[PATCH] lib: Fix gencache_del

[Ralph Boehme]

On Fri, Mar 04, 2016 at 01:18:47PM +0100, Volker Lendecke wrote:
> On Fri, Mar 04, 2016 at 08:15:51AM +0100, Volker Lendecke wrote:
> > On Thu, Mar 03, 2016 at 07:08:18PM +0100, Michael Adam wrote:
> > > Unfortunately, this fails make test due to a slight
> > > change in semantics of delete:
> > 
> > Attached find a patchset that survived a private autobuild for me.
> > 
> > Comments welcome!
> 
> Not a good day for me today. Working on the next version of this
> patchset.

maybe we should get rid of the double (or tripple with memcache) cache
layering and use lmdb for the gencache.

I did a quick prototype with gencache on top of your dbwrap_lmdb
patches and ran some random artificial torture based benchmarks.

tdb:

$ sudo ./bin/smbtorture3 //localhost/normal -Uralph%... LOCAL-GENCACHE
using seed 1457257817
host=localhost share=normal user=ralph myname=sernet
Running LOCAL-GENCACHE
../source3/torture/torture.c:8248: loop took 14396469 us
LOCAL-GENCACHE took 14.5311 secs

lmdb:

$ sudo ./bin/smbtorture3 //localhost/normal -Uralph%... LOCAL-GENCACHE
using seed 1457257675
host=localhost share=normal user=ralph myname=sernet
Running LOCAL-GENCACHE
Opening /opt/samba/var/cache/gencache.tdb with lmdb
../source3/torture/torture.c:8248: loop took 5890560 us
LOCAL-GENCACHE took 6.10858 secs

This is on top of master, not on top of your patchset, I'll do that
next. I'd expect times will be much closer then as it gets rid of the
memcache and the fcntl locking.

WIP branch:
<https://git.samba.org/?p=slow/samba.git;a=shortlog;h=refs/heads/dbwrap_lmdb>

Flamegraphs:
<https://www.samba.org/~slow/files/perf-gencache-tdb.svg>
<https://www.samba.org/~slow/files/perf-gencache-lmdb.svg>

-Ralph

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