On Thu, Jul 22, 2010 at 2:45 PM, A J <s5aly@xxxxxxxxx> wrote: > Cost aside, are there any technical factors to consider before increasing > RAM (assuming the system can support it) ? Is there a sweet spot beyond > which more RAM does not help Postgres or actually harms ? > If my database is only couple of hundred Gigs, can I not just have RAM that > big and have read from buffer all the time ? On some architectures, as you add memory the memory itself becomes slower. In the old days it was Intel's brain dead VX pentium architecture that could only cache the first 64Megs of ram but could handle 256M that had issues. Since windows tended to load things from the top of memory down, having > 64 Meg could make a machine noticeably slower. Nowadays it's nothing so drastic. Some hardware can only support say 800MHz memory with 2 or 4 banks of DRAM, then 667, then 500 as you fill them up. I avoid hardware like that since dbs are often memory hungry machines. Most modern machines are actually faster as you add memory because it can now address more banks at the same time, and with AMD and Intel's latest creations more banks filled is almost always a win. To the point that having the same amount of memory, but using smaller DIMMs makes the machine faster than using fewer, larger DIMMs. Generally speaking, unless your hardware is the kind that acts up with more memory, no, adding memory will almost never hurt. But once you can cache your entire db with some room to spare in memory, adding memory won't usually help. So, what CPU / Memory architecture are you running? -- To understand recursion, one must first understand recursion. -- Sent via pgsql-admin mailing list (pgsql-admin@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-admin
