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From "Joshua McKenzie (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-4050) Unable to remove snapshot files on Windows while original sstables are live
Date Wed, 26 Mar 2014 19:37:16 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-4050?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13948359#comment-13948359
] 

Joshua McKenzie commented on CASSANDRA-4050:
--------------------------------------------

Attaching 1st run at converting to nio.2.  Test results on both Windows and linux at blends
of 3/1, 50/1, 100/1 write/read ratios and the inverse look to be within margin of error, though
we're not getting any huge gains out of this change.  3/1 sample:
{code:title=3/1 w/r test numbers}
         4050 mmap 3/1 r/w:
                        id, ops       ,    op/s,adj op/s,   key/s,    mean,     med,     .95,
    .99,    .999,     max,   time,   stderr
             4 threadCount, 934400    ,   31029,   31030,   31029,     0.1,     0.1,     0.2,
    0.2,     0.7,    48.3,   30.1,  0.01072
             8 threadCount, 1259400   ,   41576,   41607,   41576,     0.2,     0.2,     0.2,
    0.4,     1.1,    37.9,   30.3,  0.01139
            16 threadCount, 1478350   ,   48565,   48592,   48565,     0.3,     0.3,     0.5,
    1.0,     7.0,    73.6,   30.4,  0.01197
            24 threadCount, 1523350   ,   49177,      -0,   49177,     0.5,     0.4,     0.7,
    1.5,    19.1,    71.8,   31.0,  0.01668
            36 threadCount, 1518900   ,   48679,   48718,   48679,     0.7,     0.6,     1.1,
    2.3,    22.6,    92.7,   31.2,  0.01425
            54 threadCount, 1541050   ,   48020,   48113,   48020,     1.1,     0.9,     1.8,
    4.1,    28.6,   212.6,   32.1,  0.03217
         trunk mmap 3/1 r/w:
                        id, ops       ,    op/s,adj op/s,   key/s,    mean,     med,     .95,
    .99,    .999,     max,   time,   stderr
             4 threadCount, 926400    ,   30764,   30765,   30764,     0.1,     0.1,     0.2,
    0.2,     0.7,    24.3,   30.1,  0.00997
             8 threadCount, 1283250   ,   42495,      -0,   42495,     0.2,     0.2,     0.2,
    0.3,     0.9,    44.4,   30.2,  0.01254
            16 threadCount, 1478250   ,   48509,      -0,   48509,     0.3,     0.3,     0.5,
    0.9,     4.1,    68.0,   30.5,  0.00912
            24 threadCount, 1507900   ,   48553,   48594,   48553,     0.5,     0.4,     0.8,
    1.7,    21.2,   132.1,   31.1,  0.01290
            36 threadCount, 1515150   ,   48079,      -0,   48079,     0.7,     0.6,     1.2,
    2.7,    23.3,   103.8,   31.5,  0.01531
            54 threadCount, 1517600   ,   47826,      -0,   47826,     1.1,     0.9,     1.6,
    3.2,    25.0,   194.4,   31.7,  0.01819
{code}

I mention mmap in these results as using BufferedPoolingSegmentedFiles on both trunk and on
this patch had a noticeable negative impact on throughput, more on nio.2 than on the byte[]
raw usage.  On trunk with read-heavy workloads I'm seeing anywhere from a 30-40% hit in stress
results on read performance.  1/50 r/w ratio stress w/BufferedPoolingSegmentedFiles was still
16% slower than my testing using MmappedSegmentedFiles.  I'll be attaching a sample of the
perf #'s I've been getting to CASSANDRA-6890.

I put some yammer timers inside the RAR code on both trunk and on this branch and it looks
like #'s are comparable up to about the 60th percentile or so across all major read or rebuffer
operations - then they balloon.  In the territory of a max timestamp of 100+ms on a simple
channel seek vs. .01 on mmap'ed.  GC count during stress is roughly double at a glance - I'll
look into that further on 6890 but heap stress due to more activity on the heap is to be expected.

As noted earlier - in order to fully resolve this issue, either CASSANDRA-6890 will need to
be resolved or some alternative solution for Windows if we keep mmap'ing in.

> Unable to remove snapshot files on Windows while original sstables are live
> ---------------------------------------------------------------------------
>
>                 Key: CASSANDRA-4050
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-4050
>             Project: Cassandra
>          Issue Type: Bug
>         Environment: Windows 7
>            Reporter: Jim Newsham
>            Assignee: Joshua McKenzie
>            Priority: Minor
>         Attachments: CASSANDRA-4050_v1.patch
>
>
> I'm using Cassandra 1.0.8, on Windows 7.  When I take a snapshot of the database, I find
that I am unable to delete the snapshot directory (i.e., dir named "{datadir}\{keyspacename}\snapshots\{snapshottag}")
while Cassandra is running:  "The action can't be completed because the folder or a file in
it is open in another program.  Close the folder or file and try again" [in Windows Explorer].
 If I terminate Cassandra, then I can delete the directory with no problem.
> I expect to be able to move or delete the snapshotted files while Cassandra is running,
as this should not affect the runtime operation of Cassandra.



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