Re: [HACKERS] the number of file descriptors when using POSIX semaphore
flyusa2010 fly wrote: Hi, folks, in src/template/darwin: # Select appropriate semaphore support. Darwin 6.0 (Mac OS X 10.2) and up # support System V semaphores; before that we have to use POSIX semaphores, # which are less good for our purposes because they eat a file descriptor # per backend per max_connection slot. To my understanding, the number of descriptors created by POSIX semaphores would be # of actual clients times max_connection. However, I monitor the number of open files using sysctl, and I find that kern.num_files doesn't match the result calculated by the formula that is inferred by me... So, what would the number of file descriptors be, when using POSIX semaphore? I thought the text was wrong, but this commit reinforces that text: commit 93407d3998cc8717993dbc102f854a478985bc19 Author: Tom Lane t...@sss.pgh.pa.us Date: Wed Sep 26 00:32:46 2007 + Use SYSV semaphores rather than POSIX on Darwin = 6.0 (i.e., OS X 10.2 and up), per Chris Marcellino. This avoids consuming O(N^2) file descriptors to support N backends. Tests suggest it's about a wash for small installations, but large ones would have a problem. What numbers are you seeing? -- Bruce Momjian br...@momjian.ushttp://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] the number of file descriptors when using POSIX semaphore
Bruce Momjian br...@momjian.us writes: flyusa2010 fly wrote: in src/template/darwin: # Select appropriate semaphore support. Darwin 6.0 (Mac OS X 10.2) and up # support System V semaphores; before that we have to use POSIX semaphores, # which are less good for our purposes because they eat a file descriptor # per backend per max_connection slot. So, what would the number of file descriptors be, when using POSIX semaphore? I thought the text was wrong, but this commit reinforces that text: The text is correct, or at least as correct as it's possible to get without expending three times the verbiage. If you look in InitProcGlobal you will find that the postmaster creates MaxConnections plus autovacuum_max_workers + 1 plus NUM_AUXILIARY_PROCS semaphores. In a POSIX-semaphores implementation, each of these eats a file descriptor in the postmaster, plus another file descriptor in each child process of the postmaster. The OP claims the text is wrong, but since he failed to state what he observed, it's pretty hard to comment further. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
[HACKERS] the number of file descriptors when using POSIX semaphore
Hi, folks, in src/template/darwin: # Select appropriate semaphore support. Darwin 6.0 (Mac OS X 10.2) and up # support System V semaphores; before that we have to use POSIX semaphores, # which are less good for our purposes because they eat a file descriptor # per backend per max_connection slot. To my understanding, the number of descriptors created by POSIX semaphores would be # of actual clients times max_connection. However, I monitor the number of open files using sysctl, and I find that kern.num_files doesn't match the result calculated by the formula that is inferred by me... So, what would the number of file descriptors be, when using POSIX semaphore? Thanks!
