On Tue, 21 Apr 2009, da...@lang.hm wrote:
1) Disk/controller has a proper write cache. Writes and fsync will be
fast. You can insert a few thousand individual transactions per second.
in case #1 would you expect to get significant gains from batching? doesn't
it suffer from problems similar to #2 when checkpoints hit?
Typically controllers with a write cache are doing elevator sorting across
a much larger chunk of working memory (typically >=256MB instead of <32MB
on the disk itself) which means a mix of random writes will average better
performance--on top of being able to aborb a larger chunk of them before
blocking on writes. You get some useful sorting in the OS itself, but
every layer of useful additional cache helps significantly here.
Batching is always a win because even a write-cached commit is still
pretty expensive, from the server on down the chain.
I'll see about setting up a test in the next day or so. should I be able to
script this through psql? or do I need to write a C program to test this?
You can easily compare things with psql, like in the COPY BINARY vs. TEXT
example I gave earlier, that's why I was suggesting you run your own tests
here just to get a feel for things on your data set.
--
* Greg Smith gsm...@gregsmith.com http://www.gregsmith.com Baltimore, MD
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