|Subject||Re: [firebird-support] Forced write, page size and buffer size|
I agree with you. The performance degradation was very high on an ext4 file system ( which has barrier enabled by default ). On the other hand, I found no noticiable performance degradation on an ext3 file system ( which has barrier disabled by default ).
Having barrier disabled on a server with an ext3 file system, does FW=ON improve reliability or is it useless ?
Usually, if you turn FW = ON on Linux, and your filesystem has barrier
enabled, it will affect performance of batch updates really badly.
You would either accept the performance degradation, or disable one of
them (FW or barrier).
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ACacacfs> For reliability reasons, I decided to turn on forced writes on a
ACacacfs> database running on Linux.
ACacacfs> After that I noticed that some massive updates ( 100K records ) took
ACacacfs> nearly 5 minutes, whereas with async writes it used to take 10 seconds.
ACacacfs> One solution is, of course, disabling sync writes when doing massive
ACacacfs> updates. Unfortunately not always massive updates are under database
ACacacfs> admin control ( some end users actions can lead to massive updates,
ACacacfs> indirectly, by means of triggers ).
ACacacfs> Another aproach I tested was augmenting page size from its default
ACacacfs> value ( 4 KB ) to its maximum allowed value ( 16 KB ). The speed was
ACacacfs> notably enhaced ( 1 minute for the update + 10 seconds for the commit,
ACacacfs> but sometimes 2 seconds for the update and 40 seconds for the commit).
ACacacfs> It should be pointed out that 4 KB was fine, taking into account
ACacacfs> record size ( max. 300 bytes ) and index max depth ( always < 3 ).
ACacacfs> Going one step further, I augmented cached pages from its default (
ACacacfs> 2048 ) to 8192. Some small performance improvement was observed, but not
ACacacfs> very significative. It shoud be noted also that, with a 16 KB page size,
ACacacfs> the database has 5700 pages on disk, so there are enough cache pages to
ACacacfs> hold the entire database.
ACacacfs> Given this scenario my questions are the following:
ACacacfs> 1) Does it makes sense to activate forced writes on Linux ?
ACacacfs> 2) Is increasing the page size the right approach to improve performance
ACacacfs> ? Which are the drawbacks of setting page size to 16K ?
ACacacfs> 3) The same question stands for cache pages: is it useful ( or has
ACacacfs> disadvantages ) to have so many cache pages as there are on disk pages (
ACacacfs> provided there is enough RAM size ) ?
ACacacfs> Thanks in advance for any clue.
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