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https://issues.apache.org/jira/browse/HBASE-5954?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13754646#comment-13754646
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haosdent commented on HBASE-5954:
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[~xieliang007]If mount disk with "data=writeback", the dirty data may be in
disk cache after fsync system call return. Until the data more than a ratio in
disk cache or timer is trigger, them will flush to physics storage. We could
improve the performance of hsync by disable journal and write cache. But after
disable write cache, the whole write performance is worse than before. Fsync is
a very heavy system call, I think it is unfeasible to call fsync after every
write operation. Just post my test result about fsync roughly below:
1.ext4,noatime,barrier=1,data=ordered, enable disk write cache, enable journal,
append 4k to a file
fdatasync 25ms
fsync 25ms
2.ext4,noatime,barrier=0,data=writeback, disable disk write cache, enable
journal, append 4k to a file
fdatasync 33ms
fsync 33ms
3.ext4,noatime,barrier=0,data=writeback, disable disk write cache, disable
journal, append 4k to a file
fdatasync 8ms
fsync 8ms
> Allow proper fsync support for HBase
> ------------------------------------
>
> Key: HBASE-5954
> URL: https://issues.apache.org/jira/browse/HBASE-5954
> Project: HBase
> Issue Type: Improvement
> Reporter: Lars Hofhansl
> Assignee: Lars Hofhansl
> Priority: Critical
> Fix For: 0.98.0
>
> Attachments: 5954-trunk-hdfs-trunk.txt, 5954-trunk-hdfs-trunk-v2.txt,
> 5954-trunk-hdfs-trunk-v3.txt, 5954-trunk-hdfs-trunk-v4.txt,
> 5954-trunk-hdfs-trunk-v5.txt, 5954-trunk-hdfs-trunk-v6.txt, hbase-hdfs-744.txt
>
>
> At least get recommendation into 0.96 doc and some numbers running w/ this
> hdfs feature enabled.
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