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Date: Wed, 30 Sep 2015 03:43:05 +0000 (UTC)
From: "Jonathan Shook (JIRA)" <jira@apache.org>
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Subject: [jira] [Updated] (CASSANDRA-10419) Make JBOD compaction and
 flushing more robust
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     [ https://issues.apache.org/jira/browse/CASSANDRA-10419?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Jonathan Shook updated CASSANDRA-10419:
---------------------------------------
    Description: 
With JBOD and several smaller disks, like SSDs at 1.2 TB or lower, it is possible to run out of space prematurely. With a sufficient ingestion rate, disk selection logic seems to overselect on certain JBOD targets. This causes a premature C* shutdown when there is a significant amount of space left. With DTCS, for example, it should be possible to utilize over 90% of the available space with certain settings. However in the scenario I tested, only about 50% was utilized, before a filesystem full error. (see below). It is likely that this is a scheduling challenge between high rates of ingest and smaller data directories. It would be good to use an anticipatory model if possible to more carefully select compaction targets according to fill rates. As well, if the largest sstable that can be supported is constrained by the largest JBOD extent, we should make that visible to the compaction logic where possible.

The attached image shows a test with 12 1.2TB JBOD data directories. At the end, the utilizations are:
59GiB, 83GiB, 83GiB, 97GiB, 330GiB, 589GiB, 604GiB, 630GiB, 697GiB, 1.055TiB, 1.083TB, 1092TiB,  

  was:
With JBOD and several smaller disks, like SSDs at 1.2 TB or lower, it is possible to run out of space prematurely. With a sufficient ingestion rate, disk selection logic seems to overselect on certain JBOD targets. This causes a premature C* shutdown when there is a significant amount of space left. With DTCS, for example, it should be possible to utilize over 90% of the available space with certain settings. However in the scenario I tested, only about 50% was utilized, before a filesystem full error. (see below). It is likely that this is a scheduling challenge between high rates of ingest and smaller data directories. It would be good to use an anticipatory model if possible to more carefully select compaction targets according to fill rates.

The attached image shows a test with 12 1.2TB JBOD data directories. At the end, the utilizations are:
59GiB, 83GiB, 83GiB, 97GiB, 330GiB, 589GiB, 604GiB, 630GiB, 697GiB, 1.055TiB, 1.083TB, 1092TiB,  


> Make JBOD compaction and flushing more robust
> ---------------------------------------------
>
>                 Key: CASSANDRA-10419
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-10419
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Jonathan Shook
>         Attachments: timeseries-study-overview-jbods.png
>
>
> With JBOD and several smaller disks, like SSDs at 1.2 TB or lower, it is possible to run out of space prematurely. With a sufficient ingestion rate, disk selection logic seems to overselect on certain JBOD targets. This causes a premature C* shutdown when there is a significant amount of space left. With DTCS, for example, it should be possible to utilize over 90% of the available space with certain settings. However in the scenario I tested, only about 50% was utilized, before a filesystem full error. (see below). It is likely that this is a scheduling challenge between high rates of ingest and smaller data directories. It would be good to use an anticipatory model if possible to more carefully select compaction targets according to fill rates. As well, if the largest sstable that can be supported is constrained by the largest JBOD extent, we should make that visible to the compaction logic where possible.
> The attached image shows a test with 12 1.2TB JBOD data directories. At the end, the utilizations are:
> 59GiB, 83GiB, 83GiB, 97GiB, 330GiB, 589GiB, 604GiB, 630GiB, 697GiB, 1.055TiB, 1.083TB, 1092TiB,  


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