Re: ext3

[William Yu <wyu@xxxxxxxxxxx>]

You may also want to test data=journal for ext3. Most of the time, this 
is slower but for databases with logging and mail servers, it can be faster.


Mage wrote:
>          Hello,
>
> Gabor Szima asked us to translate the letter below.
>
> "I read that ext3 writeback mode is recommended for PostgreSQL. I made 
> some tests.
>
>                data=ordered        data=writeback
> ----------------------------------------------------------------------
> restoredb:             2m16.790s        1m42.367s
> UPDATE <tbl1> (17krows):    9.289s            7.147s
> UPDATE <tbl1> (17krows) (2.):    10.480s            3.778s
> VACUUM ANALYZE <tbl1>:        9.364s            0.986s !
> VACUUM FULL <tbl1>:        16.071s            2.575s
> REINDEX TABLE <tbl1>:        3.815s            1.886s
> ----------------------------------------------------------------------
>
> It's seductive.
> However I made some crash-tests too. Updated 4 tables simultaneously and 
> recurring for 10 to 120s, then powered off the machine (without the 
> reset button. i just pulled out the cable).
>
> SEQ RECOVERY-WARNINGS   VACUUM
> -------------------------------
> 01: 1650                OK        (WARNING:  invalid page header in 
> block 769 of relation "18800"; zeroing out page)
> 02: 3            FATAL        (ERROR:  could not access status of 
> transaction 37814272)
> -------------------------------        (DETAIL:  could not open file 
> "/data/pgdata/pg_clog/0024": No such file or directory)
>
> I have stopped my tests at this point because this is not for production 
> use. The database was corrupted.
>
>
> With ordered mode I got this:
>
> ext3-noatime,data=ordered:
>
> SEQ RECOVERY-WARNINGS   VACUUM
> ------------------------------
> 01: 0                   OK
> 02: 0                   OK
> 03: 0                   OK
> 04: 0                   W,OK    (relation "<tbl>" page 398 is 
> uninitialized --- fixing)
> 05: 0                   OK
> 06: 0                   OK
> 07: 0                   W,OK    (relation "<tbl>" page 911 is 
> uninitialized --- fixing)
> 08: 0                   OK
> 09: 0                   OK
> 10: 0                   OK
> ------------------------------
>
> I think that writeback mode first records the data then the inode, and 
> the ordered mode does it in reverse order.  I also mean that postgres 
> log requires the inode recorded correctly, the data loss is handled by 
> the WAL.
>
> AMD XP2000, 512MB RAM, PostgreSQL 7.4.6 (i686), linux-2.4.28, gcc-3.3.5, 
> Adaptec 29160, WD Enterprise 4360 (SCSI, SCA-80)

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