bdb cache deadlock case (ITS#3239)

[jongchoi@OpenLDAP.org]

Full_Name: Jong-Hyuk Choi
Version: HEAD
OS: Fedora Core 2 (Linux Kernel 2.6.5-1)
URL: ftp://ftp.openldap.org/incoming/bt040716.txt
Submission from: (NULL) (129.34.20.23)


This case was found during a syncrepl test but is apparently a bdb locking
issue.
In fact, I was going to test OPENLDAP_REL_ENG_2_2, but due to another issue in
it, I tested HEAD instead. I ran the master slapd and set off three ldapadds in
parallel each of which was to add about 132K entries. After a few minutes, I
started one syncrepl replica server. It worked without a problem for a few
minutes before the master slapd got stuck. I'll upload the stack trace. It is
quite strange to see that what is blocked is TXN_ABORT() in thread 6 bdb_add()
..... add.c:111
- Jong-Hyuk