Horton

64-bit queryId?

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2017-09-29T23:42:02Z
Lists: pgsql-hackers 
Our Query currently has space for a 32-bit queryId, but that seems
reasonably likely to result in collisions:

https://en.wikipedia.org/wiki/Birthday_problem#Probability_table

If you have as many as 50,000 queries, there's a 25% probability of
having at least one collision; that doesn't seem particularly
unrealistic.  Obviously, normalization reduces the number of distinct
queries a lot, but if queries are dynamically generated you might
still have quite a few of them.

How about widening the value to uint64?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. pg_stat_statements: Add a comment about the dangers of padding bytes.

  2. pg_stat_statements: Widen query IDs from 32 bits to 64 bits.