(ITS#9002) Add option to slapcat to honor rtxnsize setting

[quanah@openldap.org]

Full_Name: Quanah Gibson-Mount
Version: 2.4.47
OS: N/A
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (47.208.144.40)


There is currently an issue with back-mdb, where if the database is quite large
(10GB+) and the environment is experiencing a heavy write load, that if you
start a backup (slapcat or mdb_copy), the database will heavily fragment and
grow significantly in size due to the read lock from the slapcat/mdb_copy
process.

To work around this, slapcat could be given an option to honor the rtxnsize
setting in slapd.conf/cn=config.  This would allow the read lock to be released
periodically and thus reduce the amount of fragmentation that occurs during the
backup process.  There is not (at this time) a solution proposed for mdb_copy.

It should be noted in the man page section for this option that the value of
such a backup is of dubious quality, since it is no longer an exact "point in
time" representation of the database but rather a bunch of different "point in
times" stitched together into a single file.