s3-passdb: Keep caches coherent

Andrew Bartlett abartlet at samba.org
Sun Aug 21 17:10:51 MDT 2011

On Sun, 2011-08-21 at 16:40 +0200, Simo Sorce wrote:
>     via  d713f9e s3-passdb: Only delete 1 entry from memcache.
>        via  99bb3ee s3-passdb: Remove always the user from getpwsid
> cache.
>        via  1152aa8 s3-passdb: Keep caches coherent 

Andreas and Simo,

It seems you have also tripped across the passdb cache - I noticed it
while working on the py_passdb layer, and wondered if you or anyone on
the list knew the full background?

In particular, I wondered if anyone had any numbers on how much the
passdb cache helps us, and if there is another way we could get that
benefit?  As you have noticed, keeping the cache coherent takes quite a
bit of effort.

In particular, we don't seem to have inter-processes cache coherency,
except for the pdb_delete_user() call. 

The only call that uses the cache, as far as I can tell, is
pdb_getsampwsid(), and it is only populated on pdb_getsampwnam()

I dug into the history of this cache, which has been moved around and
re-factored many times, but never managed to find it's original
incarnation.  Does anyone remember what it was added for?


Andrew Bartlett

Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org

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