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https://issues.apache.org/jira/browse/HBASE-23591?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17012424#comment-17012424
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Anoop Sam John commented on HBASE-23591:
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So for the next time flush on the same CF what we encounter case is this
// This should not happen normally. However, lets be safe and guard against
these cases
// we received a flush commit with a larger seqId than what we have
prepared
// we will pick the flush file for this. We will also obtain the
updates lock and
// look for contents of the memstore to see whether we have edits
after this seqId.
// If not, we will drop all the memstore edits and the snapshot as
well.
We call
replayFlushInStores(flush, prepareFlushResult, true);
So the old snapshot will get cleared then. But at the replica memstore side the
actually flushed data (at this time) will be still in the memstore. Then again
when a prepare flush marker comes, it will take a snapshot in which those old
cells will also be included. So temp there will be extra data been kept at the
replica memstore.
But here there is a problem!
The first time flush case, we could not complete the replayFlushInStores. Means
we could not get the handles to the new flushed Hfile(s). That is ok because we
are keeping the snapshot there. So the data is still there in memory. But when
the second time flush comes and we do replayFlushInStores we will be knowing
the new flushed files only. And now we drop the snapshot also. Means we lost
ref to those data at the replica side. we will never get a chance to ref back
to the 1st time flushed file(s) as long as this replica region is not reopened.
Correct?
> Negative memStoreSizing
> -----------------------
>
> Key: HBASE-23591
> URL: https://issues.apache.org/jira/browse/HBASE-23591
> Project: HBase
> Issue Type: Bug
> Components: read replicas
> Reporter: Szabolcs Bukros
> Priority: Major
> Fix For: 2.2.2
>
>
> After a flush on the replica region the memStoreSizing becomes negative:
> {code:java}
> 2019-12-17 08:31:59,983 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Replaying flush marker action:
> COMMIT_FLUSH table_name: "IntegrationTestRegionReplicaReplicati
> on" encoded_region_name: "544affde3e027454f67c8ea46c8f69ee"
> flush_sequence_number: 41392 store_flushes { family_name: "f1"
> store_home_dir: "f1" flush_output: "3c48a23eac784a348a18e10e337d80a2" }
> store_flushes { family_name: "f2" store_home_dir: "f2" flush_output:
> "9a5283ec95694667b4ead2398af5f01e" } store_flushes { family_name: "f3"
> store_home_dir: "f3" flush_output: "e6f25e6b0eca4d22af15d0626d0f8759" }
> region_name:
> "IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697.544affde3e027454f67c8ea46c8f69ee."
> 2019-12-17 08:31:59,984 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Received a flush commit marker with
> seqId:41392 and a previous prepared snapshot was found
> 2019-12-17 08:31:59,993 INFO org.apache.hadoop.hbase.regionserver.HStore:
> Region: 0beaae111b0f6e98bfde31ba35be5408 added
> hdfs://replica-1:8020/hbase/data/default/IntegrationTestRegionReplicaReplication/544affde3e027454f67c8ea46c8f69ee/f1/3c48a23eac784a348a18e10e337d80a2,
> entries=32445, sequenceid=41392, filesize=27.6 M
> 2019-12-17 08:32:00,016 INFO org.apache.hadoop.hbase.regionserver.HStore:
> Region: 0beaae111b0f6e98bfde31ba35be5408 added
> hdfs://replica-1:8020/hbase/data/default/IntegrationTestRegionReplicaReplication/544affde3e027454f67c8ea46c8f69ee/f2/9a5283ec95694667b4ead2398af5f01e,
> entries=12264, sequenceid=41392, filesize=10.9 M
> 2019-12-17 08:32:00,121 INFO org.apache.hadoop.hbase.regionserver.HStore:
> Region: 0beaae111b0f6e98bfde31ba35be5408 added
> hdfs://replica-1:8020/hbase/data/default/IntegrationTestRegionReplicaReplication/544affde3e027454f67c8ea46c8f69ee/f3/e6f25e6b0eca4d22af15d0626d0f8759,
> entries=32379, sequenceid=41392, filesize=27.5 M
> 2019-12-17 08:32:00,122 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> CustomLog decrMemStoreSize. Current: dataSize=135810071,
> getHeapSize=148400960, getOffHeapSize=0, getCellsCount=167243 delta:
> dataSizeDelta=155923644, heapSizeDelta=170112320, offHeapSizeDelta=0,
> cellsCountDelta=188399
> 2019-12-17 08:32:00,122 ERROR org.apache.hadoop.hbase.regionserver.HRegion:
> Asked to modify this region's
> (IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697_0001.0beaae111b0f6e98bfde31ba35be54
> 08.) memStoreSizing to a negative value which is incorrect. Current
> memStoreSizing=135810071, delta=-155923644
> java.lang.Exception
> at
> org.apache.hadoop.hbase.regionserver.HRegion.checkNegativeMemStoreDataSize(HRegion.java:1323)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.decrMemStoreSize(HRegion.java:1316)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.decrMemStoreSize(HRegion.java:1303)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.replayWALFlushCommitMarker(HRegion.java:5194)
> at
> org.apache.hadoop.hbase.regionserver.HRegion.replayWALFlushMarker(HRegion.java:5025)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.doReplayBatchOp(RSRpcServices.java:1143)
> at
> org.apache.hadoop.hbase.regionserver.RSRpcServices.replay(RSRpcServices.java:2232)
> at
> org.apache.hadoop.hbase.shaded.protobuf.generated.AdminProtos$AdminService$2.callBlockingMethod(AdminProtos.java:29754)
> at org.apache.hadoop.hbase.ipc.RpcServer.call(RpcServer.java:413)
> at org.apache.hadoop.hbase.ipc.CallRunner.run(CallRunner.java:133)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor$Handler.run(RpcExecutor.java:338)
> at
> org.apache.hadoop.hbase.ipc.RpcExecutor$Handler.run(RpcExecutor.java:318)
> {code}
> I added some custom logging to the snapshot logic to be able to see snapshot
> sizes:
> {code:java}
> 2019-12-17 08:31:56,900 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Replaying flush marker action: START_FLUSH
> table_name: "IntegrationTestRegionReplicaReplication" encoded_region_name:
> "544affde3e027454f67c8ea46c8f69ee" flush_sequence_number: 41392 store_flushes
> { family_name: "f1" store_home_dir: "f1" } store_flushes { family_name: "f2"
> store_home_dir: "f2" } store_flushes { family_name: "f3" store_home_dir: "f3"
> } region_name:
> "IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697.544affde3e027454f67c8ea46c8f69ee."
> 2019-12-17 08:31:56,900 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> Flushing 0beaae111b0f6e98bfde31ba35be5408 3/3 column families,
> dataSize=126.49 MB heapSize=138.24 MB
> 2019-12-17 08:31:56,900 WARN
> org.apache.hadoop.hbase.regionserver.DefaultMemStore: Snapshot called again
> without clearing previous. Doing nothing. Another ongoing flush or did we
> fail last attempt?
> 2019-12-17 08:31:56,900 DEBUG
> org.apache.hadoop.hbase.regionserver.DefaultMemStore: CustomLog snapshot for
> region: {ENCODED => 0beaae111b0f6e98bfde31ba35be5408, NAME =>
> 'IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697_0001.0beaae111b0f6e98bfde31ba35be5408.',
> STARTKEY => 'bbbbbbbb', ENDKEY => 'cccccccc', REPLICA_ID => 1} memstore:
> dataSize=41660529, getHeapSize=45422304, getOffHeapSize=0, getCellsCount=49951
> 2019-12-17 08:31:56,901 DEBUG
> org.apache.hadoop.hbase.regionserver.DefaultMemStore: CustomLog snapshot for
> region: {ENCODED => 0beaae111b0f6e98bfde31ba35be5408, NAME =>
> 'IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697_0001.0beaae111b0f6e98bfde31ba35be5408.',
> STARTKEY => 'bbbbbbbb', ENDKEY => 'cccccccc', REPLICA_ID => 1} memstore:
> dataSize=72246315, getHeapSize=78890240, getOffHeapSize=0, getCellsCount=88222
> 2019-12-17 08:31:56,901 WARN
> org.apache.hadoop.hbase.regionserver.DefaultMemStore: Snapshot called again
> without clearing previous. Doing nothing. Another ongoing flush or did we
> fail last attempt?
> 2019-12-17 08:31:56,901 DEBUG
> org.apache.hadoop.hbase.regionserver.DefaultMemStore: CustomLog snapshot for
> region: {ENCODED => 0beaae111b0f6e98bfde31ba35be5408, NAME =>
> 'IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697_0001.0beaae111b0f6e98bfde31ba35be5408.',
> STARTKEY => 'bbbbbbbb', ENDKEY => 'cccccccc', REPLICA_ID => 1} memstore:
> dataSize=42016800, getHeapSize=45799776, getOffHeapSize=0, getCellsCount=50226
> 2019-12-17 08:31:56,901 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Prepared flush with seqId:41392
> {code}
> This shows that snapshots combined size is actually bigger than the region's
> memStoreSizing. So when do we decrease memStoreSizing without actually
> flushing?
> A bit earlier in the log I found this:
> {code:java}
> 2019-12-17 08:31:43,581 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Replaying flush marker action: START_FLUSH
> table_name: "IntegrationTestRegionReplicaReplication" encoded_region_name:
> "544affde3e027454f67c8ea46c8f69ee" flush_sequence_number: 40445 store_flushes
> { family_name: "f2" store_home_dir: "f2" } region_name:
> "IntegrationTestRegionReplicaReplication,bbbbbb
> bb,1576599911697.544affde3e027454f67c8ea46c8f69ee."
> 2019-12-17 08:31:43,582 WARN org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Received a flush prepare marker with a
> larger seqId: 40445 before clearing the previous one with seqId: 20747.
> Ignoring
> 2019-12-17 08:31:43,582 TRACE org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Store files for region:
> 2019-12-17 08:31:43,582 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> writing data to region
> IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697_0001.0beaae111b0f6e98bfde31ba35be5408.
> with WAL disabled. Data may be lost in the event of a crash.
> 2019-12-17 08:31:43,586 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Replaying flush marker action:
> COMMIT_FLUSH table_name: "IntegrationTestRegionReplicaReplication"
> encoded_region_name: "544affde3e027454f67c8ea46c8f69ee"
> flush_sequence_number: 40445 store_flushes { family_name: "f2"
> store_home_dir: "f2" flush_output: "3f6a5302b36a4a65a6caa291a03f108d" }
> region_name:
> "IntegrationTestRegionReplicaReplication,bbbbbbbb,1576599911697.544affde3e027454f67c8ea46c8f69ee."
> 2019-12-17 08:31:43,586 WARN org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Received a flush commit marker with larger
> seqId: 40445 than what we have prepared with seqId:
> 20747. Picking up new file and dropping prepared memstore snapshot
> 2019-12-17 08:31:43,587 WARN org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Unexpected: flush commit marker received
> from store f2 but no associated flush context. Ignoring
> 2019-12-17 08:31:43,587 DEBUG org.apache.hadoop.hbase.regionserver.HRegion:
> CustomLog decrMemStoreSize. Current: dataSize=184492444,
> getHeapSize=201769960, getOffHeapSize=0, getCellsCount=229450 delta:
> dataSizeDelta=83677329, heapSizeDelta=91222080, offHeapSizeDelta=0,
> cellsCountDelta=100177
> 2019-12-17 08:31:43,587 INFO org.apache.hadoop.hbase.regionserver.HRegion:
> 0beaae111b0f6e98bfde31ba35be5408 : Not dropping memstore contents since
> replayed flush seqId: 40445 is smaller than current seqId:40481
> {code}
> Based on this the issues seems to originate from HRegion.replayFlushInStores.
> The StoreFlushContext is missing, we show a warning and continue the
> execution with the next StoreFlushDescriptor without actually flushing the
> snapshot in question. However replayWALFlushCommitMarker is unaware of the
> warn and continues assuming the flush was successful and decreasing the
> memStoreSizing (and doing cleanup).
>
> We should consider decreasing the memStoreSizing on a per store level instead
> of on the region level and do the negativity check before we do it,
> potentially preventing a flush if needed, to make sure we keep the
> memStoreSizing positive.
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