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Date: Tue, 22 Apr 2014 12:32:19 +0000 (UTC)
From: "Jonathan Ellis (JIRA)" <jira@apache.org>
To: commits@cassandra.apache.org
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Subject: [jira] [Comment Edited] (CASSANDRA-7031) Increase default commit
 log total space + segment size
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    [ https://issues.apache.org/jira/browse/CASSANDRA-7031?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13976690#comment-13976690 ] 

Jonathan Ellis edited comment on CASSANDRA-7031 at 4/22/14 12:31 PM:
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bq. Do we mean that there may be a 128Mb gap after the most recent archive during which no PIT restore is possible? Seems like this would be a minimal problem, as the most recent CLS is still present in the CL directory

Since one point of restore is, "I don't have the CL directory anymore" this is kind of a non-solution.

bq. we could always offer the ability to create a PITR point through force recycling the current CL segment at the requested time to make sure there is a separate backup.

So now we're forcing users to add a cron job for PITR to work?  I don't like that idea either.


was (Author: jbellis):
bq. Do we mean that there may be a 128Mb gap after the most recent archive during which no PIT restore is possible? Seems like this would be a minimal problem, as the most recent CLS is still present in the CL directory

Since one point of restore is, "I don't have the CL directory anymore" this is kind of a non-solution.

> we could always offer the ability to create a PITR point through force recycling the current CL segment at the requested time to make sure there is a separate backup.

So now we're forcing users to add a cron job for PITR to work?  I don't like that idea either.

> Increase default commit log total space + segment size
> ------------------------------------------------------
>
>                 Key: CASSANDRA-7031
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7031
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Benedict
>            Priority: Trivial
>             Fix For: 2.1 beta2
>
>         Attachments: 7031.txt
>
>
> I would like to increase the default commit log total space and segment size options for 64-bit JVMs:
> The current default of 1Gb and 32Mb is quite constrained and can have some (very minor) negative performance implications, for no major benefit: 
> # 32Mb files are actually quite small, and if during the 10s interval we have completely filled multiple of them (quite easy) it would be more efficient to write fewer larger files, as we can issue fewer fsyncs and permit the OS to schedule the writes more efficiently. On my box this has a small but noticeable impact. Although I would expect on decent server hardware this would be smaller still, since we immediately drop the pages from cache on writing there isn't a great deal of advantage to keeping the files so small. The only advantage I can see is that during a drop KS/CF or other event that forces log rollover we're wasting less space until log recycling. 128-256Mb are modest increases that seem more appropriate to me.
> # 1Gb is too small for the default total log space. We can find that we force memtable flushes as a result of log utilisation instead of memtable occupancy quite often (esp. as a result of increased effective memtable space from recent improvements), especially on machines with more addressable memory. I suggest 8Gb as a minimum. The only disadvantage of having more log data is that replay on restart may be slightly slower, but since most of the events will be ignored it should be relatively benign, and I would rather take the penalty on startup instead of during running, no matter how small the running penalty.


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