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* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.index;
import org.apache.logging.log4j.Logger;
import org.apache.lucene.index.MergePolicy;
import org.apache.lucene.index.NoMergePolicy;
import org.apache.lucene.index.TieredMergePolicy;
import org.elasticsearch.common.logging.DeprecationLogger;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.unit.ByteSizeUnit;
import org.elasticsearch.common.unit.ByteSizeValue;
/**
* 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 force merge 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
* force merge). 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 {
private final TieredMergePolicy mergePolicy = new TieredMergePolicy();
private final Logger logger;
private final boolean mergesEnabled;
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 Setting<Double> INDEX_COMPOUND_FORMAT_SETTING =
new Setting<>("index.compound_format", Double.toString(TieredMergePolicy.DEFAULT_NO_CFS_RATIO), MergePolicyConfig::parseNoCFSRatio,
Property.Dynamic, Property.IndexScope);
public static final Setting<Double> INDEX_MERGE_POLICY_EXPUNGE_DELETES_ALLOWED_SETTING =
Setting.doubleSetting("index.merge.policy.expunge_deletes_allowed", DEFAULT_EXPUNGE_DELETES_ALLOWED, 0.0d,
Property.Dynamic, Property.IndexScope);
public static final Setting<ByteSizeValue> INDEX_MERGE_POLICY_FLOOR_SEGMENT_SETTING =
Setting.byteSizeSetting("index.merge.policy.floor_segment", DEFAULT_FLOOR_SEGMENT,
Property.Dynamic, Property.IndexScope);
public static final Setting<Integer> INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_SETTING =
Setting.intSetting("index.merge.policy.max_merge_at_once", DEFAULT_MAX_MERGE_AT_ONCE, 2,
Property.Dynamic, Property.IndexScope);
public static final Setting<Integer> INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_EXPLICIT_SETTING =
Setting.intSetting("index.merge.policy.max_merge_at_once_explicit", DEFAULT_MAX_MERGE_AT_ONCE_EXPLICIT, 2,
Property.Dynamic, Property.IndexScope);
public static final Setting<ByteSizeValue> INDEX_MERGE_POLICY_MAX_MERGED_SEGMENT_SETTING =
Setting.byteSizeSetting("index.merge.policy.max_merged_segment", DEFAULT_MAX_MERGED_SEGMENT,
Property.Dynamic, Property.IndexScope);
public static final Setting<Double> INDEX_MERGE_POLICY_SEGMENTS_PER_TIER_SETTING =
Setting.doubleSetting("index.merge.policy.segments_per_tier", DEFAULT_SEGMENTS_PER_TIER, 2.0d,
Property.Dynamic, Property.IndexScope);
public static final Setting<Double> INDEX_MERGE_POLICY_RECLAIM_DELETES_WEIGHT_SETTING =
Setting.doubleSetting("index.merge.policy.reclaim_deletes_weight", DEFAULT_RECLAIM_DELETES_WEIGHT, 0.0d,
Property.Dynamic, Property.IndexScope);
public static final String INDEX_MERGE_ENABLED = "index.merge.enabled"; // don't convert to Setting<> and register... we only set this in tests and register via a plugin
MergePolicyConfig(Logger logger, IndexSettings indexSettings) {
this.logger = logger;
double forceMergeDeletesPctAllowed = indexSettings.getValue(INDEX_MERGE_POLICY_EXPUNGE_DELETES_ALLOWED_SETTING); // percentage
ByteSizeValue floorSegment = indexSettings.getValue(INDEX_MERGE_POLICY_FLOOR_SEGMENT_SETTING);
int maxMergeAtOnce = indexSettings.getValue(INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_SETTING);
int maxMergeAtOnceExplicit = indexSettings.getValue(INDEX_MERGE_POLICY_MAX_MERGE_AT_ONCE_EXPLICIT_SETTING);
// 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.getValue(INDEX_MERGE_POLICY_MAX_MERGED_SEGMENT_SETTING);
double segmentsPerTier = indexSettings.getValue(INDEX_MERGE_POLICY_SEGMENTS_PER_TIER_SETTING);
double reclaimDeletesWeight = indexSettings.getValue(INDEX_MERGE_POLICY_RECLAIM_DELETES_WEIGHT_SETTING);
this.mergesEnabled = indexSettings.getSettings()
.getAsBooleanLenientForPreEs6Indices(indexSettings.getIndexVersionCreated(), INDEX_MERGE_ENABLED, true, new DeprecationLogger(logger));
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(indexSettings.getValue(INDEX_COMPOUND_FORMAT_SETTING));
mergePolicy.setForceMergeDeletesPctAllowed(forceMergeDeletesPctAllowed);
mergePolicy.setFloorSegmentMB(floorSegment.getMbFrac());
mergePolicy.setMaxMergeAtOnce(maxMergeAtOnce);
mergePolicy.setMaxMergeAtOnceExplicit(maxMergeAtOnceExplicit);
mergePolicy.setMaxMergedSegmentMB(maxMergedSegment.getMbFrac());
mergePolicy.setSegmentsPerTier(segmentsPerTier);
mergePolicy.setReclaimDeletesWeight(reclaimDeletesWeight);
if (logger.isTraceEnabled()) {
logger.trace("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);
}
}
void setReclaimDeletesWeight(Double reclaimDeletesWeight) {
mergePolicy.setReclaimDeletesWeight(reclaimDeletesWeight);
}
void setSegmentsPerTier(Double segmentsPerTier) {
mergePolicy.setSegmentsPerTier(segmentsPerTier);
}
void setMaxMergedSegment(ByteSizeValue maxMergedSegment) {
mergePolicy.setMaxMergedSegmentMB(maxMergedSegment.getMbFrac());
}
void setMaxMergesAtOnceExplicit(Integer maxMergeAtOnceExplicit) {
mergePolicy.setMaxMergeAtOnceExplicit(maxMergeAtOnceExplicit);
}
void setMaxMergesAtOnce(Integer maxMergeAtOnce) {
mergePolicy.setMaxMergeAtOnce(maxMergeAtOnce);
}
void setFloorSegmentSetting(ByteSizeValue floorSegementSetting) {
mergePolicy.setFloorSegmentMB(floorSegementSetting.getMbFrac());
}
void setExpungeDeletesAllowed(Double value) {
mergePolicy.setForceMergeDeletesPctAllowed(value);
}
void setNoCFSRatio(Double noCFSRatio) {
mergePolicy.setNoCFSRatio(noCFSRatio);
}
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;
}
MergePolicy getMergePolicy() {
return mergesEnabled ? mergePolicy : NoMergePolicy.INSTANCE;
}
private 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);
}
}
}
}