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Re: Overlays: freeing resources on a hijacked Operation
David Hawes wrote:
I have recently finished an overlay that I call 'addpartial' that
intercepts an add operation, determines if the entry to be added
exists, and if so, determines if anything has changed and modifies
the appropriate attributes. If the entry does not exist, the add
proceeds as expected. If the entry does exist yet is identical to
the existing entry, the add will silently return LDAP_SUCCESS. The
intent of this overlay is to do partial record replication from a
master to its slaves, while upstream replication data (from our
Registry, in this case) can be full records. Before this overlay, we
were doing deletes and adds for each entry changed in our Registry
(ugh!), so we were effectively slowing down our directories. The
overlay can do a steady 400-500 records compared per second on
entries with approximately 20-40 attributes (very rough numbers). I
know other people faced with this problem effectively diff entries at
another level--this overlay simply does that at the LDAP level. I
provide this information in the hope that others will find this
useful. I'd love to polish it up and contribute it, if so.
Sounds good. This is exactly the behavior that I want to add to the
syncrepl consumer, which currently does a full Delete/Add on modifications.
My apologies for that long-winded description. Now on to my
After the overlay has finished doing what it needs to do, it sends
LDAP_SUCCESS to the client and then returns. If I return
LDAP_SUCCESS, my server runs out of memory at around 1 million
entries (starts eating up swap and then segfaults). However, if I
return SLAP_CB_CONTINUE, the server does not run out of memory
(tested up to 20 million entries). I assume that something in the
original add Operation needs to be freed, but I am not sure what.
Could anyone point me in the right direction for this case? The
overlay works fine when I return SLAP_CB_CONTINUE, but there are some
misleading errors left in the logs (68: entry already exists) as it
tries to complete the original operation.
I appreciate any help or guidance for this. Also, I have to say I
really love the concept of overlays.
Looking at the current HEAD code, I don't see anything obvious. Since
you didn't mention what version you're working with, we have no point of
reference from which to start guiding you. Without knowing what your
code looks like, there's no way for us to tell what is being leaked, and
guessing won't be very helpful.
I suggest you run your code under a malloc debugger and let it tell you
exactly what is being leaked. valgrind on linux is really good for this
sort of thing. If you're using Solaris you can use my FunctionCheck
1.5.3 package. http://highlandsun.com/hyc/fncchk153.tgz
FunctionCheck works on Linux also, of course. Which to use depends on
the problem you're chasing; valgrind can work with your existing
binaries but since it runs your code using a CPU emulator, it is
hundreds of times slower than normal execution. FunctionCheck requires
you to recompile your code specially with gcc, but it runs on the real
CPU so it's only marginally slower than normal. When the problem you're
chasing can be reproduced quickly and easily, valgrind is probably the
easier approach. When the problem occurs rarely, and requires a lot of
operations to reproduce, it may be faster overall to use FunctionCheck.
-- Howard Chu
Chief Architect, Symas Corp. Director, Highland Sun
Symas: Premier OpenSource Development and Support