What could cause sudden increase in "PARSE" stage of prepared statements?

hi
i have system when we log every query that is over 150ms.

usually we get 100-500 "parse ..." elements per minute, but there are
some cases where the number exceeds 15000 per minute (it's pretty busy
system).

the interesting fact is that io is not taxed, there is no sudden network
traffic, not more than usual queries - all looks normal, but the parses
start to take much longer.

it's 8.3.11 on x64 linux.

what I should look into to solve this mystery?

Best regards,

depesz

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