In short: The available timecounters on Google Compute Instances seem to be random.
The setting in the official FreeBSD image is wrong (not available on any of my test instances). FreeBSD will pick up a timecounter at random.
When either the TSC or the TSC-low counter is used, explain analyze behaves normally. The system clock will be wrong with a few seconds in each minute. ntpd won’t (and shouldn’t) fix that. Daemons panic. Time travel gets real.
When ACPI-fast is used, the system clock stays normal. However, an "explain analyze select count(1) from table" will run for 30000ms instead of 300ms.
pg_test_timing doesn’t show the problem, or I read the output wrong. In long: https://forums.freebsd.org/threads/58666/ Notes: $ pg_test_timing Testing timing overhead for 3 seconds. Per loop time including overhead: 6346.80 nsec Histogram of timing durations: < usec % of total count 1 0.00000 0 2 0.00000 0 4 0.00000 0 8 96.37600 455552 16 2.26939 10727 32 0.62727 2965 64 0.08801 416 128 0.56634 2677 256 0.04824 228 512 0.01523 72 1024 0.00508 24 2048 0.00275 13 4096 0.00085 4 8192 0.00042 2 16384 0.00000 0 32768 0.00021 1 65536 0.00000 0 131072 0.00021 1 -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
