Thomas Munro wrote: > One thing I noticed is that there are ~4 billion members (that's how > many you have when you run out of member space), but only ~128 million > multixacts, so I think the average multixact has ~32 members. > Considering the way that multixacts grow by copying and extending by > one, by the time you've created a multixact with n members you've > eaten a total of n! member space with an average size of n/2 per > multixact... So one way to hit that average would be to repeatedly > build ~64 member multixacts, or if mixed with smaller ones then you'd > need to be intermittently building even larger ones. A thundering > herd of worker processes repeatedly share-locking the same row or > something like that?
Note that the behavior of 9.5 is quite different from that of 9.3/9.4; in the older releases there is some nasty behavior involving multiple subtransactions of the same transaction grabbing a lock on the same tuple, whereby the multixact grows without bound. In 9.5 we fixed that. There's a patch in the thread for bug #8470 that fixes it for 9.3 and probably it can be applied to 9.4 too, not sure. You can see it here: https://www.postgresql.org/message-id/20150410161704.gh4...@alvh.no-ip.org Look for the "simple" formulation. I don't think I posted an updated version later, but it was never applied. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
