[Samba] Samba 4 slow write

[Jeremy Allison]

On Fri, Apr 24, 2015 at 07:58:46AM +0800, Jones Syue wrote:
> Hello Jeremy,
> 
> Sure here is the link to patch:
> https://drive.google.com/file/d/0B7hCXnjbSiXFWDltM2lwcVdCdGs/view?usp=sharing
> 
> Based on this push:
> s3:passdb: do not use the in-memory idmap cache (it will be removed)
> https://git.samba.org/?p=samba.git;a=commit;h=c89affbd8da230cae6df25558fe621510690392c
> 
> Not quite sure why remove it from git,
> perhaps will match new features or something new.
> Loop Michael too,
> if could help review and comment that will be great help,
> thank you.

OK, this functionality got moved into idmap_cache_find_XXXX()
functions which allow smbd to look directly into the
winbindd idmap cache via the uid_to_sid(), gid_to_sid(),
sid_to_uid(), sid_to_gid() and sids_to_unixids() functions.

These functions explicitly look inside the gencache
tdb used for all generic caching (with expiry time)
inside Samba, so this should be pretty efficient.

Does this extra layer of in-memory caching really
make such a difference on top of the caching we
are already using in the gencache tdb ?

Any chance of instrumenting this without your
patch to find out why is makes such a difference ?

Michael, do you have any good ideas on why removing
the in-memory cache hurt performance so much ?

Jeremy.