[jira] [Resolved] (HBASE-6093) Flatten timestamps during flush and compaction

["Andrew Purtell (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-6093?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrew Purtell resolved HBASE-6093.
-----------------------------------
    Resolution: Incomplete

> Flatten timestamps during flush and compaction
> ----------------------------------------------
>
>                 Key: HBASE-6093
>                 URL: https://issues.apache.org/jira/browse/HBASE-6093
>             Project: HBase
>          Issue Type: New Feature
>          Components: io, Performance, regionserver
>            Reporter: Matt Corgan
>            Priority: Minor
>
> Many applications run with maxVersions=1 and do not care about timestamps, or they will specify one timestamp per row as a normal KeyValue rather than per-cell.
> Then, DataBlockEncoders like those in HBASE-4218 and HBASE-4676 often encode timestamps as diffs from the previous or diffs from the minimum timestamp in the block.  If all timestamps in a block are the same, they will all compress to basically <= 8 bytes total per block.  This can be 10% to 25% space savings for some schemas, and that savings is realized both on disk and in block cache.
> We could add a ColumnFamily setting flattenTimestamps=[true/false].  If true, then all timestamps are modified during a flush/compaction to the currentTimeMillis() at the start of the flush/compaction.  If all timestamps are made identical in a file, then the encoder will be able to eliminate them.
> The simplest use case is probably that where all inserts are type=Put, there are no overwrites, and there are no deletes.  As use cases get more complex, then so does the implementation.  
> For example, what happens when there is a Put and a Delete of the same cell in the same memstore?  Maybe for a flush at t=flushStartTime, the Put gets timestamp=t, and the Delete gets timestamp=t+1.  Or maybe HBASE-4241 could take care of this problem.



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