> On Tue, May 3, 2011 at 6:01 PM, Raghavendra < > raghavendra.rao@xxxxxxxxxxxxxxxx> wrote: > >> >> On Tue, May 3, 2011 at 5:37 PM, Simon Riggs <simon@xxxxxxxxxxxxxxx> >> wrote: >> >>> On Tue, May 3, 2011 at 11:54 AM, raghu ram <raghuchennuru@xxxxxxxxx> >>> wrote: >>> >>> > It may be a silly question, still out of curiosity I want to know, is >>> there >>> > any possible way to flush the Postgres Shared Memory without >>> restarting >>> the >>> > cluster. >>> > In Oracle, we can flush the SGA, can we get the same feature here.. >>> > Thanks in Advance. >>> >>> >>> The CHECKPOINT command will do this for you. >>> >> >> >> > According to PostgreSQL documentation, whenever you execute "CHECKPOINT" > in > the database,it will flush the modified data files presented in the Shared > Buffers retuned to the Disk. > > http://www.postgresql.org/docs/9.0/static/sql-checkpoint.html > > Is this clears the entire shared memory cache and same time,if i execute > fresh SQL statement, Data will be retuned from disk?? No. Checkpoint means all dirty buffers are written to the datafiles, it does not mean emptying the shared buffers. Checkpoints happen regularly so this would have an unwanted impact on performance. And besides that, there's a page cache maintained by the OS (not sure if you're running Linux or Windows). So even when the block does not exist in the shared buffers, it may be in the page cache (thus not read from the drive). Dropping the page cache is quite simple (http://linux-mm.org/Drop_Caches), emptying the shared buffers is not that simple - I guess the easiest way is to restart the db. What are you trying to achieve? Why do you need this? Tomas -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
