On Sat, Dec 29, 2012 at 7:12 PM, Peter Geoghegan <pe...@2ndquadrant.com> wrote: > On 30 December 2012 02:45, Daniel Farina <dan...@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.
We can use a longer session key and duplicate the queryid (effectively padding) a couple of times to complete the XOR. I think that makes the cases of collisions introduced by this astronomically low, as an increase over the base collision rate. -- fdr -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
