/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.cassandra.db.rows;
import java.nio.ByteBuffer;
import java.util.Comparator;
import java.util.Iterator;
import org.apache.cassandra.schema.ColumnMetadata;
import org.apache.cassandra.db.Conflicts;
import org.apache.cassandra.db.DeletionTime;
import org.apache.cassandra.db.partitions.PartitionStatisticsCollector;
/**
* Static methods to work on cells.
*/
public abstract class Cells
{
private Cells() {}
/**
* Collect statistics ont a given cell.
*
* @param cell the cell for which to collect stats.
* @param collector the stats collector.
*/
public static void collectStats(Cell cell, PartitionStatisticsCollector collector)
{
collector.update(cell);
if (cell.isCounterCell())
collector.updateHasLegacyCounterShards(CounterCells.hasLegacyShards(cell));
}
/**
* Reconciles/merges two cells, one being an update to an existing cell,
* yielding index updates if appropriate.
* <p>
* Note that this method assumes that the provided cells can meaningfully
* be reconciled together, that is that those cells are for the same row and same
* column (and same cell path if the column is complex).
* <p>
* Also note that which cell is provided as {@code existing} and which is
* provided as {@code update} matters for index updates.
*
* @param existing the pre-existing cell, the one that is updated. This can be
* {@code null} if this reconciliation correspond to an insertion.
* @param update the newly added cell, the update. This can be {@code null} out
* of convenience, in which case this function simply copy {@code existing} to
* {@code writer}.
* @param deletion the deletion time that applies to the cells being considered.
* This deletion time may delete both {@code existing} or {@code update}.
* @param builder the row builder to which the result of the reconciliation is written.
* @param nowInSec the current time in seconds (which plays a role during reconciliation
* because deleted cells always have precedence on timestamp equality and deciding if a
* cell is a live or not depends on the current time due to expiring cells).
*
* @return the timestamp delta between existing and update, or {@code Long.MAX_VALUE} if one
* of them is {@code null} or deleted by {@code deletion}).
*/
public static long reconcile(Cell existing,
Cell update,
DeletionTime deletion,
Row.Builder builder,
int nowInSec)
{
existing = existing == null || deletion.deletes(existing) ? null : existing;
update = update == null || deletion.deletes(update) ? null : update;
if (existing == null || update == null)
{
if (update != null)
{
builder.addCell(update);
}
else if (existing != null)
{
builder.addCell(existing);
}
return Long.MAX_VALUE;
}
Cell reconciled = reconcile(existing, update, nowInSec);
builder.addCell(reconciled);
return Math.abs(existing.timestamp() - update.timestamp());
}
/**
* Reconciles/merge two cells.
* <p>
* Note that this method assumes that the provided cells can meaningfully
* be reconciled together, that is that cell are for the same row and same
* column (and same cell path if the column is complex).
* <p>
* This method is commutative over it's cells arguments: {@code reconcile(a, b, n) == reconcile(b, a, n)}.
*
* @param c1 the first cell participating in the reconciliation.
* @param c2 the second cell participating in the reconciliation.
* @param nowInSec the current time in seconds (which plays a role during reconciliation
* because deleted cells always have precedence on timestamp equality and deciding if a
* cell is a live or not depends on the current time due to expiring cells).
*
* @return a cell corresponding to the reconciliation of {@code c1} and {@code c2}.
* For non-counter cells, this will always be either {@code c1} or {@code c2}, but for
* counter cells this can be a newly allocated cell.
*/
public static Cell reconcile(Cell c1, Cell c2, int nowInSec)
{
if (c1 == null)
return c2 == null ? null : c2;
if (c2 == null)
return c1;
if (c1.isCounterCell() || c2.isCounterCell())
{
Conflicts.Resolution res = Conflicts.resolveCounter(c1.timestamp(),
c1.isLive(nowInSec),
c1.value(),
c2.timestamp(),
c2.isLive(nowInSec),
c2.value());
switch (res)
{
case LEFT_WINS: return c1;
case RIGHT_WINS: return c2;
default:
ByteBuffer merged = Conflicts.mergeCounterValues(c1.value(), c2.value());
long timestamp = Math.max(c1.timestamp(), c2.timestamp());
// We save allocating a new cell object if it turns out that one cell was
// a complete superset of the other
if (merged == c1.value() && timestamp == c1.timestamp())
return c1;
else if (merged == c2.value() && timestamp == c2.timestamp())
return c2;
else // merge clocks and timestamps.
return new BufferCell(c1.column(), timestamp, Cell.NO_TTL, Cell.NO_DELETION_TIME, merged, c1.path());
}
}
Conflicts.Resolution res = Conflicts.resolveRegular(c1.timestamp(),
c1.isLive(nowInSec),
c1.localDeletionTime(),
c1.value(),
c2.timestamp(),
c2.isLive(nowInSec),
c2.localDeletionTime(),
c2.value());
assert res != Conflicts.Resolution.MERGE;
return res == Conflicts.Resolution.LEFT_WINS ? c1 : c2;
}
/**
* Computes the reconciliation of a complex column given its pre-existing
* cells and the ones it is updated with, and generating index update if
* appropriate.
* <p>
* Note that this method assumes that the provided cells can meaningfully
* be reconciled together, that is that the cells are for the same row and same
* complex column.
* <p>
* Also note that which cells is provided as {@code existing} and which are
* provided as {@code update} matters for index updates.
*
* @param column the complex column the cells are for.
* @param existing the pre-existing cells, the ones that are updated. This can be
* {@code null} if this reconciliation correspond to an insertion.
* @param update the newly added cells, the update. This can be {@code null} out
* of convenience, in which case this function simply copy the cells from
* {@code existing} to {@code writer}.
* @param deletion the deletion time that applies to the cells being considered.
* This deletion time may delete cells in both {@code existing} and {@code update}.
* @param builder the row build to which the result of the reconciliation is written.
* @param nowInSec the current time in seconds (which plays a role during reconciliation
* because deleted cells always have precedence on timestamp equality and deciding if a
* cell is a live or not depends on the current time due to expiring cells).
*
* @return the smallest timestamp delta between corresponding cells from existing and update. A
* timestamp delta being computed as the difference between a cell from {@code update} and the
* cell in {@code existing} having the same cell path (if such cell exists). If the intersection
* of cells from {@code existing} and {@code update} having the same cell path is empty, this
* returns {@code Long.MAX_VALUE}.
*/
public static long reconcileComplex(ColumnMetadata column,
Iterator<Cell> existing,
Iterator<Cell> update,
DeletionTime deletion,
Row.Builder builder,
int nowInSec)
{
Comparator<CellPath> comparator = column.cellPathComparator();
Cell nextExisting = getNext(existing);
Cell nextUpdate = getNext(update);
long timeDelta = Long.MAX_VALUE;
while (nextExisting != null || nextUpdate != null)
{
int cmp = nextExisting == null ? 1
: (nextUpdate == null ? -1
: comparator.compare(nextExisting.path(), nextUpdate.path()));
if (cmp < 0)
{
reconcile(nextExisting, null, deletion, builder, nowInSec);
nextExisting = getNext(existing);
}
else if (cmp > 0)
{
reconcile(null, nextUpdate, deletion, builder, nowInSec);
nextUpdate = getNext(update);
}
else
{
timeDelta = Math.min(timeDelta, reconcile(nextExisting, nextUpdate, deletion, builder, nowInSec));
nextExisting = getNext(existing);
nextUpdate = getNext(update);
}
}
return timeDelta;
}
/**
* Adds to the builder a representation of the given existing cell that, when merged/reconciled with the given
* update cell, produces the same result as merging the original with the update.
* <p>
* For simple cells that is either the original cell (if still live), or nothing (if shadowed).
*
* @param existing the pre-existing cell, the one that is updated.
* @param update the newly added cell, the update. This can be {@code null} out
* of convenience, in which case this function simply copy {@code existing} to
* {@code writer}.
* @param deletion the deletion time that applies to the cells being considered.
* This deletion time may delete both {@code existing} or {@code update}.
* @param builder the row builder to which the result of the filtering is written.
* @param nowInSec the current time in seconds (which plays a role during reconciliation
* because deleted cells always have precedence on timestamp equality and deciding if a
* cell is a live or not depends on the current time due to expiring cells).
*/
public static void addNonShadowed(Cell existing,
Cell update,
DeletionTime deletion,
Row.Builder builder,
int nowInSec)
{
if (deletion.deletes(existing))
return;
Cell reconciled = reconcile(existing, update, nowInSec);
if (reconciled != update)
builder.addCell(existing);
}
/**
* Adds to the builder a representation of the given existing cell that, when merged/reconciled with the given
* update cell, produces the same result as merging the original with the update.
* <p>
* For simple cells that is either the original cell (if still live), or nothing (if shadowed).
*
* @param column the complex column the cells are for.
* @param existing the pre-existing cells, the ones that are updated.
* @param update the newly added cells, the update. This can be {@code null} out
* of convenience, in which case this function simply copy the cells from
* {@code existing} to {@code writer}.
* @param deletion the deletion time that applies to the cells being considered.
* This deletion time may delete both {@code existing} or {@code update}.
* @param builder the row builder to which the result of the filtering is written.
* @param nowInSec the current time in seconds (which plays a role during reconciliation
* because deleted cells always have precedence on timestamp equality and deciding if a
* cell is a live or not depends on the current time due to expiring cells).
*/
public static void addNonShadowedComplex(ColumnMetadata column,
Iterator<Cell> existing,
Iterator<Cell> update,
DeletionTime deletion,
Row.Builder builder,
int nowInSec)
{
Comparator<CellPath> comparator = column.cellPathComparator();
Cell nextExisting = getNext(existing);
Cell nextUpdate = getNext(update);
while (nextExisting != null)
{
int cmp = nextUpdate == null ? -1 : comparator.compare(nextExisting.path(), nextUpdate.path());
if (cmp < 0)
{
addNonShadowed(nextExisting, null, deletion, builder, nowInSec);
nextExisting = getNext(existing);
}
else if (cmp == 0)
{
addNonShadowed(nextExisting, nextUpdate, deletion, builder, nowInSec);
nextExisting = getNext(existing);
nextUpdate = getNext(update);
}
else
{
nextUpdate = getNext(update);
}
}
}
private static Cell getNext(Iterator<Cell> iterator)
{
return iterator == null || !iterator.hasNext() ? null : iterator.next();
}
}