On 18/09/2007, Sander Steffann <s.steffann@xxxxxxxxxxx> wrote: > Hi, > > > Can I add SHM with merely by managing the entry in sysctl.conf? My > > current values: > > > > kernel.shmmax = 536870912 > > kernel.shmall = 536870912 > > > > My "shared_buffers" in postgresql.conf is "20000". From the website > > http://www.desknow.com/kb/idx/12/061/article/ I notice that shmmax > > should be sharedbuffer*8192, so I suppose my shmmax can be much lower > > than the above, but I raised it for performance. Am I wrong to do so? > > You need to configure the kernel so it allows processes to use more shared > memory. This does not mean that a process automatically uses it. For > PostgreSQL you will need to increase shared_buffers to make it use the extra > available shared memory. With your shared memory settings you can probably > increase shared_buffers to about 65000. > Thanks, the IPCS command shows me this: ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x0052e2c1 6782976 postgres 600 176668672 2 Now, I can merrily increase the shared_buffers, but the manual warns me against increasing the value too much because it is "per transaction" value. So here's the conflict for a novice like me: 1. Do not increase shared_buffer too much because it is per-transaction. 2. Do increase the SHM for performance, but it is only useful if you also increase shared_buffer. So which is it? Would it help to increase the effective_cache_size? It is currently at "512000". I have 4GB ram on the machine, but am willing to devote about 2GB to pgsql. Thanks! ---------------------------(end of broadcast)--------------------------- TIP 9: In versions below 8.0, the planner will ignore your desire to choose an index scan if your joining column's datatypes do not match
