Repository: hbase Updated Branches: refs/heads/branch-2 6a3af2e52 -> 35296e590
HBASE-18504 Add documentation for WAL compression Signed-off-by: Michael Stack <st...@apache.org> Signed-off-by: Chia-Ping Tsai <chia7...@gmail.com> Project: http://git-wip-us.apache.org/repos/asf/hbase/repo Commit: http://git-wip-us.apache.org/repos/asf/hbase/commit/35296e59 Tree: http://git-wip-us.apache.org/repos/asf/hbase/tree/35296e59 Diff: http://git-wip-us.apache.org/repos/asf/hbase/diff/35296e59 Branch: refs/heads/branch-2 Commit: 35296e5902f324afd2cf8075a5ae5a1cf8eea9bb Parents: 6a3af2e Author: Peter Somogyi <psomo...@cloudera.com> Authored: Wed Aug 2 17:00:52 2017 +0200 Committer: Chia-Ping Tsai <chia7...@gmail.com> Committed: Tue Dec 19 23:39:13 2017 +0800 ---------------------------------------------------------------------- src/main/asciidoc/_chapters/architecture.adoc | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/hbase/blob/35296e59/src/main/asciidoc/_chapters/architecture.adoc ---------------------------------------------------------------------- diff --git a/src/main/asciidoc/_chapters/architecture.adoc b/src/main/asciidoc/_chapters/architecture.adoc index 9a3cbd9..1c9671d 100644 --- a/src/main/asciidoc/_chapters/architecture.adoc +++ b/src/main/asciidoc/_chapters/architecture.adoc @@ -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
