Обсуждение: How much memory?
Is there a rule-of-thumb for determining the amount of system memory a database requres (other than "all you can afford")?
Databases basically come in 4 sizes: 1= The entire DB fits into memory. 2= The performance critical table(s) fit(s) into memory 3= The indexes of the performance critical table(s) fit into memory. 4= Neither the performance critical tables nor their indexes fit into memory. Performance decreases (exponentially), and development + maintenance cost/difficulty/pain increases (exponentially), as yougo down the list. While it is often not possible to be in class "1" above, do everything you can to be in at least class "3" and do everythingyou can to avoid class "4". At ~$75-$150 per GB as of this post, RAM is the cheapest investment you can make in a high perfomance, low hassle DBMS. IWill's and Tyan's 16 DIMM slot mainboards are worth every penny. ron -----Original Message----- From: PostgreSQL <martin@portant.com> Sent: Oct 27, 2005 3:31 PM To: pgsql-performance@postgresql.org Subject: [PERFORM] How much memory? Is there a rule-of-thumb for determining the amount of system memory a database requres (other than "all you can afford")?
On Thu, Oct 27, 2005 at 06:39:33PM -0400, Ron Peacetree wrote: > Databases basically come in 4 sizes: > > 1= The entire DB fits into memory. > 2= The performance critical table(s) fit(s) into memory > 3= The indexes of the performance critical table(s) fit into memory. > 4= Neither the performance critical tables nor their indexes fit into memory. > > Performance decreases (exponentially), and development + maintenance cost/difficulty/pain increases (exponentially), asyou go down the list. > > While it is often not possible to be in class "1" above, do everything you can to be in at least class "3" and do everythingyou can to avoid class "4". > > At ~$75-$150 per GB as of this post, RAM is the cheapest investment you can make in a high perfomance, low hassle DBMS. IWill's and Tyan's 16 DIMM slot mainboards are worth every penny. And note that your next investment after RAM should be better disk IO. More CPUs *generally* don't buy you much (if anything). My rule of thumb: the only time your database should be CPU-bound is if you've got a bad design*. *NOTE: before everyone goes off about query parallelism and big in-memory sorts and what-not, keep in mind I said "rule of thumb". :) -- Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com Pervasive Software http://pervasive.com work: 512-231-6117 vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461
Reasons not to buy from Sun or Compaq - why get Opteron 252 when a 240 will do just fine for a fraction of the cost, which of course they don't stock, white box all the way baby ;). My box from Sun or Compaq or IBM is 2x the whitebox cost because you can't buy apples to apples. We have a bitchin' DB server for $7.5k Alex On 10/27/05, Jim C. Nasby <jnasby@pervasive.com> wrote: > On Thu, Oct 27, 2005 at 06:39:33PM -0400, Ron Peacetree wrote: > > Databases basically come in 4 sizes: > > > > 1= The entire DB fits into memory. > > 2= The performance critical table(s) fit(s) into memory > > 3= The indexes of the performance critical table(s) fit into memory. > > 4= Neither the performance critical tables nor their indexes fit into memory. > > > > Performance decreases (exponentially), and development + maintenance cost/difficulty/pain increases (exponentially),as you go down the list. > > > > While it is often not possible to be in class "1" above, do everything you can to be in at least class "3" and do everythingyou can to avoid class "4". > > > > At ~$75-$150 per GB as of this post, RAM is the cheapest investment you can make in a high perfomance, low hassle DBMS. IWill's and Tyan's 16 DIMM slot mainboards are worth every penny. > > And note that your next investment after RAM should be better disk IO. > More CPUs *generally* don't buy you much (if anything). My rule of > thumb: the only time your database should be CPU-bound is if you've got > a bad design*. > > *NOTE: before everyone goes off about query parallelism and big > in-memory sorts and what-not, keep in mind I said "rule of thumb". :) > -- > Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com > Pervasive Software http://pervasive.com work: 512-231-6117 > vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461 > > ---------------------------(end of broadcast)--------------------------- > TIP 2: Don't 'kill -9' the postmaster >