On 13/01/2011 14:30, Christian Walter wrote:
>
> Dear Members,
>
> We are currently using PostgreSQL 7.3 on an Embedded System (Based on
> http://www.msc-ge.com/de/produkte/com/qseven/q7-us15w.html) running
> Windows XP Embedded / SP3. The onbard flash shows the following
> performance figures:
>
> - Average read = 15,6Mb/s
> - 4Kbyte reads = 3,5Mb/s
> - 1Kbyte read = 1Mb/s
This is very slow. Have you considered something more light-weight like
SQLite?
> We are sometimes facing problems that the system seems to hang due to
> database activity and now we are looking to improve the situation. If
> the database application is running and we run the benchmark again
> figures drop down to zero so we assume that the database (and
> application) is responsible for the high load. Since the embedded flash
> is quite hard to change we are looking for solution on improving this.
> For me it seems that blocksize seems a big issue and I would like to
> know if a recompile of Postgres with a larger block size would resolve
> this?
You can, see --with-blocksize and --with-wal-blocksize arguments to
./configure, but flash memory is notorious for having really large block
sizes, on the order of 256 KiB - I suspect it would be very inefficient
if the database tried to do everything in such large blocks.
> Are there any other options which should be set for flash based disks
> since latency is a lower than on harddisks.
First, you need to confirm or find where the real problem is. Windows is
hard for debugging but you may get some information from the "perfmon"
applet.