# $OpenLDAP$
-# Copyright 1999-2008 The OpenLDAP Foundation, All Rights Reserved.
+# Copyright 1999-2012 The OpenLDAP Foundation, All Rights Reserved.
# COPYING RESTRICTIONS APPLY, see COPYRIGHT.
H1: Tuning
H3: What log level to use
-The default of {{loglevel 256}} is really the best bet. There's a corollary to
+The default of {{loglevel stats}} (256) is really the best bet. There's a corollary to
this when problems *do* arise, don't try to trace them using syslog.
Use the debug flag instead, and capture slapd's stderr output. syslog is too
slow for debug tracing, and it's inherently lossy - it will throw away messages when it
messages, you should add the index. If you see one every month or so, it may
be acceptable to ignore it.
-The default syslog level is 256 which logs the basic parameters of each
+The default syslog level is stats (256) which logs the basic parameters of each
request; it usually produces 1-3 lines of output. On Solaris and systems that
only provide synchronous syslog, you may want to turn it off completely, but
usually you want to leave it enabled so that you'll be able to see index
check this number for both dn2id and id2entry.
Also note that {{id2entry}} always uses 16KB per "page", while {{dn2id}} uses whatever
-the underlying filesystem uses, typically 4 or 8KB. To avoid thrashing the,
+the underlying filesystem uses, typically 4 or 8KB. To avoid thrashing,
your cache must be at least as large as the number of internal pages in both
-the {{dn2id}} and {{id2entry}} databases, plus some extra space to accommodate the actual
-leaf data pages.
+the {{dn2id}} and {{id2entry}} databases, plus some extra space to accommodate
+the actual leaf data pages.
For example, in my OpenLDAP 2.4 test database, I have an input LDIF file that's
about 360MB. With the back-hdb backend this creates a {{dn2id.bdb}} that's 68MB,
than the barest minimum. The default cache size, when nothing is configured,
is only 256KB.
-This 2.5MB number also doesn't take indexing into account. Each indexed attribute
-uses another database file of its own, using a Hash structure.
+This 2.5MB number also doesn't take indexing into account. Each indexed
+attribute results in another database file. Earlier versions of OpenLDAP
+kept these index databases in Hash format, but from OpenLDAP 2.2 onward
+the index databases are in B-tree format so the same procedure can
+be used to calculate the necessary amount of cache for each index database.
-Unlike the B-trees, where you only need to touch one data page to find an entry
-of interest, doing an index lookup generally touches multiple keys, and the
-point of a hash structure is that the keys are evenly distributed across the
-data space. That means there's no convenient compact subset of the database that
-you can keep in the cache to insure quick operation, you can pretty much expect
-references to be scattered across the whole thing. My strategy here would be to
-provide enough cache for at least 50% of all of the hash data.
+For example, if your only index is for the objectClass attribute and db_stat
+reveals that {{objectClass.bdb}} has 339 internal pages and uses 4096 byte
+pages, the additional cache needed for just this attribute index is
-> (Number of hash buckets + number of overflow pages + number of duplicate pages) * page size / 2.
-
-The objectClass index for my example database is 5.9MB and uses 3 hash buckets
-and 656 duplicate pages. So:
-
-> ( 3 + 656 ) * 4KB / 2 =~ 1.3MB.
+> (339+1) * 4KB =~ 1.3MB.
With only this index enabled, I'd figure at least a 4MB cache for this backend.
(Of course you're using a single cache shared among all of the database files,
projects / openldap / blobdiff