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https://issues.apache.org/jira/browse/HBASE-23205?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on HBASE-23205 started by Jeongdae Kim.
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> Correctly update the position of WALs currently being replicated.
> -----------------------------------------------------------------
>
> Key: HBASE-23205
> URL: https://issues.apache.org/jira/browse/HBASE-23205
> Project: HBase
> Issue Type: Bug
> Affects Versions: 1.5.0, 1.4.10, 1.4.11
> Reporter: Jeongdae Kim
> Assignee: Jeongdae Kim
> Priority: Major
>
> We observed a lot of old WALs were not removed from archives and their
> corresponding replication queues, while testing with 1.4.10.
> stacked old WALs are empty or have no entries to be replicated (not in
> replication table_cfs)
>
> As described in HBASE-22784, if no entries to be replicated are appended to
> WALs, log position will never be updated. As a consequence, all WALs won’t be
> removed. this issue happened since HBASE-15995.
>
> I think old WALs would not be stacked with HBASE-22784. but, it still have
> something to be fixed as below
> * log position could be updated wrongly, when log rolled, because
> lastWalPath of batches might not point to WAL currently being read.
> ** For example, after last entries to be added in batch was read from P1
> position in the WAL W1
> and then WAL rolled, and reader read until it reaches the end of old wals
> and continue reading entries from new WAL W2, and then it reached batch size.
> current read position for W2 is P2. In this case, the batch being passed to a
> shipper have walPath W1 and P2, so shipper will try to update position P2 for
> W1. it may result in data inconsistency in recovery case or update failure to
> zookeeper (znode could not exist by previous log position updates, i guess
> this case is the same case asHBASE-23169?)
> * log position could be not updated or updated to wrong position by
> pendingShipment flag introduced from HBASE-22784
> ** In shipper thread, it would not beguaranteed to update log position
> always by setting pendingShipment to false.
> If reader set the flag to true, right after shipper set it to false during
> {color:#24292e}updateLogPosition(), shipper won’t update log position.{color}
> On the other hand, while reader read filtered entries, If shipper set to
> false reader will update log position to current read position. it may lose
> data in recovery case.
> * a lot of log position updates could be happened, when most of WAL entries
> are filtered by TableCfWALEntryFilter.
> ** I think it would be better to reduce the number of log updates in that
> case, because
> ### zookeeper writes are more expensive operations than reads.(since writes
> involve synchronizing the state of all servers),
> ### even if read position was not updated, it would be harmless because all
> entries will be filtered out again in recovery process.
> I think it's enough to update log position only when wal rolled in that
> case. (to cleanup old wals)
>
> In addition, During this work, i found a minor bug which is updating
> replication buffer size wrongly by decreasing total buffer size with the size
> of bulk loaded files.
> I’d like to fix it, if it’s ok.
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