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Date: Tue, 3 Oct 2017 18:06:01 +0000 (UTC)
From: "Joseph Lynch (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (CASSANDRA-13924) Continuous/Infectious Repair
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archived-at: Tue, 03 Oct 2017 18:06:35 -0000


     [ https://issues.apache.org/jira/browse/CASSANDRA-13924?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Joseph Lynch updated CASSANDRA-13924:
-------------------------------------
    Description: 
I've been working on a way to keep data consistent without scheduled/external/manual repair, because for large datasets repair is extremely expensive. The basic gist is to introduce a new kind of hint that keeps just the primary key of the mutation (indicating that PK needs repair) and is recorded on replicas instead of coordinators during write time. Then a periodic background task can issue read repairs to just the PKs that were mutated. The initial performance degradation of this approach is non trivial, but I believe that I can optimize it so that we are doing very little additional work (see below in the design doc for some proposed optimizations).

My extremely rough proof of concept (uses a local table instead of HintStorage, etc) so far is [in a branch|https://github.com/apache/cassandra/compare/cassandra-3.11...jolynch:continuous_repair] and has a rough [design document|https://github.com/jolynch/cassandra/blob/continuous_repair/doc/source/architecture/continuous_repair.rst. I'm working on getting benchmarks of the various optimizations, but I figured I should start this ticket before I got too deep into it.

I believe this approach is particularly good for high read rate clusters requiring consistent low latency, and for clusters that mutate a relatively small proportion of their data (since you never have to read the whole dataset, just what's being mutated). I view this as something that works _with_ incremental repair to reduce work required because with this technique we could potentially flush repaired + unrepaired sstables directly from the memtable. I also see this as something that would be enabled or disabled per table since it is so use case specific (e.g. some tables don't need repair at all). I think this is somewhat of a hybrid approach based on incremental repair, ticklers (read all partitions @ ALL), mutation based repair (CASSANDRA-8911), and hinted handoff. There are lots of tradeoffs, but I think it's worth talking about.

If anyone has feedback on the idea, I'd love to chat about it. [~bdeggleston], [~aweisberg] I chatted with you guys a bit about this at NGCC; if you have time I'd love to continue that conversation here.

  was:
I've been working on a way to keep data consistent without scheduled/external/manual repair, because for large datasets repair is extremely expensive. The basic gist is to introduce a new kind of hint that keeps just the primary key of the mutation (indicating that PK needs repair) and is recorded on replicas instead of coordinators during write time. Then a periodic background task can issue read repairs to just the PKs that were mutated. The initial performance degradation of this approach is non trivial, but I believe that I can optimize it so that we are doing very little additional work (see below in the design doc for some proposed optimizations).

My extremely rough proof of concept (uses a local table instead of HintStorage, etc) so far is [in a branch|https://github.com/apache/cassandra/compare/cassandra-3.11...jolynch:continuous_repair] and has a rough [design document|https://github.com/jolynch/cassandra/blob/c597c0fc6415e00fa8db180be5034214d148822d/doc/source/architecture/continuous_repair.rst]. I'm working on getting benchmarks of the various optimizations, but I figured I should start this ticket before I got too deep into it.

I believe this approach is particularly good for high read rate clusters requiring consistent low latency, and for clusters that mutate a relatively small proportion of their data (since you never have to read the whole dataset, just what's being mutated). I view this as something that works _with_ incremental repair to reduce work required because with this technique we could potentially flush repaired + unrepaired sstables directly from the memtable. I also see this as something that would be enabled or disabled per table since it is so use case specific (e.g. some tables don't need repair at all). I think this is somewhat of a hybrid approach based on incremental repair, ticklers (read all partitions @ ALL), mutation based repair (CASSANDRA-8911), and hinted handoff. There are lots of tradeoffs, but I think it's worth talking about.

If anyone has feedback on the idea, I'd love to chat about it. [~bdeggleston], [~aweisberg] I chatted with you guys a bit about this at NGCC; if you have time I'd love to continue that conversation here.


> Continuous/Infectious Repair
> ----------------------------
>
>                 Key: CASSANDRA-13924
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13924
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Repair
>            Reporter: Joseph Lynch
>            Priority: Minor
>
> I've been working on a way to keep data consistent without scheduled/external/manual repair, because for large datasets repair is extremely expensive. The basic gist is to introduce a new kind of hint that keeps just the primary key of the mutation (indicating that PK needs repair) and is recorded on replicas instead of coordinators during write time. Then a periodic background task can issue read repairs to just the PKs that were mutated. The initial performance degradation of this approach is non trivial, but I believe that I can optimize it so that we are doing very little additional work (see below in the design doc for some proposed optimizations).
> My extremely rough proof of concept (uses a local table instead of HintStorage, etc) so far is [in a branch|https://github.com/apache/cassandra/compare/cassandra-3.11...jolynch:continuous_repair] and has a rough [design document|https://github.com/jolynch/cassandra/blob/continuous_repair/doc/source/architecture/continuous_repair.rst. I'm working on getting benchmarks of the various optimizations, but I figured I should start this ticket before I got too deep into it.
> I believe this approach is particularly good for high read rate clusters requiring consistent low latency, and for clusters that mutate a relatively small proportion of their data (since you never have to read the whole dataset, just what's being mutated). I view this as something that works _with_ incremental repair to reduce work required because with this technique we could potentially flush repaired + unrepaired sstables directly from the memtable. I also see this as something that would be enabled or disabled per table since it is so use case specific (e.g. some tables don't need repair at all). I think this is somewhat of a hybrid approach based on incremental repair, ticklers (read all partitions @ ALL), mutation based repair (CASSANDRA-8911), and hinted handoff. There are lots of tradeoffs, but I think it's worth talking about.
> If anyone has feedback on the idea, I'd love to chat about it. [~bdeggleston], [~aweisberg] I chatted with you guys a bit about this at NGCC; if you have time I'd love to continue that conversation here.


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