Berkeley DB: DB_ENV->set_mp_mmapsize
Description: Berkeley DB: An embedded database programmatic toolkit.
Keywords: embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++

### DB_ENV->set_mp_mmapsize |

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###

    #include <db.h>

    int
    DB_ENV->set_mp_mmapsize(DB_ENV *dbenv, size_t mp_mmapsize);

    int
    DB_ENV->get_mp_mmapsize(DB_ENV *dbenv, size_t *mp_mmapsizep);

### Description: DB_ENV->set_mp_mmapsize

Files that are opened read-only in the pool (and that satisfy a few other criteria) are, by default, mapped into the process address space instead of being copied into the local cache. This can result in better-than-usual performance because available virtual memory is normally much larger than the local cache, and page faults are faster than page copying on many systems. However, it can cause resource starvation in the presence of limited virtual memory, and it can result in immense process sizes in the presence of large databases.

The DB_ENV->get_mp_mmapsize method sets the maximum file size, in bytes, for a file to be mapped into the process address space. If no value is specified, it defaults to 10MB.

The database environment's maximum mapped file size may also be configured using the environment's DB_CONFIG file. The syntax of the entry in that file is a single line with the string "set_mp_mmapsize", one or more whitespace characters, and the size in bytes. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.

The DB_ENV->set_mp_mmapsize method configures a database environment, not only operations performed using the specified DB_ENV handle.

The DB_ENV->set_mp_mmapsize method may be called at any time during the life of the application.

The DB_ENV->set_mp_mmapsize method returns a non-zero error value on failure and 0 on success.

### Parameters

mp_mmapsize
  The mp_mmapsize parameter is the maximum file size, in bytes, for a file to be mapped into the process address space.

### Errors

The DB_ENV->set_mp_mmapsize method may fail and return one of the following non-zero errors:

EINVAL
  If the method was called after DB_ENV->open was called; or if an invalid flag value or parameter was specified.

### Description: DB_ENV->get_mp_mmapsize

The DB_ENV->get_mp_mmapsize method returns the maximum file map size.

The DB_ENV->get_mp_mmapsize method may be called at any time during the life of the application.

The DB_ENV->get_mp_mmapsize method returns a non-zero error value on failure and 0 on success.

### Parameters

mp_mmapsizep
  The DB_ENV->get_mp_mmapsize method returns the maximum file map size in mp_mmapsizep.

### Class

DB_ENV, DB_MPOOLFILE

### See Also

Memory Pools and Related Methods`

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