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This is the mod_db4 apache module, providing a safe framework
for running db4 applications in the Apache 1.3 environment. In
general, it is dangerous to run db4 in a multi-process system
without some facility to coordinate recovery between
participating processes. Apache natively provides no
interface for commuication between processes, so the mod_db4
module exists to provide this communication.
Specifically, mod_db4 provides the following facilities:
o New constructors for DB and DB_ENV structures, which install
replacement open/close methods.
o Transparent caching of open DB and DB_ENV structures
o Reference counting on all structures, allowing the module to
detect the initial opening of any managed database
and automatically perform recovery.
o Automatic detection of unexpected failures (segfaults, or a
module actually calling exit() and avoiding shutdown phases,
and automatic termination of all child processes with open
database resources to attempt consistency.
mod_db4 is designed to be used as an alternative interface to db4.
To have another Apache module (for example, mod_foo) use mod_db4,
do not link mod_foo against libdb-4.2. In your mod_foo makefile,
you should
#include "mod_db4_export.h"
and add your Apache include directory to your CPPFLAGS.
In mod_foo, to create a mod_db4 managed DB_ENV, use the following:
int mod_db4_db_env_create(DB_ENV **dbenvp, u_int32_t flags);
which takes identical arguments to db_env_create().
To create a mod_db4 managed DB, use
int mod_db4_db_create(DB **dbp, DB_ENV *dbenv, u_int32_t flags);
which takes identical arguments to db_create().
Otherwise the API is completely consistent with the standard Berkeley
DB API.
For installation instructions, see the INSTALL file.
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