Re: commit: ldap/servers/slapd entry.c proto-slap.h slap.h zn_malloc.c

["Jong-Hyuk" <jongchoi@watson.ibm.com>]

> Looks cool. Can you please remind me what this is doing? You detect when
> physical memory is exhausted by noticing increased swap space usage? I
> suppose one might get a similar effect by just setting the memoryuse
> limit before running slapd, except that we would have to change the
> behavior of ch_malloc and its callers.

The main goal of the adaptive caching is to make slapd's performance robust
to physical memory shortage as well as to make it benefit from the low
latency of the application-level entry caching. It enables autonomic
management of the degree of entry caching which can dynamically adapt to
changing availability of memory in the system. In addition, because of the
zone-based memory allocator, the performance behavior upon swapping (incl.
ones caused by other apps or underlying system) will be improved by much.
Look at http://www.openldap.org/conf/odd-sandiego-2004/Jonghyuk.pdf  for
performance implication and early evaluation results.
The resource limit approach can be considered as a static approach whereas
the adaptive caching can be considered as a more dynamic management of entry
caching which can adapt to the changing system condition. In addition, with
the conventional malloc and resource limit approach, it does not seem
feasible to decrease the footprint of the entry cache without writing them
back to the swap device. With the zone-based memory allocator, it is
possible to yank the memory pages in the victim zone upon memory shortage.
The entry cache entries which were contained in those pages can be
reconstructed from the database when they are accessed later.
- Jong-Hyuk