[Tilesathome] Using RAM-drive for ROMA temp tables

[Matthias Julius]

Mathieu Arnold <mat at mat.cc> writes:

> Hum, the thing is, that, hum, let me quote postgresql's doc for you :
>
> temp_buffers (integer)
>
>     Sets the maximum number of temporary buffers used by each database
> session. These are session-local buffers used only for access to temporary
> tables. The default is eight megabytes (8MB). The setting can be changed
> within individual sessions, but only up until the first use of temporary
> tables within a session; subsequent attempts to change the value will have
> no effect on that session.
>     A session will allocate temporary buffers as needed up to the limit
> given by temp_buffers. The cost of setting a large value in sessions that
> do not actually need a lot of temporary buffers is only a buffer
> descriptor, or about 64 bytes, per increment in temp_buffers. However if a
> buffer is actually used an additional 8192 bytes will be consumed for it
> (or in general, BLCKSZ bytes). 

This is interesting, but has nothing to do with RAM disks.

>
> I've set my temp_buffers to 384M, and, I don't think one request will ever
> create temp tables that large :-)

Lucky guy with plenty of memory ...

> (128M was not, on the other hand, I believe, enough to store
> everything it would need.)

Question is how often would it be exceeded.  If it is only 1% of
requests it might not be so bad.  You certainly don't want linux to
start to swap because of postgres allocating tons of memory

Matthias