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https://issues.apache.org/jira/browse/JAMES-3586?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benoit Tellier closed JAMES-3586.
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Resolution: Fixed
https://github.com/apache/james-project/pull/436 contributed this
> CL one option for the Cassandra blob store
> ------------------------------------------
>
> Key: JAMES-3586
> URL: https://issues.apache.org/jira/browse/JAMES-3586
> Project: James Server
> Issue Type: Improvement
> Reporter: René Cordier
> Priority: Major
> Fix For: 3.7.0
>
> Time Spent: 2h 50m
> Remaining Estimate: 0h
>
> h2. Context
> Some users are storing all message content in Cassandra and thus stores huge
> amount of data.
> We would like to reduce the performance costs to read this large amount of
> data.
> Blobs being immutable, we have a guaranty that:
> * If we read something the value is up-to date
> * If we fail at reading something we have a guaranty the content had not
> been replicated yet. A second read with a higher consistency level will read
> the data (and consistency piggy backed on consistency levels will heal the
> data)
> Cassandra being very efficient at replicating things (think hinted handoff,
> direct asynchronous replication), we can expect that data is correctly
> duplicated before reads are attempted.
> h2. Decision
> Via a configuration option, allow optimizing blob access.
> * If enabled, perform a first read at CL one and fallback if needed by
> performing a second read at the regular CL
> * If disabled, only a read at the regular CL will be attempted
> A metric should be implemented to track the CL one hit rate, allowing an
> effective review of the effectiveness of this solution.
> h2. Consequences
> In a multiDC setup with RF=3 DC=2 this implies a factor 4 in IO reduction
> across the cluster, lowering a lot the read pressure on the Cassandra
> BlobStore.
> h2. Work to be conducted
> Add a configuration option in cassandra.properties:
> {code:bash}
> # Experimental configuration option. Defaults to false.
> # Enabling it resutls in reading strictly immutable (not deleted, not
> updated) data at CL ONE. If the data is missing,
> # we can be sure that the data had not been replicated yet, a second read is
> performed with a higher consistency level.
> # This option still offer the same level of consistency (thanks to strict
> immutability) but might result in higher resource usage in case of
> mis-behaving replication.
> # Metrics can be used to mesure the efficiency of this.
> optimistic.consistency.level.enabled=false
> {code}
>
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