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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Updated] (CASSANDRA-2498) Improve read performance in update-intensive workload
Date Sat, 13 Aug 2011 06:04:27 GMT


Jonathan Ellis updated CASSANDRA-2498:

    Attachment: 2498-v3.txt

v3 attached.

bq. CollationController.collectSSTablesWith*Filter should move to the filter implementations,

Feels like one step forward, one step back to me, since that starts to de-encapsulate "iterables."
 Also, special-casing counters means that we use the "slice" method for name-based counter
queries.  (Renamed the methods to reflect this.)

bq. Could maintain the SSTables in DataTracker.View in sorted order according to SSTable.sortNewestDataFirst

Good idea.  Done.

bq. The comment "Caller is responsible for final removeDeleted" isn't relevant to collectSSTablesWithNameFilter

Are you sure?  It's not the _immediate_ caller anymore, but we're still going back up to CFS.getCF
via getTLC, and we still need to do a final removeDeleted there.

bq. we'll need to special case Counters here


> Improve read performance in update-intensive workload
> -----------------------------------------------------
>                 Key: CASSANDRA-2498
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Ellis
>            Assignee: Sylvain Lebresne
>            Priority: Minor
>              Labels: ponies
>             Fix For: 1.0
>         Attachments: 2498-v2.txt, 2498-v3.txt, supersede-name-filter-collations.patch
> Read performance in an update-heavy environment relies heavily on compaction to maintain
good throughput. (This is not the case for workloads where rows are only inserted once, because
the bloom filter keeps us from having to check sstables unnecessarily.)
> Very early versions of Cassandra attempted to mitigate this by checking sstables in descending
generation order (mostly equivalent to descending mtime): once all the requested columns were
found, it would not check any older sstables.
> This was incorrect, because data timestamp will not correspond to sstable timestamp,
both because compaction has the side effect of "refreshing" data to a newer sstable, and because
hintead handoff may send us data older than what we already have.
> Instead, we could create a per-sstable piece of metadata containing the most recent (client-specified)
timestamp for any column in the sstable.  We could then sort sstables by this timestamp instead,
and perform a similar optimization (if the remaining sstable client-timestamps are older than
the oldest column found in the desired result set so far, we don't need to look further).
Since under almost every workload, client timestamps of data in a given sstable will tend
to be similar, we expect this to cut the number of sstables down proportionally to how frequently
each column in the row is updated. (If each column is updated with each write, we only have
to check a single sstable.)
> This may also be useful information when deciding which SSTables to compact.
> (Note that this optimization is only appropriate for named-column queries, not slice
queries, since we don't know what non-overlapping columns may exist in older sstables.)

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