Heikki Linnakangas wrote: >> We selected a 30MB bytea with psql connected with >> "-h localhost" and found that it makes a huge >> difference whether we have SSL encryption on or off. >> >> Without SSL the SELECT finished in about a second, >> with SSL it took over 23 seconds (measured with >> \timing in psql). >> During that time, the CPU is 100% busy. >> All data are cached in memory. >> >> Is this difference as expected? Thanks for looking at that. > I tried to reproduce that, but only saw about 4x difference in the > timing, not 23x. I tried more tests on an idle server, and the factor I observe here is 3 or 4 as you say. The original measurements were taken on a server under load. > oprofile suggests that all that overhead is coming from compression. > Apparently SSL does compression automatically. Oprofile report of the > above test case with SSL enabled: > > samples % image name symbol name > 28177 74.4753 libz.so.1.2.3.4 /usr/lib/libz.so.1.2.3.4 > 1814 4.7946 postgres byteain > 1459 3.8563 libc-2.13.so __memcpy_ssse3_back > 1437 3.7982 libcrypto.so.0.9.8 /usr/lib/libcrypto.so.0.9.8 > 896 2.3682 postgres hex_encode > 304 0.8035 vmlinux-3.0.0-1-amd64 clear_page_c > 271 0.7163 libc-2.13.so __strlen_sse42 > 222 0.5868 libssl.so.0.9.8 /usr/lib/libssl.so.0.9.8 > > And without: > > samples % image name symbol name > 1601 27.4144 postgres byteain > 865 14.8116 postgres hex_encode > 835 14.2979 libc-2.13.so __memcpy_ssse3_back > 290 4.9658 vmlinux-3.0.0-1-amd64 clear_page_c > 280 4.7945 libc-2.13.so __strlen_sse42 > 184 3.1507 vmlinux-3.0.0-1-amd64 page_fault > 174 2.9795 vmlinux-3.0.0-1-amd64 put_mems_allowed > > > Maybe your data is very expensive to compress for some reason? Funny, I cannot see any calls to libz. On my system (RHEL 3, PostgreSQL 8.4.8, openssl 0.9.7a) the oprofile reports of the server process look like this: With SSL: samples % symbol name image name 5326 77.6611 (no symbol) /lib/libcrypto.so.0.9.7a 755 11.009 byteaout /magwien/postgres-8.4.8/bin/postgres 378 5.51181 __GI_memcpy /lib/tls/libc-2.3.2.so 220 3.20793 printtup /magwien/postgres-8.4.8/bin/postgres Without SSL: samples % symbol name image name 765 55.8394 byteaout /magwien/postgres-8.4.8/bin/postgres 293 21.3869 __GI_memcpy /lib/tls/libc-2.3.2.so 220 16.0584 printtup /magwien/postgres-8.4.8/bin/postgres Could that still be compression? The test I am running is: $ psql "host=localhost sslmode=... dbname=test" test=> \o /dev/null test=> select val from images where id=2; test=> \q Yours, Laurenz Albe -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
