1SLAPD-MDB(5) File Formats Manual SLAPD-MDB(5)
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6 slapd-mdb - Memory-Mapped DB backend to slapd
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9 /etc/openldap/slapd.conf
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12 The mdb backend to slapd(8) uses OpenLDAP's Lightning Memory-Mapped DB
13 (LMDB) library to store data. It relies completely on the underlying
14 operating system for memory management and does no caching of its own.
15 It is the recommended primary database backend.
16 The mdb backend is similar to the hdb backend in that it uses a hierar‐
18 chical database layout which supports subtree renames. It is both more
19 space-efficient and more execution-efficient than the bdb backend,
20 while being overall much simpler to manage.
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23 These slapd.conf options apply to the mdb backend database. That is,
24 they must follow a "database mdb" line and come before any subsequent
25 "backend" or "database" lines. Other database options are described in
26 the slapd.conf(5) manual page.
27 checkpoint <kbyte> <min>
29 Specify the frequency for flushing the database disk buffers.
30 This setting is only needed if the dbnosync option is used. The
31 checkpoint will occur if either <kbyte> data has been written or
32 <min> minutes have passed since the last checkpoint. Both argu‐
33 ments default to zero, in which case they are ignored. When the
34 <min> argument is non-zero, an internal task will run every
35 <min> minutes to perform the checkpoint. Note: currently the
36 <kbyte> setting is unimplemented.
37 dbnosync
39 Specify that on-disk database contents should not be immediately
40 synchronized with in memory changes. Enabling this option may
41 improve performance at the expense of data security. In particu‐
42 lar, if the operating system crashes before changes are flushed,
43 some number of transactions may be lost. By default, a full
44 data flush/sync is performed when each transaction is committed.
45 directory <directory>
47 Specify the directory where the LMDB files containing this data‐
48 base and associated indexes live. A separate directory must be
49 specified for each database. The default is /var/openldap-data.
50 envflags {nosync,nometasync,writemap,mapasync,nordahead}
52 Specify flags for finer-grained control of the LMDB library's
53 operation.
54 nosync This is exactly the same as the dbnosync directive.
56 nometasync
58 Flush the data on a commit, but skip the sync of the meta
59 page. This mode is slightly faster than doing a full
60 sync, but can potentially lose the last committed trans‐
61 action if the operating system crashes. If both nometa‐
62 sync and nosync are set, the nosync flag takes prece‐
63 dence.
64 writemap
66 Use a writable memory map instead of just read-only. This
67 speeds up write operations but makes the database vulner‐
68 able to corruption in case any bugs in slapd cause stray
69 writes into the mmap region.
70 mapasync
72 When using a writable memory map and performing flushes
73 on each commit, use an asynchronous flush instead of a
74 synchronous flush (the default). This option has no
75 effect if writemap has not been set. It also has no
76 effect if nosync is set.
77 nordahead
79 Turn off file readahead. Usually the OS performs reada‐
80 head on every read request. This usually boosts read per‐
81 formance but can be harmful to random access read perfor‐
82 mance if the system's memory is full and the DB is larger
83 than RAM. This option is not implemented on Windows.
84 index {<attrlist>|default} [pres,eq,approx,sub,<special>]
87 Specify the indexes to maintain for the given attribute (or list
88 of attributes). Some attributes only support a subset of
89 indexes. If only an <attr> is given, the indices specified for
90 default are maintained. Note that setting a default does not
91 imply that all attributes will be indexed. Also, for best per‐
92 formance, an eq index should always be configured for the
93 objectClass attribute.
94 A number of special index parameters may be specified. The
96 index type sub can be decomposed into subinitial, subany, and
97 subfinal indices. The special type nolang may be specified to
98 disallow use of this index by language subtypes. The special
99 type nosubtypes may be specified to disallow use of this index
100 by named subtypes. Note: changing index settings in
101 slapd.conf(5) requires rebuilding indices, see slapindex(8);
102 changing index settings dynamically by LDAPModifying "cn=config"
103 automatically causes rebuilding of the indices online in a back‐
104 ground task.
105 maxreaders <integer>
107 Specify the maximum number of threads that may have concurrent
108 read access to the database. Tools such as slapcat count as a
109 single thread, in addition to threads in any active slapd pro‐
110 cesses. The default is 126.
111 maxsize <bytes>
113 Specify the maximum size of the database in bytes. A memory map
114 of this size is allocated at startup time and the database will
115 not be allowed to grow beyond this size. The default is 10485760
116 bytes. This setting may be changed upward if the configured
117 limit needs to be increased.
118 Note: It is important to set this to as large a value as possi‐
120 ble, (relative to anticipated growth of the actual data over
121 time) since growing the size later may not be practical when the
122 system is under heavy load.
123 mode <integer>
125 Specify the file protection mode that newly created database
126 files should have. The default is 0600.
127 rtxnsize <entries>
129 Specify the maximum number of entries to process in a single
130 read transaction when executing a large search. Long-lived read
131 transactions prevent old database pages from being reused in
132 write transactions, and so can cause significant growth of the
133 database file when there is heavy write traffic. This setting
134 causes the read transaction in large searches to be released and
135 reacquired after the given number of entries has been read, to
136 give writers the opportunity to reclaim old database pages. The
137 default is 10000.
138 searchstack <depth>
140 Specify the depth of the stack used for search filter evalua‐
141 tion. Search filters are evaluated on a stack to accommodate
142 nested AND / OR clauses. An individual stack is assigned to each
143 server thread. The depth of the stack determines how complex a
144 filter can be evaluated without requiring any additional memory
145 allocation. Filters that are nested deeper than the search stack
146 depth will cause a separate stack to be allocated for that par‐
147 ticular search operation. These allocations can have a major
148 negative impact on server performance, but specifying too much
149 stack will also consume a great deal of memory. Each search
150 stack uses 512K bytes per level. The default stack depth is 16,
151 thus 8MB per thread is used.
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154 The mdb backend honors access control semantics as indicated in
155 slapd.access(5).
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158 /etc/openldap/slapd.conf
159 default slapd configuration file
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162 slapd.conf(5), slapd-config(5), slapd(8), slapadd(8), slapcat(8),
163 slapindex(8), OpenLDAP LMDB documentation.
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166 OpenLDAP Software is developed and maintained by The OpenLDAP Project
167 <http://www.openldap.org/>. OpenLDAP Software is derived from the Uni‐
168 versity of Michigan LDAP 3.3 Release. Written by Howard Chu.
169OpenLDAP 2.4.47 2018/12/19 SLAPD-MDB(5)