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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* 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.engine;
import org.apache.lucene.document.LongPoint;
import org.apache.lucene.search.Query;
import org.elasticsearch.common.lease.Releasable;
import org.elasticsearch.index.mapper.SeqNoFieldMapper;
import org.elasticsearch.index.seqno.RetentionLease;
import org.elasticsearch.index.seqno.RetentionLeases;
import org.elasticsearch.index.seqno.SequenceNumbers;
import org.elasticsearch.index.translog.Translog;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.function.LongSupplier;
import java.util.function.Supplier;
/**
* A policy that controls how many soft-deleted documents should be retained for peer-recovery and querying history changes purpose.
*/
final class SoftDeletesPolicy {
private final LongSupplier globalCheckpointSupplier;
private long localCheckpointOfSafeCommit;
// This lock count is used to prevent `minRetainedSeqNo` from advancing.
private int retentionLockCount;
// The extra number of operations before the global checkpoint are retained
private long retentionOperations;
// The min seq_no value that is retained - ops after this seq# should exist in the Lucene index.
private long minRetainedSeqNo;
// provides the retention leases used to calculate the minimum sequence number to retain
private final Supplier retentionLeasesSupplier;
SoftDeletesPolicy(
final LongSupplier globalCheckpointSupplier,
final long minRetainedSeqNo,
final long retentionOperations,
final Supplier retentionLeasesSupplier) {
this.globalCheckpointSupplier = globalCheckpointSupplier;
this.retentionOperations = retentionOperations;
this.minRetainedSeqNo = minRetainedSeqNo;
this.retentionLeasesSupplier = Objects.requireNonNull(retentionLeasesSupplier);
this.localCheckpointOfSafeCommit = SequenceNumbers.NO_OPS_PERFORMED;
this.retentionLockCount = 0;
}
/**
* Updates the number of soft-deleted documents prior to the global checkpoint to be retained
* See {@link org.elasticsearch.index.IndexSettings#INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING}
*/
synchronized void setRetentionOperations(long retentionOperations) {
this.retentionOperations = retentionOperations;
}
/**
* Sets the local checkpoint of the current safe commit
*/
synchronized void setLocalCheckpointOfSafeCommit(long newCheckpoint) {
if (newCheckpoint < this.localCheckpointOfSafeCommit) {
throw new IllegalArgumentException("Local checkpoint can't go backwards; " +
"new checkpoint [" + newCheckpoint + "]," + "current checkpoint [" + localCheckpointOfSafeCommit + "]");
}
this.localCheckpointOfSafeCommit = newCheckpoint;
}
/**
* Acquires a lock on soft-deleted documents to prevent them from cleaning up in merge processes. This is necessary to
* make sure that all operations that are being retained will be retained until the lock is released.
* This is a analogy to the translog's retention lock; see {@link Translog#acquireRetentionLock()}
*/
synchronized Releasable acquireRetentionLock() {
assert retentionLockCount >= 0 : "Invalid number of retention locks [" + retentionLockCount + "]";
retentionLockCount++;
final AtomicBoolean released = new AtomicBoolean();
return () -> {
if (released.compareAndSet(false, true)) {
releaseRetentionLock();
}
};
}
private synchronized void releaseRetentionLock() {
assert retentionLockCount > 0 : "Invalid number of retention locks [" + retentionLockCount + "]";
retentionLockCount--;
}
/**
* Returns the min seqno that is retained in the Lucene index.
* Operations whose seq# is least this value should exist in the Lucene index.
*/
synchronized long getMinRetainedSeqNo() {
/*
* When an engine is flushed, we need to provide it the latest collection of retention leases even when the soft deletes policy is
* locked for peer recovery.
*/
final RetentionLeases retentionLeases = retentionLeasesSupplier.get();
// do not advance if the retention lock is held
if (retentionLockCount == 0) {
/*
* This policy retains operations for two purposes: peer-recovery and querying changes history.
* - Peer-recovery is driven by the local checkpoint of the safe commit. In peer-recovery, the primary transfers a safe commit,
* then sends operations after the local checkpoint of that commit. This requires keeping all ops after
* localCheckpointOfSafeCommit.
* - Changes APIs are driven by a combination of the global checkpoint, retention operations, and retention leases. Here we
* prefer using the global checkpoint instead of the maximum sequence number because only operations up to the global
* checkpoint are exposed in the changes APIs.
*/
// calculate the minimum sequence number to retain based on retention leases
final long minimumRetainingSequenceNumber = retentionLeases
.leases()
.stream()
.mapToLong(RetentionLease::retainingSequenceNumber)
.min()
.orElse(Long.MAX_VALUE);
/*
* The minimum sequence number to retain is the minimum of the minimum based on retention leases, and the number of operations
* below the global checkpoint to retain (index.soft_deletes.retention.operations). The additional increments on the global
* checkpoint and the local checkpoint of the safe commit are due to the fact that we want to retain all operations above
* those checkpoints.
*/
final long minSeqNoForQueryingChanges =
Math.min(1 + globalCheckpointSupplier.getAsLong() - retentionOperations, minimumRetainingSequenceNumber);
final long minSeqNoToRetain = Math.min(minSeqNoForQueryingChanges, 1 + localCheckpointOfSafeCommit);
/*
* We take the maximum as minSeqNoToRetain can go backward as the retention operations value can be changed in settings, or from
* the addition of leases with a retaining sequence number lower than previous retaining sequence numbers.
*/
minRetainedSeqNo = Math.max(minRetainedSeqNo, minSeqNoToRetain);
}
return minRetainedSeqNo;
}
/**
* Returns a soft-deletes retention query that will be used in {@link org.apache.lucene.index.SoftDeletesRetentionMergePolicy}
* Documents including tombstones are soft-deleted and matched this query will be retained and won't cleaned up by merges.
*/
Query getRetentionQuery() {
return LongPoint.newRangeQuery(SeqNoFieldMapper.NAME, getMinRetainedSeqNo(), Long.MAX_VALUE);
}
}