Cedric,
> ase is a table containing 29 GB of bytea in a database of 52 GB. Every row
> on the 29GB table is grab only few times. And it will just renew OS cache
> memory every time (the server have only 8GB of ram).
> So when I remove this table (not the index) from the OS cache memory, I keep
> more interesting blocks in the OS cache memory.
effective_cache_size doesn't control what gets cached, it just tells the
planner about it.
Now, if we had an OS which could be convinced to handle caching
differently for different physical devices, then I could see wanting
this setting to be per-tablespace. For example, it would make a lot of
sense not to FS-cache any data which is on a ramdisk or superfast SSD
array. The same with archive data which you expected to be slow and
infrequently accessed on a NAS device. If your OS can do that, while
caching data from other sources, then it would make sense.
However, I don't know any current OS which allows for this. Does anyone
else?
--Josh Berkus