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HBASE-18504 Add documentation for WAL compression 

Signed-off-by: Michael Stack <stack@apache.org>
Signed-off-by: Chia-Ping Tsai <chia7712@gmail.com>
This commit is contained in:
Peter Somogyi 2017-08-02 17:00:52 +02:00 committed by Chia-Ping Tsai
parent 6a3af2e52b
commit 35296e5902
1 changed files with 16 additions and 0 deletions
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src/main/asciidoc/_chapters/architecture.adoc
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@ -1184,6 +1184,22 @@ A possible downside to WAL compression is that we lose more data from the last b
mid-write. If entries in this last block were added with new dictionary entries but we failed persist the amended
dictionary because of an abrupt termination, a read of this last block may not be able to resolve last-written entries.
[[wal.compression]]
==== WAL Compression ====
The content of the WAL can be compressed using LRU Dictionary compression.
This can be used to speed up WAL replication to different datanodes.
The dictionary can store up to 2^15^ elements; eviction starts after this number is exceeded.
To enable WAL compression, set the `hbase.regionserver.wal.enablecompression` property to `true`.
The default value for this property is `false`.
By default, WAL tag compression is turned on when WAL compression is enabled.
You can turn off WAL tag compression by setting the `hbase.regionserver.wal.tags.enablecompression` property to 'false'.
A possible downside to WAL compression is that we lose more data from the last block in the WAL if it ill-terminated
mid-write. If entries in this last block were added with new dictionary entries but we failed persist the amended
dictionary because of an abrupt termination, a read of this last block may not be able to resolve last-written entries.
[[wal.disable]]
==== Disabling the WAL