On Wed, 2010-01-06 at 20:26 +0700, Stuart Bishop wrote: > > On Wed, Jan 6, 2010 at 8:20 PM, Guilherme Salgado <[email protected]> > wrote: > > >> > After realizing that I came up with another approach, which relies only > >> > on the presence/absence of the read-only.txt file to figure out the mode > >> > we're on. On this approach, config.database.main_master/slave are gone > >> > and we use dbconfig.main_master/slave instead, which are properties in > >> > DatabaseConfig that return the appropriate value according to the mode > >> > we're on. > >> > >> Does this mean we're checking for the presence of this text file before > >> every database operation? That sounds quite IO intensive. > > > > ISTM that the presence of the file would be checked only a couple times > > (once for each of the properties in DatabaseConfig that look for that > > file) for each handler thread, as a consequence of storm creating the DB > > connections when they're first used. > > > > If that's correct, then we'll have to find a way to reset the stores in > > all threads when we switch modes -- something I didn't realize before. > > You can look for this file at the start of the request when installing > the database policy and change the database settings for just the > current thread. That is just one stat() per request rather than per > database operation. We certainly wouldn't want the appserver to be > changing from normal to read-only mode half way through handling a > request. >
I guess that'd work, but since we have other places[1] which check
whether or not we're in read only mode on every request, I think we
should cache that information somewhere so that we don't issue more than
one stat() call (on read-only.txt) for each request. Since we'll be
checking that file at the beginning of every request, we could cache it
in request.annotations, maybe?
[1] LaunchpadDatabase.connection_factory
LaunchpadSecurityPolicy.checkPermission()
LaunchpadDatabasePolicyFactory and WebServiceDatabasePolicyFactory
--
Guilherme Salgado <[email protected]>
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