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HBase >> mail # dev >> Puzzling behaviour with HBase checksums


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Varun Sharma 2013-07-05, 21:55
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Re: Puzzling behaviour with HBase checksums
What value did you set for dfs.client.read.shortcircuit.skip.checksum ?

Cheers

On Fri, Jul 5, 2013 at 2:55 PM, Varun Sharma <[EMAIL PROTECTED]> wrote:

> Hi,
>
> We are running hbase with hbase.regionserver.checksum.verify set to true.
> But we are seeing an equal # of seeks for .meta files on HDFS and data
> blocks. This is rather puzzling and I dont know if its broken. The hbase
> jar is compiled against 2.0.3-alpha and this behaviour occurs for both
> 0.94.3 and 0.94.7. Shortcircuit local reads is enabled is working well
> since only the region server is accessing the disk.
>
> We run an strace limited to lseek calls and get the following:
>
> 28162 lseek(*668*, 0, SEEK_SET)           = 0
> 28162 lseek(*635*, 57479463, SEEK_SET)    = 57479463
> 28162 lseek(*2255*, 0, SEEK_SET)          = 0
> 28162 lseek(*1938*, 29285843, SEEK_SET)   = 29285843
>
> Then we use lsof to find the underlying files and match them against the
> corresponding file decriptors...
>
> java    27947 hbase * 668u *  REG             202,32   1048583 36176608
>
> /data/xvdc/hadoop/dfs/data/current/BP-1854623640-10.158.62.78-1363075060974/current/finalized/subdir54/
> *blk_5081211948968918615_597521.meta*
> *
> *
> java    27947 hbase  *635u*      REG             202,32 134217728 36176607
>
> /data/xvdc/hadoop/dfs/data/current/BP-1854623640-10.158.62.78-1363075060974/current/finalized/subdir54/
> *blk_5081211948968918615*
> *
> *
> java    27947 hbase *2255u*   REG             202,16    802375 32768850
>
> /mnt/hadoop/dfs/data/current/BP-1854623640-10.158.62.78-1363075060974/current/finalized/subdir40/
> *blk_2670783290218647110_614641.meta*
> *
> *
> java    27947 hbase *1938u*   REG             202,16 102702747 32768849
>
> /mnt/hadoop/dfs/data/current/BP-1854623640-10.158.62.78-1363075060974/current/finalized/subdir40/
> *blk_2670783290218647110*
>
> The pattern in strace is pretty clear - first the .meta is read and then
> the block is accessed. I am wondering if there are other places apart from
> the checksum where the .meta file for the HDFS block is being accessed or
> if the checksum stuff is simply broken ? It seems we are accessing 7 byte
> values in these .meta files from more strace output. Is there a way I can
> find out if the checksums were actually written out to HFiles in the first
> place ?
>
> Thanks
> Varun
>
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Varun Sharma 2013-07-06, 00:21
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Stack 2013-07-06, 22:55
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Varun Sharma 2013-07-07, 16:38
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Varun Sharma 2013-07-06, 01:52
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Varun Sharma 2013-07-06, 00:11