Hi Scott, Sorry for the long mail and Thank you for the quick response, My problem is that our server shuts down unexpectedly, the settings are max_connections=1024,shared_buffers = 32MB for the machine. The following is the log snippet 2007-08-15 15:44:10 LOG: could not receive data from client: No connection could be made because the target machine actively refused it. 2007-08-15 15:44:10 LOG: unexpected EOF on client connection 2007-08-15 15:44:17 LOG: received fast shutdown request 2007-08-15 15:44:17 LOG: aborting any active transactions 2007-08-15 15:44:17 FATAL: terminating connection due to administrator command 2007-08-15 15:44:17 FATAL: the database system is shutting down 2007-08-15 15:44:17 LOG: shutting down Any clues? Regards, Anoo S -----Original Message----- From: Scott Marlowe [mailto:scott.marlowe@xxxxxxxxx] Sent: 03 September 2007 09:49 To: Anoo Sivadasan Pillai Cc: pgsql-admin@xxxxxxxxxxxxxx Subject: Re: max_connections and shared_buffers > > Hi, > > 1) I saw a comment from experts-exchage regarding shared_buffers, > where max_connections were 600 > > "2000 shared buffers were for 40 connections > For 600 connections it looks more like 30000 shared buffers - to prevent > weekly slowdown. > i.e 8KB*30000 = 240MB > > 16M work_mem * 600 = 9600MB maximum when everyone is connected. " > > Can anybody explain the logic behind the calculation? those two things are not really directly related. The minimum number of shared buffers determined by the max connections is just that. A minimum. Not the recommended value, which can often be much higher, especially on a large machine with lots of RAM. the 16M work mem * 600 has to do with the fact that if you had 600 clients connected, and they all ran a query with 1 sort (a query can have > 1 sort by the way) then it would require 600*sort_mem (now work_mem) memory for the server to handle all these sorts, on top of the memory being used for other things. sort_mem (now work_mem) is NOT allocated from already allocated memory, like shared buffers, it is allocated new from free memory. Using up too much of your free memory will make your server start swapping and slow down to a crawl. > Why 30000 shared buffers is suggested for 600 connections. Not sure. We don't have the context here. For that load, on that machine, that's what they needed. > Postgresql help says "This setting must be at least 128 kilobytes and at > least 16 kilobytes times max_connections." Right. 2 blocks (8k each) for each connection is the minimum. > 2) I want to set max_connections=1024 > > Can anybody help to suggest a proper value for shared buffers for the > settings ( if no other settings are counted ) Why do you want to set max connections to 1024? I would strongly suggest using some kind of connection pooling rather than trying to run 1k connections at once. If you need to have 100 or so connections active at once, setup a connection pool (pgpool or pgbouncer or java connection pooling etc) for that many connections to the db, and use that. Connections aren't free, they require some memory and some interaction with the other backends, and they WILL slow down your db server unnecessarily. And please, if you can, shorten your sig. It's way too long. I know, some half baked lawyer somewhere in the company told you you have to do it, but for a public mailing list it seems kinda overblown. Visit our Website at http://www.rmesi.co.in This message is confidential. You should not copy it or disclose its contents to anyone. You may use and apply the information for the intended purpose only. Internet communications are not secure; therefore, RMESI does not accept legal responsibility for the contents of this message. Any views or opinions presented are those of the author only and not of RMESI. If this email has come to you in error, please delete it, along with any attachments. Please note that RMESI may intercept incoming and outgoing email communications. Freedom of Information Act 2000 This email and any attachments may contain confidential information belonging to RMESI. Where the email and any attachments do contain information of a confidential nature, including without limitation information relating to trade secrets, special terms or prices these shall be deemed for the purpose of the Freedom of Information Act 2000 as information provided in confidence by RMESI and the disclosure of which would be prejudicial to RMESI's commercial interests. This email has been scanned for viruses by Trend ScanMail. ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate
