On Wed, Nov 9, 2011 at 8:16 PM, Scott Marlowe <scott.marl...@gmail.com>wrote:
> On Wed, Nov 9, 2011 at 2:25 AM, Venkat Balaji <venkat.bal...@verse.in> > wrote: > > Hello Everyone, > > I could see the following in the production server (result of the "top" M > > command) - > > PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ > > COMMAND > > 25265 postgres 15 0 3329m 2.5g 1.9g S 0.0 4.0 > > 542:47.83 postgres: writer process > > The "writer process" refers to bg_writer ? and we have shared_buffers > set to > > 1920 MB (around 1.9 GB). > > So it is using 2.5G of mem of which 1.9G is shared memory (i.e. shared > buffers) so the actual amount of RAM it's using is ~600Megs. > > I see no problem. > Is this not the indication that the shared_buffers is undersized ? > > > In an other similar situation, we have "postgres writer process" using > up 7 > > - 8 GB memory constantly. > > I doubt it. Sounds more like you're misreading the output of top. > Below is the output directly taken from our production box. As per you, the writer process is taking up 1.9g from shared_buffers and the remaining (around 5.6 GB) from RAM. Mem: 65980808k total, 65620700k used, 360108k free, 210792k buffers Swap: 1052248k total, 321144k used, 731104k free, 51721468k cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 10306 postgres 15 0 15.7g 7.5g 1.9g S 1.9 12.0 1037:05 postgres: writer process Is this not a problem ? > > pg_tune is suggesting to increase the shared_buffers to 8 GB. > > Reasonable. > > > If the shared_buffer is not enough, Postgres uses OS cache ? > > Not really how things work. The OS uses all spare memory as cache. > PostgreSQL uses shared_buffers as a cache. The OS is much more > efficient about caching in dozens of gigabytes than pgsql is. What if the shared_buffers is not enough to cache the data being read from the database ? Thanks for your help ! Regards, VB
