Most likely you're running into heap fragmentation problems with the default C library malloc() function. For example, see my malloc benchmarking results http://highlandsun.com/hyc/malloc/
The newer code in OpenLDAP 2.4 will delay the onset of this problem, but the only sure way to eliminate it is to either tune the malloc library (see the mallopt manpage) or replace it (using libhoard or libtcmalloc, typically).
Did you try it? The test script seems to my mind to be so simple that any problems encountered could well be quite common. Should I take it that only specially tweaked builds of openLDAP can withstand this treatment? How should one effect this malloc fix? Replacing standard lib paths and recompiling? What is the cause of this problem in the normal case?
Johan Jönemo