On January 6, 2010, Guilherme Salgado wrote: > 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 >
Yes, I think request.annotations is the right place to save this information. -- Francis J. Lacoste [email protected]
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