Mark,

I am no expert but this looks like a file system I/O thing. I set
hw.ata.wc=1 for a SATA drive and =0 for a SCSI drive in /boot/loader.conf on
my FreeBSD systems. That seems to provide some needed tweaking.

Yudhvir
==========
On 5/18/07, Mark Harris <[EMAIL PROTECTED]> wrote:

 We have recently ported our application to the postgres database. For the
most part performance has not been an issue; however there is one situation
that is a problem and that is the initial read of rows containing BYTEA
values that have an average size of 2 kilobytes or greater. For BYTEA values
postgres requires as much 3 seconds to read the values from disk into its
buffer cache. After the initial read into buffer cache, performance is
comparable to other commercial DBMS that we have ported to. As would be
expected the commercial DBMS are also slower to display data that is not
already in the buffer cache, but the magnitude of difference for postgres
for this type of data read from disk as opposed to read from buffer cache is
much greater.



We have vacuumed the table and played around with the database
initialization parameters in the postgresql.conf. Neither helped with this
problem.



Does anyone have any tips on improving the read from disk performance of
BYTEA data that is typically 2KB or larger?



Mark




--
Yudhvir Singh Sidhu
408 375 3134 cell

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