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From "Eshcar Hillel (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-14920) Compacting Memstore
Date Thu, 31 Mar 2016 05:32:25 GMT

    [ https://issues.apache.org/jira/browse/HBASE-14920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15219382#comment-15219382

Eshcar Hillel commented on HBASE-14920:

I recently updated YCSB to support also delete operations.
The delete operations in the benchmark I ran ended up as cells of type *DeleteFamily*. I would
expect tombstones to be of type Delete. 
This could be an issue with my YCSB client, so we can ignore this for the moment. 
Anyone else had the same problem before?
What exactly is the affect of a cell of type DeleteFamily in a normal disk compaction? does
it remove all the entries in the column family?

[~anoop.hbase] The patch is in RB (there's a link to it in the Jira).

An in-memory compaction removes entries from the memory, much like a flush to disk would do.
The only reason to keep records in WAL is when data is *not yet* persistent on disk. 
If we remove data from memory (during in-memory compaction) so it will never arrive to disk
(since a more recent version already exists), no point in keeping the records in WAL, and
it can be removed from it.

To summarize this point, in the case of a compacting memstore tombstones are not removed during
in-memory compaction (this is the equivalent of minor compaction) and need to wait till they
hit the disk to be removed in a major compaction.

> Compacting Memstore
> -------------------
>                 Key: HBASE-14920
>                 URL: https://issues.apache.org/jira/browse/HBASE-14920
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Eshcar Hillel
>            Assignee: Eshcar Hillel
>         Attachments: HBASE-14920-V01.patch, HBASE-14920-V02.patch, move.to.junit4.patch
> Implementation of a new compacting memstore with non-optimized immutable segment representation

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