On 16.03.2011 19:35, Robert Haas wrote:
3. If synchronous_standby_names is changed to '' by editing postgresql.conf and issuing pg_ctl reload, then cancel all waits in progress and wake everybody up. As I mentioned before, reloading the config file from within the waiting backend (which can't safely throw an error) seems risky, so what I did instead is made WAL writer responsible for handling this. Nobody's allowed to wait for sync rep unless a global shared memory flag is set, and the WAL writer process is responsible for setting and clearing this flag when the config file is reloaded. This has basically no performance cost; WAL writer only ever does any extra work at all with this code when it receives a SIGHUP, and even then the work is trivial except in the case where synchronous_standby_names has changed from empty to non-empty or visca versa. The advantage of putting this in WAL writer rather than, say, bgwriter is that WAL writer doesn't have nearly as many jobs to do and they don't involve nearly as much I/O, so the chances of a long delay due to the process being busy are much less.
Hmm, so setting synchronous_standby_names to '' takes effect immediately, but other changes to it don't apply to already-blocked commits. That seems a bit inconsistent. Perhaps walwriter should store the parsed list of standby-names in shared memory, not just a boolean.
+1 otherwise. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
