Re: pg_stat_statements: calls under-estimation propagation

On 30 December 2012 02:45, Daniel Farina <daniel@heroku.com> wrote:
> As I recall, the gist of this objection had to do with a false sense
> of stability of the hash value, and the desire to enforce the ability
> to alter it.  Here's an option: xor the hash value with the
> 'statistics session id', so it's *known* to be unstable between
> sessions.  That gets you continuity in the common case and sound
> deprecation in the less-common cases (crashes, format upgrades, stat
> resetting).

Hmm. I like the idea, but a concern there would be that you'd
introduce additional scope for collisions in the third-party utility
building time-series data from snapshots. I currently put the
probability of a collision within pg_stat_statements as 1% in the
event of a pg_stat_statements.max of 10,000.

-- 
Peter Geoghegan       http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training and Services