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From "Kelvin Kakugawa (JIRA)" <>
Subject [jira] Commented: (CASSANDRA-1546) (Yet another) approach to counting
Date Sat, 09 Oct 2010 02:06:35 GMT


Kelvin Kakugawa commented on CASSANDRA-1546:


np, let me clarify.  The way both #1546 and #1072 work is that counter updates are only aggregated
in the MT.  You can imagine that each SST on-disk represents the aggregated updates for those
keys when they were MTs (in the past)--snapshots in time, if you will.  So, on a counter read,
the counts for a given key are aggregated across all the relevant SSTs on disk.  On a related
note, during compaction, counts across the compacted SSTs are aggregated into the resultant
SST.  So, writes are cheap.

You may want to reference my presentation on distributed counters:

> (Yet another) approach to counting
> ----------------------------------
>                 Key: CASSANDRA-1546
>                 URL:
>             Project: Cassandra
>          Issue Type: New Feature
>          Components: Core
>            Reporter: Sylvain Lebresne
>            Assignee: Sylvain Lebresne
>             Fix For: 0.7.0
>         Attachments: 0001-Remove-IClock-from-internals.patch, 0001-v2-Remove-IClock-from-internals.patch,
0001-v3-Remove-IClock-from-internals.txt, 0002-Counters.patch, 0002-v2-Counters.patch, 0002-v3-Counters.txt,
0003-Generated-thrift-files-changes.patch, 0003-v2-Thrift-changes.patch, 0003-v3-Thrift-changes.txt,
> This could be described as a mix between CASSANDRA-1072 without clocks and CASSANDRA-1421.
> More details in the comment below.

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