Martijn van Oosterhout <klep...@svana.org> writes: > On Wed, Aug 03, 2011 at 02:21:25PM -0400, Robert Haas wrote: >> It would be nice if the Linux guys would fix this problem for us, but >> I'm not sure whether they will. For those who may be curious, the >> problem is in generic_file_llseek() in fs/read-write.c. On a platform >> with 8-byte atomic reads, it seems like it ought to be very possible >> to read inode->i_size without taking a spinlock.
> Interesting. There's this thread from 2003 suggesting the use of pread > instead, it was rejected on the argument that lseek is cheap so not a > problem. > http://archives.postgresql.org/pgsql-patches/2003-02/msg00197.php That seems rather unrelated. The point here is our use of lseek to find out the current file size --- or at least, I would hope they're not trying to read the inode's file size in a SEEK_CUR call. The reason "-M prepared" helps is presumably that it eliminates most of the RelationGetNumberOfBlocks calls the planner does to check current table size. While we could certainly consider using a cheaper (possibly more stale) value there, it's a bit astonishing to think that that's the main cost in a parse/plan/execute cycle. Perhaps there are more hotspot calls than that one? 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
