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diff --git a/README_FILES/LMDB_README b/README_FILES/LMDB_README new file mode 100644 index 0000000..e63640f --- /dev/null +++ b/README_FILES/LMDB_README @@ -0,0 +1,123 @@ +PPoossttffiixx OOppeennLLDDAAPP LLMMDDBB HHoowwttoo + +------------------------------------------------------------------------------- + +IInnttrroodduuccttiioonn + +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. + +BBuuiillddiinngg PPoossttffiixx wwiitthh LLMMDDBB ssuuppppoorrtt + +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" + +CCoonnffiigguurriinngg LLMMDDBB sseettttiinnggss + +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". + +UUssiinngg LLMMDDBB mmaappss wwiitthh nnoonn--PPoossttffiixx pprrooggrraammss + +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. + +RReeqquuiirreedd mmiinniimmuumm LLMMDDBB ppaattcchhlleevveell + +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. + +CCrreeddiittss + + * 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. + |