
Chunk f = freed.get(chunkId);
if (f == null) {
f = new Chunk(chunkId);
freed.put(chunkId, f);
}
f.maxLenLive -= maxLengthLive;
f.pageCountLive -= pageCount;
}
}
Compressor getCompressorFast() {
if (compressorFast == null) {
compressorFast = new CompressLZF();
}
return compressorFast;
}
Compressor getCompressorHigh() {
if (compressorHigh == null) {
compressorHigh = new CompressDeflate();
}
return compressorHigh;
}
int getCompressionLevel() {
return compressionLevel;
}
public int getPageSplitSize() {
return pageSplitSize;
}
public boolean getReuseSpace() {
return reuseSpace;
}
/**
* Whether empty space in the file should be re-used. If enabled, old data
* is overwritten (default). If disabled, writes are appended at the end of
* the file.
* <p>
* This setting is specially useful for online backup. To create an online
* backup, disable this setting, then copy the file (starting at the
* beginning of the file). In this case, concurrent backup and write
* operations are possible (obviously the backup process needs to be faster
* than the write operations).
*
* @param reuseSpace the new value
*/
public void setReuseSpace(boolean reuseSpace) {
this.reuseSpace = reuseSpace;
}
public int getRetentionTime() {
return retentionTime;
}
/**
* How long to retain old, persisted chunks, in milliseconds. Chunks that
* are older may be overwritten once they contain no live data.
* <p>
* The default value is 45000 (45 seconds) when using the default file
* store. It is assumed that a file system and hard disk will flush all
* write buffers within this time. Using a lower value might be dangerous,
* unless the file system and hard disk flush the buffers earlier. To
* manually flush the buffers, use
* <code>MVStore.getFile().force(true)</code>, however please note that
* according to various tests this does not always work as expected
* depending on the operating system and hardware.
* <p>
* The retention time needs to be long enough to allow reading old chunks
* while traversing over the entries of a map.
* <p>
* This setting is not persisted.
*
* @param ms how many milliseconds to retain old chunks (0 to overwrite them
* as early as possible)
*/
public void setRetentionTime(int ms) {
this.retentionTime = ms;
}
/**
* How many versions to retain for in-memory stores. If not set, 5 old
* versions are retained.
*
* @param count the number of versions to keep
*/
public void setVersionsToKeep(int count) {
this.versionsToKeep = count;
}
/**
* Get the oldest version to retain in memory (for in-memory stores).
*
* @return the version
*/
public long getVersionsToKeep() {
return versionsToKeep;
}
/**
* Get the oldest version to retain in memory, which is the manually set
* retain version, or the current store version (whatever is older).
*
* @return the version
*/
long getOldestVersionToKeep() {
long v = currentVersion;
if (fileStore == null) {
return v - versionsToKeep;
}
long storeVersion = currentStoreVersion;
if (storeVersion > -1) {
v = Math.min(v, storeVersion);
}
return v;
}
/**
* Check whether all data can be read from this version. This requires that
* all chunks referenced by this version are still available (not
* overwritten).
*
* @param version the version
* @return true if all data can be read
*/
private boolean isKnownVersion(long version) {
if (version > currentVersion || version < 0) {
return false;
}
if (version == currentVersion || chunks.size() == 0) {
// no stored data
return true;
}
// need to check if a chunk for this version exists
Chunk c = getChunkForVersion(version);
if (c == null) {
return false;
}
// also, all chunks referenced by this version
// need to be available in the file
MVMap<String, String> oldMeta = getMetaMap(version);
if (oldMeta == null) {
return false;
}
try {
for (Iterator<String> it = oldMeta.keyIterator("chunk.");
it.hasNext();) {
String chunkKey = it.next();
if (!chunkKey.startsWith("chunk.")) {
break;
}
if (!meta.containsKey(chunkKey)) {
String s = oldMeta.get(chunkKey);
Chunk c2 = Chunk.fromString(s);
Chunk test = readChunkHeaderAndFooter(c2.block);
if (test == null || test.id != c2.id) {
return false;
}
// we store this chunk
chunks.put(c2.id, c2);
}
}
} catch (IllegalStateException e) {
// the chunk missing where the metadata is stored
return false;
}
return true;
}
/**
* Increment the number of unsaved pages.
*
* @param memory the memory usage of the page
*/
void registerUnsavedPage(int memory) {
unsavedMemory += memory;
int newValue = unsavedMemory;
if (newValue > autoCommitMemory && autoCommitMemory > 0) {
saveNeeded = true;
}
}
/**
* This method is called before writing to a map.
*
* @param map the map
*/
void beforeWrite(MVMap<?, ?> map) {
if (saveNeeded) {
if (map == meta) {
// to, don't save while the metadata map is locked
// this is to avoid deadlocks that could occur when we
// synchronize on the store and then on the metadata map
// TODO there should be no deadlocks possible
return;
}
saveNeeded = false;
// check again, because it could have been written by now
if (unsavedMemory > autoCommitMemory && autoCommitMemory > 0) {
commitAndSave();
}
}
}
/**
* Get the store version. The store version is usually used to upgrade the
* structure of the store after upgrading the application. Initially the
* store version is 0, until it is changed.
*
* @return the store version
*/
public int getStoreVersion() {
checkOpen();
String x = meta.get("setting.storeVersion");
return x == null ? 0 : DataUtils.parseHexInt(x);
}
/**
* Update the store version.
*
* @param version the new store version
*/
public synchronized void setStoreVersion(int version) {
checkOpen();
markMetaChanged();
meta.put("setting.storeVersion", Integer.toHexString(version));
}
/**
* Revert to the beginning of the current version, reverting all uncommitted
* changes.
*/
public void rollback() {
rollbackTo(currentVersion);
}
/**
* Revert to the beginning of the given version. All later changes (stored
* or not) are forgotten. All maps that were created later are closed. A
* rollback to a version before the last stored version is immediately
* persisted. Rollback to version 0 means all data is removed.
*
* @param version the version to revert to
*/
public synchronized void rollbackTo(long version) {
checkOpen();
if (version == 0) {
// special case: remove all data
for (MVMap<?, ?> m : maps.values()) {
m.close();
}
meta.clear();
chunks.clear();
if (fileStore != null) {
fileStore.clear();
}
maps.clear();
freedPageSpace.clear();
currentVersion = version;
setWriteVersion(version);
metaChanged = false;
return;
}
DataUtils.checkArgument(
isKnownVersion(version),
"Unknown version {0}", version);
for (MVMap<?, ?> m : maps.values()) {
m.rollbackTo(version);
}
for (long v = currentVersion; v >= version; v--) {
if (freedPageSpace.size() == 0) {
break;
}
freedPageSpace.remove(v);
}
meta.rollbackTo(version);
metaChanged = false;
boolean loadFromFile = false;
// find out which chunks to remove,
// and which is the newest chunk to keep
// (the chunk list can have gaps)
ArrayList<Integer> remove = new ArrayList<Integer>();
Chunk keep = null;
for (Chunk c : chunks.values()) {
if (c.version > version) {
remove.add(c.id);
} else if (keep == null || keep.id < c.id) {
keep = c;
}
}
if (remove.size() > 0) {
// remove the youngest first, so we don't create gaps
// (in case we remove many chunks)
Collections.sort(remove, Collections.reverseOrder());
revertTemp(version);
loadFromFile = true;
for (int id : remove) {
Chunk c = chunks.remove(id);
long start = c.block * BLOCK_SIZE;
int length = c.len * BLOCK_SIZE;
fileStore.free(start, length);
// overwrite the chunk,
// so it is not be used later on
WriteBuffer buff = getWriteBuffer();
buff.limit(length);
// buff.clear() does not set the data
Arrays.fill(buff.getBuffer().array(), (byte) 0);
write(start, buff.getBuffer());
releaseWriteBuffer(buff);
// only really needed if we remove many chunks, when writes are
// re-ordered - but we do it always, because rollback is not
// performance critical
sync();
}
lastChunk = keep;
writeStoreHeader();
readStoreHeader();
}
for (MVMap<?, ?> m : New.arrayList(maps.values())) {
int id = m.getId();
if (m.getCreateVersion() >= version) {
m.close();
maps.remove(id);
} else {
if (loadFromFile) {
m.setRootPos(getRootPos(meta, id), -1);
}
}
}
// rollback might have rolled back the stored chunk metadata as well
if (lastChunk != null) {
for (Chunk c : chunks.values()) {
meta.put(Chunk.getMetaKey(c.id), c.asString());
}
}
currentVersion = version;
setWriteVersion(version);
}
private static long getRootPos(MVMap<String, String> map, int mapId) {
String root = map.get(MVMap.getMapRootKey(mapId));
return root == null ? 0 : DataUtils.parseHexLong(root);
}
private void revertTemp(long storeVersion) {
for (Iterator<Long> it = freedPageSpace.keySet().iterator();
it.hasNext();) {
long v = it.next();
if (v > storeVersion) {
continue;
}
it.remove();
}
for (MVMap<?, ?> m : maps.values()) {
m.removeUnusedOldVersions();
}
}
/**
* Get the current version of the data. When a new store is created, the
* version is 0.
*
* @return the version
*/
public long getCurrentVersion() {
return currentVersion;
}
/**
* Get the file store.
*
* @return the file store
*/
public FileStore getFileStore() {
return fileStore;
}
/**
* Get the store header. This data is for informational purposes only. The
* data is subject to change in future versions. The data should not be
* modified (doing so may corrupt the store).
*
* @return the store header
*/
public Map<String, Object> getStoreHeader() {
return storeHeader;
}
private void checkOpen() {
if (closed) {
throw DataUtils.newIllegalStateException(DataUtils.ERROR_CLOSED,
"This store is closed", panicException);
}
}
/**
* Rename a map.
*
* @param map the map
* @param newName the new name
*/
public synchronized void renameMap(MVMap<?, ?> map, String newName) {
checkOpen();
DataUtils.checkArgument(map != meta,
"Renaming the meta map is not allowed");
int id = map.getId();
String oldName = getMapName(id);
if (oldName.equals(newName)) {
return;
}
DataUtils.checkArgument(
!meta.containsKey("name." + newName),
"A map named {0} already exists", newName);
markMetaChanged();
String x = Integer.toHexString(id);
meta.remove("name." + oldName);
meta.put(MVMap.getMapKey(id), map.asString(newName));
meta.put("name." + newName, x);
}
/**
* Remove a map. Please note rolling back this operation does not restore
* the data; if you need this ability, use Map.clear().
*
* @param map the map to remove
*/
public synchronized void removeMap(MVMap<?, ?> map) {
checkOpen();
DataUtils.checkArgument(map != meta,
"Removing the meta map is not allowed");
map.clear();
int id = map.getId();
String name = getMapName(id);
markMetaChanged();
meta.remove(MVMap.getMapKey(id));
meta.remove("name." + name);
meta.remove(MVMap.getMapRootKey(id));
maps.remove(id);
}
/**
* Get the name of the given map.
*
* @param id the map id
* @return the name, or null if not found
*/
public synchronized String getMapName(int id) {
checkOpen();
String m = meta.get(MVMap.getMapKey(id));
return m == null ? null : DataUtils.parseMap(m).get("name");
}
/**
* Commit and save all changes, if there are any, and compact the store if
* needed.
*/
void writeInBackground() {
if (closed) {
return;
}
// could also commit when there are many unsaved pages,
// but according to a test it doesn't really help
long time = getTimeSinceCreation();
if (time <= lastCommitTime + autoCommitDelay) {
return;
}
if (hasUnsavedChanges()) {
try {
commitAndSave();
} catch (Exception e) {
if (backgroundExceptionHandler != null) {
backgroundExceptionHandler.uncaughtException(null, e);
return;
}
}
}
if (autoCompactFillRate > 0) {
try {
// whether there were file read or write operations since
// the last time
boolean fileOps;
long fileOpCount = fileStore.getWriteCount() + fileStore.getReadCount();
if (autoCompactLastFileOpCount != fileOpCount) {
fileOps = true;
} else {
fileOps = false;
}
// use a lower fill rate if there were any file operations
int fillRate = fileOps ? autoCompactFillRate / 3 : autoCompactFillRate;
// TODO how to avoid endless compaction if there is a bug
// in the bookkeeping?
compact(fillRate, autoCommitMemory);
autoCompactLastFileOpCount = fileStore.getWriteCount() + fileStore.getReadCount();
} catch (Exception e) {
if (backgroundExceptionHandler != null) {
backgroundExceptionHandler.uncaughtException(null, e);
}
}
}
}
/**
* Set the read cache size in MB.
*
* @param mb the cache size in MB.
*/
public void setCacheSize(int mb) {
final long bytes = (long) mb * 1024 * 1024;
if (cache != null) {
cache.setMaxMemory(bytes);
cache.clear();
}
if (cacheChunkRef != null) {
cacheChunkRef.setMaxMemory(bytes / 4);
cacheChunkRef.clear();
}
}
public boolean isClosed() {
return closed;
}
private void stopBackgroundThread() {
BackgroundWriterThread t = backgroundWriterThread;
if (t == null) {
return;
}
backgroundWriterThread = null;
if (Thread.currentThread() == t) {
// within the thread itself - can not join
return;
}
synchronized (t.sync) {
t.sync.notifyAll();
}
if (Thread.holdsLock(this)) {
// called from storeNow: can not join,
// because that could result in a deadlock
return;
}
try {
t.join();
} catch (Exception e) {
// ignore
}
}
/**
* Set the maximum delay in milliseconds to auto-commit changes.
* <p>
* To disable auto-commit, set the value to 0. In this case, changes are
* only committed when explicitly calling commit.
* <p>
* The default is 1000, meaning all changes are committed after at most one
* second.
*
* @param millis the maximum delay
*/
public void setAutoCommitDelay(int millis) {
if (autoCommitDelay == millis) {
return;
}
autoCommitDelay = millis;
if (fileStore == null || fileStore.isReadOnly()) {
return;
}
stopBackgroundThread();
// start the background thread if needed
if (millis > 0) {
int sleep = Math.max(1, millis / 10);
BackgroundWriterThread t =
new BackgroundWriterThread(this, sleep,
fileStore.toString());
t.start();
backgroundWriterThread = t; //这行要放在t.start前，否则有可能t运行到run时，backgroundWriterThread还是null
}
}
/**
* Get the auto-commit delay.
*
* @return the delay in milliseconds, or 0 if auto-commit is disabled.
*/
public int getAutoCommitDelay() {
return autoCommitDelay;
}
/**
* Get the maximum memory (in bytes) used for unsaved pages. If this number
* is exceeded, unsaved changes are stored to disk.
*
* @return the memory in bytes
*/
public int getAutoCommitMemory() {
return autoCommitMemory;
}
/**
* Get the estimated memory (in bytes) of unsaved data. If the value exceeds
* the auto-commit memory, the changes are committed.
* <p>
* The returned value is an estimation only.
*
* @return the memory in bytes
*/
public int getUnsavedMemory() {
return unsavedMemory;
}
/**
* Put the page in the cache.
*
* @param pos the page position
* @param page the page
* @param memory the memory used
*/
void cachePage(long pos, Page page, int memory) {
if (cache != null) {
cache.put(pos, page, memory);
}
}
/**
* Get the amount of memory used for caching, in MB.
* Note that this does not include the page chunk references cache, which is
* 25% of the size of the page cache.
*
* @return the amount of memory used for caching
*/
public int getCacheSizeUsed() {
if (cache == null) {
return 0;
}
return (int) (cache.getUsedMemory() / 1024 / 1024);
}
/**
* Get the maximum cache size, in MB.
* Note that this does not include the page chunk references cache, which is
* 25% of the size of the page cache.
*
* @return the cache size
*/
public int getCacheSize() {
if (cache == null) {
return 0;
}
return (int) (cache.getMaxMemory() / 1024 / 1024);
}
/**
* Get the cache.
*
* @return the cache
*/
public CacheLongKeyLIRS<Page> getCache() {
return cache;
}
/**
* Whether the store is read-only.
*
* @return true if it is
*/
public boolean isReadOnly() {
return fileStore == null ? false : fileStore.isReadOnly();
}
/**
* A background writer thread to automatically store changes from time to
* time.
*/
private static class BackgroundWriterThread extends Thread {
public final Object sync = new Object();
private final MVStore store;
private final int sleep;
BackgroundWriterThread(MVStore store, int sleep, String fileStoreName) {
super("MVStore background writer " + fileStoreName);
this.store = store;
this.sleep = sleep;
setDaemon(true);
}
@Override
public void run() {
while (true) {
Thread t = store.backgroundWriterThread;
if (t == null) {
break;
}
synchronized (sync) {
try {
sync.wait(sleep); //在MVStore.stopBackgroundThread()中通知
} catch (InterruptedException e) {
continue;
}
}
store.writeInBackground();
}
}
}
/**
* A builder for an MVStore.
*/
public static class Builder {
private final HashMap<String, Object> config = New.hashMap();
private Builder set(String key, Object value) {
config.put(key, value);
return this;
}
/**
* Disable auto-commit, by setting the auto-commit delay and auto-commit
* buffer size to 0.
*
* @return this
*/
public Builder autoCommitDisabled() {
// we have a separate config option so that
// no thread is started if the write delay is 0
// (if we only had a setter in the MVStore,
// the thread would need to be started in any case)
set("autoCommitBufferSize", 0);
return set("autoCommitDelay", 0);
}
/**
* Set the size of the write buffer, in KB disk space (for file-based
* stores). Unless auto-commit is disabled, changes are automatically
* saved if there are more than this amount of changes.
* <p>
* The default is 1024 KB.
* <p>
* When the value is set to 0 or lower, data is not automatically
* stored.
*
* @param kb the write buffer size, in kilobytes
* @return this
*/
public Builder autoCommitBufferSize(int kb) {
return set("autoCommitBufferSize", kb);
}
/**
* Set the auto-compact target fill rate. If the average fill rate (the
* percentage of the storage space that contains active data) of the
* chunks is lower, then the chunks with a low fill rate are re-written.
* Also, if the percentage of empty space between chunks is higher than
* this value, then chunks at the end of the file are moved. Compaction
* stops if the target fill rate is reached.
* <p>
* The default value is 50 (50%). The value 0 disables auto-compacting.
* <p>
*
* @param percent the target fill rate
* @return this
*/
public Builder autoCompactFillRate(int percent) {
return set("autoCompactFillRate", percent);
}
/**
* Use the following file name. If the file does not exist, it is
* automatically created. The parent directory already must exist.
*
* @param fileName the file name
* @return this
*/
public Builder fileName(String fileName) {
return set("fileName", fileName);
}
/**
* Encrypt / decrypt the file using the given password. This method has
* no effect for in-memory stores. The password is passed as a
* char array so that it can be cleared as soon as possible. Please note
* there is still a small risk that password stays in memory (due to
* Java garbage collection). Also, the hashed encryption key is kept in
* memory as long as the file is open.
*
* @param password the password
* @return this
*/
public Builder encryptionKey(char[] password) {
return set("encryptionKey", password);
}
/**
* Open the file in read-only mode. In this case, a shared lock will be
* acquired to ensure the file is not concurrently opened in write mode.
* <p>
* If this option is not used, the file is locked exclusively.
* <p>
* Please note a store may only be opened once in every JVM (no matter
* whether it is opened in read-only or read-write mode), because each
* file may be locked only once in a process.
*
* @return this
*/
public Builder readOnly() {
return set("readOnly", 1);
}
/**
* Set the read cache size in MB. The default is 16 MB.
*
* @param mb the cache size in megabytes
* @return this
*/
public Builder cacheSize(int mb) {
return set("cacheSize", mb);
}
/**
* Set the read cache concurrency. The default is 16, meaning 16
* segments are used.
*
* @param concurrency the cache concurrency
* @return this
*/
public Builder cacheConcurrency(int concurrency) {
return set("cacheConcurrency", concurrency);
}
/**
* Compress data before writing using the LZF algorithm. This will save
* about 50% of the disk space, but will slow down read and write
* operations slightly.
* <p>
* This setting only affects writes; it is not necessary to enable
* compression when reading, even if compression was enabled when
* writing.
*
* @return this
*/
public Builder compress() {
return set("compress", 1);
}
/**
* Compress data before writing using the Deflate algorithm. This will
* save more disk space, but will slow down read and write operations
* quite a bit.
* <p>
* This setting only affects writes; it is not necessary to enable
* compression when reading, even if compression was enabled when
* writing.
*
* @return this
*/
public Builder compressHigh() {
return set("compress", 2);
}
/**
* Set the amount of memory a page should contain at most, in bytes,
* before it is split. The default is 16 KB for persistent stores and 4
* KB for in-memory stores. This is not a limit in the page size, as
* pages with one entry can get larger. It is just the point where pages
* that contain more than one entry are split.
*
* @param pageSplitSize the page size
* @return this
*/
public Builder pageSplitSize(int pageSplitSize) {
return set("pageSplitSize", pageSplitSize);
}
/**
* Set the listener to be used for exceptions that occur when writing in
* the background thread.
*
* @param exceptionHandler the handler
* @return this
*/
public Builder backgroundExceptionHandler(
Thread.UncaughtExceptionHandler exceptionHandler) {
return set("backgroundExceptionHandler", exceptionHandler);
}
/**
* Use the provided file store instead of the default one.
* <p>
* File stores passed in this way need to be open. They are not closed
* when closing the store.
* <p>
* Please note that any kind of store (including an off-heap store) is
* considered a "persistence", while an "in-memory store" means objects
* are not persisted and fully kept in the JVM heap.
*
* @param store the file store
* @return this
*/
public Builder fileStore(FileStore store) {
return set("fileStore", store);
}
/**
* Open the store.
*
* @return the opened store
*/
public MVStore open() {
return new MVStore(config);
}
@Override
public String toString() {
return DataUtils.appendMap(new StringBuilder(), config).toString();
}
/**
* Read the configuration from a string.
*
* @param s the string representation
* @return the builder
*/
public static Builder fromString(String s) {
HashMap<String, String> config = DataUtils.parseMap(s);
Builder builder = new Builder();
builder.config.putAll(config);
return builder;
}
}
}