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Date: Fri, 17 Aug 2012 12:17:38 +1100 (NCT)
From: "Philip Jenvey (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (CASSANDRA-2897) Secondary indexes without
 read-before-write
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     [ https://issues.apache.org/jira/browse/CASSANDRA-2897?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Philip Jenvey updated CASSANDRA-2897:
-------------------------------------

    Attachment: 41ec9fc-2897.txt

Here's an alternative patch that also tackles just the non-compaction changes (it's a little stale, against 41ec9fc)

Briefly looking at Sam's version, I'll note that:

o Mine handles entire row deletions in Memtable

o but it lacks changes to CompositesSearcher/SchemaLoader/CFMetaDataTest (though I'm not familiar with these code paths, either)

o in KeysSearcher, I very likely should be using the compare method from getValueValidator to check for staleness (instead of naively just calling equals)
                
> Secondary indexes without read-before-write
> -------------------------------------------
>
>                 Key: CASSANDRA-2897
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2897
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.7.0
>            Reporter: Sylvain Lebresne
>            Priority: Minor
>              Labels: secondary_index
>             Fix For: 1.2.0
>
>         Attachments: 0001-CASSANDRA-2897-Secondary-indexes-without-read-before-w.txt, 41ec9fc-2897.txt
>
>
> Currently, secondary index updates require a read-before-write to maintain the index consistency. Keeping the index consistent at all time is not necessary however. We could let the (secondary) index get inconsistent on writes and repair those on reads. This would be easy because on reads, we make sure to request the indexed columns anyway, so we can just skip the row that are not needed and repair the index at the same time.
> This does trade work on writes for work on reads. However, read-before-write is sufficiently costly that it will likely be a win overall.
> There is (at least) two small technical difficulties here though:
> # If we repair on read, this will be racy with writes, so we'll probably have to synchronize there.
> # We probably shouldn't only rely on read to repair and we should also have a task to repair the index for things that are rarely read. It's unclear how to make that low impact though.

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