postgres 8.4.4 on openSUSE 11.3 (2.6.36rc7, x86_64). I was watching a fairly large query run and observed that the disk light went out. I checked 'top' and postgres was using 100% CPU so I strace'd the running process. This is what I saw:
lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(87, 0, SEEK_END) = 585531392 lseek(94, 270680064, SEEK_SET) = 270680064 read(94, "<elided>"..., 8192) = 8192 and I observed that pattern quite a bit. I know lseek is cheap, but a superfluous systemcall is a superfluous systemcall, and over a short period amounted to 37% (according to strace) of the time spent in the system. What's with the excess calls to lseek? The query plan was a nested loop anti-join (on purpose). -- Jon -- Sent via pgsql-performance mailing list (pgsql-performance@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
