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* 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
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*/
package org.elasticsearch.index.shard;
import org.apache.lucene.index.MergePolicy;
import org.apache.lucene.index.NoMergePolicy;
import org.apache.lucene.index.TieredMergePolicy;
import org.elasticsearch.common.logging.ESLogger;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.unit.ByteSizeUnit;
import org.elasticsearch.common.unit.ByteSizeValue;
import org.elasticsearch.index.settings.IndexSettingsService;
/**
* A shard in elasticsearch is a Lucene index, and a Lucene index is broken
* down into segments. Segments are internal storage elements in the index
* where the index data is stored, and are immutable up to delete markers.
* Segments are, periodically, merged into larger segments to keep the
* index size at bay and expunge deletes.
*
* <p>
* Merges select segments of approximately equal size, subject to an allowed
* number of segments per tier. The merge policy is able to merge
* non-adjacent segments, and separates how many segments are merged at once from how many
* segments are allowed per tier. It also does not over-merge (i.e., cascade merges).
*
* <p>
* All merge policy settings are <b>dynamic</b> and can be updated on a live index.
* The merge policy has the following settings:
*
* <ul>
* <li><code>index.merge.policy.expunge_deletes_allowed</code>:
*
* When expungeDeletes is called, we only merge away a segment if its delete
* percentage is over this threshold. Default is <code>10</code>.
*
* <li><code>index.merge.policy.floor_segment</code>:
*
* Segments smaller than this are "rounded up" to this size, i.e. treated as
* equal (floor) size for merge selection. This is to prevent frequent
* flushing of tiny segments, thus preventing a long tail in the index. Default
* is <code>2mb</code>.
*
* <li><code>index.merge.policy.max_merge_at_once</code>:
*
* Maximum number of segments to be merged at a time during "normal" merging.
* Default is <code>10</code>.
*
* <li><code>index.merge.policy.max_merge_at_once_explicit</code>:
*
* Maximum number of segments to be merged at a time, during optimize or
* expungeDeletes. Default is <code>30</code>.
*
* <li><code>index.merge.policy.max_merged_segment</code>:
*
* Maximum sized segment to produce during normal merging (not explicit
* optimize). This setting is approximate: the estimate of the merged segment
* size is made by summing sizes of to-be-merged segments (compensating for
* percent deleted docs). Default is <code>5gb</code>.
*
* <li><code>index.merge.policy.segments_per_tier</code>:
*
* Sets the allowed number of segments per tier. Smaller values mean more
* merging but fewer segments. Default is <code>10</code>. Note, this value needs to be
* >= than the <code>max_merge_at_once</code> otherwise you'll force too many merges to
* occur.
*
* <li><code>index.merge.policy.reclaim_deletes_weight</code>:
*
* Controls how aggressively merges that reclaim more deletions are favored.
* Higher values favor selecting merges that reclaim deletions. A value of
* <code>0.0</code> means deletions don't impact merge selection. Defaults to <code>2.0</code>.
* </ul>
*
* <p>
* For normal merging, the policy first computes a "budget" of how many
* segments are allowed to be in the index. If the index is over-budget,
* then the policy sorts segments by decreasing size (proportionally considering percent
* deletes), and then finds the least-cost merge. Merge cost is measured by
* a combination of the "skew" of the merge (size of largest seg divided by
* smallest seg), total merge size and pct deletes reclaimed, so that
* merges with lower skew, smaller size and those reclaiming more deletes,
* are favored.
*
* <p>
* If a merge will produce a segment that's larger than
* <code>max_merged_segment</code> then the policy will merge fewer segments (down to
* 1 at once, if that one has deletions) to keep the segment size under
* budget.
*
* <p>
* Note, this can mean that for large shards that holds many gigabytes of
* data, the default of <code>max_merged_segment</code> (<code>5gb</code>) can cause for many
* segments to be in an index, and causing searches to be slower. Use the
* indices segments API to see the segments that an index has, and
* possibly either increase the <code>max_merged_segment</code> or issue an optimize
* call for the index (try and aim to issue it on a low traffic time).
*/
public final class MergePolicyConfig implements IndexSettingsService.Listener{
private final TieredMergePolicy mergePolicy = new TieredMergePolicy();
private final ESLogger logger;
private final boolean mergesEnabled;
private volatile double noCFSRatio;
public static final double DEFAULT_EXPUNGE_DELETES_ALLOWED = 10d;
public static final ByteSizeValue DEFAULT_FLOOR_SEGMENT = new ByteSizeValue(2, ByteSizeUnit.MB);
public static final int DEFAULT_MAX_MERGE_AT_ONCE = 10;
public static final int DEFAULT_MAX_MERGE_AT_ONCE_EXPLICIT = 30;
public static final ByteSizeValue DEFAULT_MAX_MERGED_SEGMENT = new ByteSizeValue(5, ByteSizeUnit.GB);
public static final double DEFAULT_SEGMENTS_PER_TIER = 10.0d;
public static final double DEFAULT_RECLAIM_DELETES_WEIGHT = 2.0d;
public static final String INDEX_COMPOUND_FORMAT = "index.compound_format";
public static final String INDEX_MERGE_POLICY_EXPUNGE_DELETES_ALLOWED = "index.merge.policy.expunge_deletes_allowed";
public static final String INDEX_MERGE_POLICY_FLOOR_SEGMENT = "index.merge.policy.floor_segment";
public static final String INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE = "index.merge.policy.max_merge_at_once";
public static final String INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_EXPLICIT = "index.merge.policy.max_merge_at_once_explicit";
public static final String INDEX_MERGE_POLICY_MAX_MERGED_SEGMENT = "index.merge.policy.max_merged_segment";
public static final String INDEX_MERGE_POLICY_SEGMENTS_PER_TIER = "index.merge.policy.segments_per_tier";
public static final String INDEX_MERGE_POLICY_RECLAIM_DELETES_WEIGHT = "index.merge.policy.reclaim_deletes_weight";
public static final String INDEX_MERGE_ENABLED = "index.merge.enabled";
public MergePolicyConfig(ESLogger logger, Settings indexSettings) {
this.logger = logger;
this.noCFSRatio = parseNoCFSRatio(indexSettings.get(INDEX_COMPOUND_FORMAT, Double.toString(TieredMergePolicy.DEFAULT_NO_CFS_RATIO)));
double forceMergeDeletesPctAllowed = indexSettings.getAsDouble("index.merge.policy.expunge_deletes_allowed", DEFAULT_EXPUNGE_DELETES_ALLOWED); // percentage
ByteSizeValue floorSegment = indexSettings.getAsBytesSize("index.merge.policy.floor_segment", DEFAULT_FLOOR_SEGMENT);
int maxMergeAtOnce = indexSettings.getAsInt("index.merge.policy.max_merge_at_once", DEFAULT_MAX_MERGE_AT_ONCE);
int maxMergeAtOnceExplicit = indexSettings.getAsInt("index.merge.policy.max_merge_at_once_explicit", DEFAULT_MAX_MERGE_AT_ONCE_EXPLICIT);
// TODO is this really a good default number for max_merge_segment, what happens for large indices, won't they end up with many segments?
ByteSizeValue maxMergedSegment = indexSettings.getAsBytesSize("index.merge.policy.max_merged_segment", DEFAULT_MAX_MERGED_SEGMENT);
double segmentsPerTier = indexSettings.getAsDouble("index.merge.policy.segments_per_tier", DEFAULT_SEGMENTS_PER_TIER);
double reclaimDeletesWeight = indexSettings.getAsDouble("index.merge.policy.reclaim_deletes_weight", DEFAULT_RECLAIM_DELETES_WEIGHT);
this.mergesEnabled = indexSettings.getAsBoolean(INDEX_MERGE_ENABLED, true);
if (mergesEnabled == false) {
logger.warn("[{}] is set to false, this should only be used in tests and can cause serious problems in production environments", INDEX_MERGE_ENABLED);
}
maxMergeAtOnce = adjustMaxMergeAtOnceIfNeeded(maxMergeAtOnce, segmentsPerTier);
mergePolicy.setNoCFSRatio(noCFSRatio);
mergePolicy.setForceMergeDeletesPctAllowed(forceMergeDeletesPctAllowed);
mergePolicy.setFloorSegmentMB(floorSegment.mbFrac());
mergePolicy.setMaxMergeAtOnce(maxMergeAtOnce);
mergePolicy.setMaxMergeAtOnceExplicit(maxMergeAtOnceExplicit);
mergePolicy.setMaxMergedSegmentMB(maxMergedSegment.mbFrac());
mergePolicy.setSegmentsPerTier(segmentsPerTier);
mergePolicy.setReclaimDeletesWeight(reclaimDeletesWeight);
logger.debug("using [tiered] merge mergePolicy with expunge_deletes_allowed[{}], floor_segment[{}], max_merge_at_once[{}], max_merge_at_once_explicit[{}], max_merged_segment[{}], segments_per_tier[{}], reclaim_deletes_weight[{}]",
forceMergeDeletesPctAllowed, floorSegment, maxMergeAtOnce, maxMergeAtOnceExplicit, maxMergedSegment, segmentsPerTier, reclaimDeletesWeight);
}
private int adjustMaxMergeAtOnceIfNeeded(int maxMergeAtOnce, double segmentsPerTier) {
// fixing maxMergeAtOnce, see TieredMergePolicy#setMaxMergeAtOnce
if (!(segmentsPerTier >= maxMergeAtOnce)) {
int newMaxMergeAtOnce = (int) segmentsPerTier;
// max merge at once should be at least 2
if (newMaxMergeAtOnce <= 1) {
newMaxMergeAtOnce = 2;
}
logger.debug("changing max_merge_at_once from [{}] to [{}] because segments_per_tier [{}] has to be higher or equal to it", maxMergeAtOnce, newMaxMergeAtOnce, segmentsPerTier);
maxMergeAtOnce = newMaxMergeAtOnce;
}
return maxMergeAtOnce;
}
public MergePolicy getMergePolicy() {
return mergesEnabled ? mergePolicy : NoMergePolicy.INSTANCE;
}
@Override
public void onRefreshSettings(Settings settings) {
final double oldExpungeDeletesPctAllowed = mergePolicy.getForceMergeDeletesPctAllowed();
final double expungeDeletesPctAllowed = settings.getAsDouble(INDEX_MERGE_POLICY_EXPUNGE_DELETES_ALLOWED, oldExpungeDeletesPctAllowed);
if (expungeDeletesPctAllowed != oldExpungeDeletesPctAllowed) {
logger.info("updating [expunge_deletes_allowed] from [{}] to [{}]", oldExpungeDeletesPctAllowed, expungeDeletesPctAllowed);
mergePolicy.setForceMergeDeletesPctAllowed(expungeDeletesPctAllowed);
}
final double oldFloorSegmentMB = mergePolicy.getFloorSegmentMB();
final ByteSizeValue floorSegment = settings.getAsBytesSize(INDEX_MERGE_POLICY_FLOOR_SEGMENT, null);
if (floorSegment != null && floorSegment.mbFrac() != oldFloorSegmentMB) {
logger.info("updating [floor_segment] from [{}mb] to [{}]", oldFloorSegmentMB, floorSegment);
mergePolicy.setFloorSegmentMB(floorSegment.mbFrac());
}
final double oldSegmentsPerTier = mergePolicy.getSegmentsPerTier();
final double segmentsPerTier = settings.getAsDouble(INDEX_MERGE_POLICY_SEGMENTS_PER_TIER, oldSegmentsPerTier);
if (segmentsPerTier != oldSegmentsPerTier) {
logger.info("updating [segments_per_tier] from [{}] to [{}]", oldSegmentsPerTier, segmentsPerTier);
mergePolicy.setSegmentsPerTier(segmentsPerTier);
}
final int oldMaxMergeAtOnce = mergePolicy.getMaxMergeAtOnce();
int maxMergeAtOnce = settings.getAsInt(INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE, oldMaxMergeAtOnce);
if (maxMergeAtOnce != oldMaxMergeAtOnce) {
logger.info("updating [max_merge_at_once] from [{}] to [{}]", oldMaxMergeAtOnce, maxMergeAtOnce);
maxMergeAtOnce = adjustMaxMergeAtOnceIfNeeded(maxMergeAtOnce, segmentsPerTier);
mergePolicy.setMaxMergeAtOnce(maxMergeAtOnce);
}
final int oldMaxMergeAtOnceExplicit = mergePolicy.getMaxMergeAtOnceExplicit();
final int maxMergeAtOnceExplicit = settings.getAsInt(INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_EXPLICIT, oldMaxMergeAtOnceExplicit);
if (maxMergeAtOnceExplicit != oldMaxMergeAtOnceExplicit) {
logger.info("updating [max_merge_at_once_explicit] from [{}] to [{}]", oldMaxMergeAtOnceExplicit, maxMergeAtOnceExplicit);
mergePolicy.setMaxMergeAtOnceExplicit(maxMergeAtOnceExplicit);
}
final double oldMaxMergedSegmentMB = mergePolicy.getMaxMergedSegmentMB();
final ByteSizeValue maxMergedSegment = settings.getAsBytesSize(INDEX_MERGE_POLICY_MAX_MERGED_SEGMENT, null);
if (maxMergedSegment != null && maxMergedSegment.mbFrac() != oldMaxMergedSegmentMB) {
logger.info("updating [max_merged_segment] from [{}mb] to [{}]", oldMaxMergedSegmentMB, maxMergedSegment);
mergePolicy.setMaxMergedSegmentMB(maxMergedSegment.mbFrac());
}
final double oldReclaimDeletesWeight = mergePolicy.getReclaimDeletesWeight();
final double reclaimDeletesWeight = settings.getAsDouble(INDEX_MERGE_POLICY_RECLAIM_DELETES_WEIGHT, oldReclaimDeletesWeight);
if (reclaimDeletesWeight != oldReclaimDeletesWeight) {
logger.info("updating [reclaim_deletes_weight] from [{}] to [{}]", oldReclaimDeletesWeight, reclaimDeletesWeight);
mergePolicy.setReclaimDeletesWeight(reclaimDeletesWeight);
}
double noCFSRatio = parseNoCFSRatio(settings.get(INDEX_COMPOUND_FORMAT, Double.toString(MergePolicyConfig.this.noCFSRatio)));
if (noCFSRatio != MergePolicyConfig.this.noCFSRatio) {
logger.info("updating index.compound_format from [{}] to [{}]", formatNoCFSRatio(MergePolicyConfig.this.noCFSRatio), formatNoCFSRatio(noCFSRatio));
mergePolicy.setNoCFSRatio(noCFSRatio);
MergePolicyConfig.this.noCFSRatio = noCFSRatio;
}
}
public static double parseNoCFSRatio(String noCFSRatio) {
noCFSRatio = noCFSRatio.trim();
if (noCFSRatio.equalsIgnoreCase("true")) {
return 1.0d;
} else if (noCFSRatio.equalsIgnoreCase("false")) {
return 0.0;
} else {
try {
double value = Double.parseDouble(noCFSRatio);
if (value < 0.0 || value > 1.0) {
throw new IllegalArgumentException("NoCFSRatio must be in the interval [0..1] but was: [" + value + "]");
}
return value;
} catch (NumberFormatException ex) {
throw new IllegalArgumentException("Expected a boolean or a value in the interval [0..1] but was: [" + noCFSRatio + "]", ex);
}
}
}
public static String formatNoCFSRatio(double ratio) {
if (ratio == 1.0) {
return Boolean.TRUE.toString();
} else if (ratio == 0.0) {
return Boolean.FALSE.toString();
} else {
return Double.toString(ratio);
}
}
}