On Tue, 04 Oct 2011 18:47:21 -0600, Alex Rousskov wrote:
On 10/04/2011 04:21 PM, Andrew Beverley wrote:
On Tue, 2011-10-04 at 18:59 +0100, Andrew Beverley wrote:
> However, I'm now having problems with multiple instances of the
session
> helper writing to the same database. I thought I had fixed this
with the
> ->sync option, but it appears not. If I open multiple instances
of
> ext_session_acl in terminal windows on the same database, then I
do not
> get consistent results between each process. If I do a "LOGIN" on
one,
> then I can still get "No session available" on the other. Any
ideas why
> this might be? Is it a bug with db-185? Debugging shows that the
key
> does not exist in the second process, despite having been written
in the
> first.
After further investigation, the problem appears to be that the
*read*
database process is being cached (I'm not sure where). So even if
the
writing process syncs its changes to the DB file, these aren't
reflected
in the process that is reading the DB file.
After a lot of Googling, the only way I can see to fix this is to
close
and re-open the database on every read. This is very messy, but does
anyone have any better suggestions?
Hi Andrew,
FWIW, the ssl_crtd daemon which stores generated SSL certificates
on
disk does [lock and] reopen the database every time it needs to read
it.
This is not efficient, but avoids conflicts and stale info.
If you do not like that simple but inefficient approach, you can use
a
better database that can handle concurrency (and leave all caching to
it) OR implement your own custom and efficient database, possibly
using shared memory.
Disclaimer: I do not remember what database the session helper is
using
so I may be overlooking simpler/better options.
An ancient version of BerkleyDB. Mostly because the *.db API became
much less simple and potentially slower in later versions.
An upgrade is well overdue, but only really worth doing if this sync
bug is fixed.
Amos
