From b5896ba9f6047e7031e2bdee0622d543e11a6734 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:46:30 +0200 Subject: Adding upstream version 3.4.23. Signed-off-by: Daniel Baumann --- proto/LMDB_README.html | 417 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 417 insertions(+) create mode 100644 proto/LMDB_README.html (limited to 'proto/LMDB_README.html') diff --git a/proto/LMDB_README.html b/proto/LMDB_README.html new file mode 100644 index 0000000..f380c56 --- /dev/null +++ b/proto/LMDB_README.html @@ -0,0 +1,417 @@ + + + + + + +Postfix OpenLDAP LMDB Howto + + + + + + + +

Postfix OpenLDAP LMDB Howto

+ +

Introduction

+ +

Postfix uses databases of various kinds to store and look up +information. Postfix databases are specified as "type:name". OpenLDAP +LMDB (called "LMDB" from here on) implements the Postfix database +type "lmdb". The name of a Postfix LMDB database is the name of +the database file without the ".lmdb" suffix.

+ +

This document describes:

+ +

Building Postfix with LMDB support. +
+ +
Configuring LMDB settings.
+ +
Using LMDB maps with non-Postfix programs.
+ +
Required minimum LMDB patchlevel.
+ +
Credits.
+ +

+ +

Building Postfix with LMDB support

+ +

Postfix normally does not enable LMDB support. To +build Postfix with LMDB support, use something like:

+ +

+% make makefiles CCARGS="-DHAS_LMDB -I/usr/local/include" \
+    AUXLIBS_LMDB="-L/usr/local/lib -llmdb"
+% make
+

+ +

Postfix versions before 3.0 use AUXLIBS instead of AUXLIBS_LMDB. +With Postfix 3.0 and later, the old AUXLIBS variable still supports +building a statically-loaded LMDB database client, but only the new +AUXLIBS_LMDB variable supports building a dynamically-loaded or +statically-loaded LMDB database client.

+ +

+ +
Failure to use the AUXLIBS_LMDB variable will defeat the purpose +of dynamic database client loading. Every Postfix executable file +will have LMDB database library dependencies. And that was exactly +what dynamic database client loading was meant to avoid.
+ +

+ + +

Solaris may need this:

+ +

+% make makefiles CCARGS="-DHAS_LMDB -I/usr/local/include" \
+    AUXLIBS_LMDB="-R/usr/local/lib -L/usr/local/lib -llmdb"
+% make
+

+ +

The exact pathnames depend on how LMDB was installed.

+ +

When building Postfix fails with:

+ +

+undefined reference to `pthread_mutexattr_destroy'
+undefined reference to `pthread_mutexattr_init'
+undefined reference to `pthread_mutex_lock'
+

+ +

Add the "-lpthread" library to the "make makefiles" command.

+ +

+% make makefiles .... AUXLIBS_LMDB="... -lpthread"
+

+ +

Configuring LMDB settings

+ +

Postfix provides one configuration parameter that controls +LMDB database behavior.

+ +

lmdb_map_size (default: 16777216). This setting specifies +the initial LMDB database size limit in bytes. Each time a database +becomes "full", its size limit is doubled. The maximum size is the +largest signed integer value of "long".
+ +

+ +

Using LMDB maps with non-Postfix programs

+ +

Programs that use LMDB's built-in locking protocol will corrupt +a Postfix LMDB database or will read garbage.

+ +

Postfix does not use LMDB's built-in locking protocol, because +that would require world-writable lockfiles, and would violate +Postfix security policy. Instead, Postfix uses external locks based +on fcntl(2) to prevent writers from corrupting the database, and +to prevent readers from receiving garbage.

+ +

See lmdb_table(5) for a detailed description of the locking +protocol that all programs must use when they access a Postfix LMDB +database.

+ +

Required minimum LMDB patchlevel

+ +

Currently, Postfix requires LMDB 0.9.11 or later. The required +minimum LMDB patchlevel has evolved over time, as the result of +Postfix deployment experience:

+ +

LMDB 0.9.11 allows Postfix daemons to log an LMDB error +message, instead of falling out of the sky without any notification. +
+ +
LMDB 0.9.10 closes an information leak where LMDB was +writing up to 4-kbyte chunks of uninitialized heap memory to the +database. This would persist information that was not meant to be +persisted, or share information that was not meant to be shared. +
+ +
LMDB 0.9.9 allows Postfix to use external (fcntl()-based) +locks, instead of having to use world-writable LMDB lock files, +violating the Postfix security model in multiple ways.
+ +
LMDB 0.9.8 allows Postfix to recover from a "database full" +error without having to close the database. This version adds support +to update the database size limit on-the-fly. This is necessary +because Postfix database sizes vary with mail server load.
+ +
LMDB 0.9.7 allows the postmap(1) and postalias(1) commands +to use a bulk-mode transaction larger than the amount of physical +memory. This is necessary because LMDB supports databases larger +than physical memory.
+ +

+ +

Credits

+ +

Howard Chu contributed the initial Postfix dict_lmdb driver. +
+ +
Wietse Venema wrote an abstraction layer (slmdb) that +behaves more like Berkeley DB, NDBM, etc. This layer automatically +retries an LMDB request when a database needs to be resized, or +after a database was resized by a different process.
+ +
Howard and Wietse went through many iterations with changes +to both LMDB and Postfix, with input from Viktor Dukhovni.
+ +

+ + + + + + + + + + + + + + + + + + -- cgit v1.2.3