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From "Jonathan Ellis (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-16) Memory efficient compactions
Date Fri, 11 Jun 2010 21:15:23 GMT


Jonathan Ellis commented on CASSANDRA-16:


note that besides LazilyCompactedRowTest (which checks that in-memory and on-disk compactions
produce the same result), you can change

        if (rowSize > DatabaseDescriptor.getInMemoryCompactionLimit())


        if (true)

to force the rest of the test suite to use LCR (on-disk compaction).

> Memory efficient compactions 
> -----------------------------
>                 Key: CASSANDRA-16
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>         Environment: All
>            Reporter: Sandeep Tata
>            Assignee: Jonathan Ellis
>             Fix For: 0.7
>         Attachments: 0001-introduce-AbstractCompactedRow-PrecompactedRow.txt, 0002-make-single-pass-over-columns-for-indexing.txt,
0003-r-m-object-count-abomination.-fix-BF-serialization-to-.txt, 0004-add-LazilyCompactedRow.txt,
0005-make-row-size-64-bits.txt, 0006-make-row-size-at-which-to-drop-to-incremental-compacti.txt
> The basic idea is to allow rows to get large enough that they don't have to fit in memory
entirely, but can easily fit on a disk. The compaction algorithm today de-serializes the entire
row in memory before writing out the compacted SSTable (see ColumnFamilyStore.doCompaction()
and associated methods).
> The requirement is to have a compaction method with a lower memory requirement so we
can support rows larger than available main memory. To re-use the old FB example, if we stored
a user's inbox in a row, we'd want the inbox to grow bigger than memory so long as it fit
on disk.

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