- Berkeley DB Reference Guide:
- Memory Pool Subsystem
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The Memory Pool subsystem is the general-purpose shared memory buffer pool used by Berkeley DB. This module is useful outside of the Berkeley DB package for processes that require page-oriented, cached, shared file access.
A memory pool is a memory cache shared among any number of threads of control. The DB_INIT_MPOOL flag to the DB_ENV->open interface opens, optionally creating a memory pool. When that pool is no longer in use, it should be closed using the DB_ENV->close interface.
The memp_fopen interface returns a DB_MPOOLFILE handle on an underlying file within the memory pool. When that handle is no longer in use, it should be closed using the memp_fclose interface. The memp_fget interface is used to retrieve pages from files in the pool. All retrieved pages must be subsequently returned using the memp_fput interface. At the time pages are returned, they may be marked dirty, which causes them to be written to the underlying file before being discarded from the pool. If there is insufficient room to bring a new page in the pool, a page is selected to be discarded from the pool using a least-recently-used algorithm. Pages in files may also be explicitly marked clean or dirty using the memp_fset interface. All dirty pages in the pool may be flushed using the memp_sync interface. All dirty pages in the pool from a single underlying file may be flushed using the memp_fsync interface.
There are additional interfaces related to the memory pool:
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Copyright Sleepycat Software @ 1.1 log @Initial revision @ text @d1 1 a1 1 @ 1.1.1.1 log @Import: RPM 4.0.3 @ text @@ 1.1.1.2 log @Import: RPM 4.0.4 @ text @d1 1 a1 1 a10 1 d19 1 a19 1 for processes that require page-oriented, shared and cached file access. d22 19 a40 31 DB_ENV->open function opens and optionally creates a memory pool. When that pool is no longer in use, it should be closed using the DB_ENV->close function.
The DB_ENV->memp_fcreate function returns a DB_MPOOLFILE handle on an underlying file within the memory pool. The file may be opened using the DB_MPOOLFILE->open function. The DB_MPOOLFILE->get function is used to retrieve pages from files in the pool. All retrieved pages must be subsequently returned using the DB_MPOOLFILE->put function. At the time pages are returned, they may be marked dirty, which causes them to be written to the underlying file before being discarded from the pool. If there is insufficient room to bring a new page in the pool, a page is selected to be discarded from the pool using a least-recently-used algorithm. Pages in files may also be explicitly marked clean or dirty using the DB_MPOOLFILE->set function. All dirty pages in the pool from the file may be flushed using the DB_MPOOLFILE->sync function. When the file handle is no longer in use, it should be closed using the DB_MPOOLFILE->close function.
There are additional configuration interfaces that apply when opening a new file in the memory pool:
There are additional interfaces for the memory pool as a whole: d43 14 a56 13 maintain a consistent percentage of clean buffers in the pool using the DB_ENV->memp_trickle function.
The DB_ENV->memp_fcreate method returns a DB_MPOOLFILE handle on an d28 1 a28 1 the DB_MPOOLFILE->open method. The DB_MPOOLFILE->get method is used to retrieve d30 1 a30 1 returned using the DB_MPOOLFILE->put method. At the time pages are returned, d36 3 a38 3 DB_MPOOLFILE->set method. All dirty pages in the pool from the file may be flushed using the DB_MPOOLFILE->sync method. When the file handle is no longer in use, it should be closed using the DB_MPOOLFILE->close method. d42 1 a42 1
| Memory Pools and Related Methods | Description |
|---|---|
| DB_ENV->set_cachesize | Set the environment cache size |
| DB_ENV->set_mp_mmapsize | Set maximum mapped-in database file size |
| DB_ENV->memp_register | Register input/output functions for a file in a memory pool |
| DB_ENV->memp_stat | Return memory pool statistics |
| DB_ENV->memp_sync | Flush pages from a memory pool |
| DB_ENV->memp_trickle | Trickle flush pages from a memory pool |
| DB_ENV->memp_fcreate | Open a file in a memory pool |
| DB_MPOOLFILE->close | Close a file in a memory pool |
| DB_MPOOLFILE->get | Get page from a file in a memory pool |
| DB_MPOOLFILE->open | Open a file in a memory pool |
| DB_MPOOLFILE->put | Return a page to a memory pool |
| DB_MPOOLFILE->set | Set memory pool page status |
| DB_MPOOLFILE->sync | Flush pages from a file in a memory pool |
| DB_MPOOLFILE->set_clear_len | Set file page bytes to be cleared |
| DB_MPOOLFILE->set_fileid | Set file unique identifier |
| DB_MPOOLFILE->set_ftype | Set file type |
| DB_MPOOLFILE->set_lsn_offset | Set file log-sequence-number offset |
| DB_MPOOLFILE->set_pgcookie | Set file cookie for pgin/pgout |
The DB_ENV->memp_fcreate function returns a DB_MPOOLFILE handle on an d29 1 a29 1 the DB_MPOOLFILE->open function. The DB_MPOOLFILE->get function is used to retrieve d31 1 a31 1 returned using the DB_MPOOLFILE->put function. At the time pages are returned, d37 3 a39 3 DB_MPOOLFILE->set function. All dirty pages in the pool from the file may be flushed using the DB_MPOOLFILE->sync function. When the file handle is no longer in use, it should be closed using the DB_MPOOLFILE->close function. d43 1 a43 1
The DB_ENV->memp_fcreate method returns a DB_MPOOLFILE handle on an d28 1 a28 1 the DB_MPOOLFILE->open method. The DB_MPOOLFILE->get method is used to retrieve d30 1 a30 1 returned using the DB_MPOOLFILE->put method. At the time pages are returned, d36 3 a38 3 DB_MPOOLFILE->set method. All dirty pages in the pool from the file may be flushed using the DB_MPOOLFILE->sync method. When the file handle is no longer in use, it should be closed using the DB_MPOOLFILE->close method. d42 1 a42 1
| Memory Pools and Related Methods | Description |
|---|---|
| DB_ENV->set_cachesize | Set the environment cache size |
| DB_ENV->set_mp_mmapsize | Set maximum mapped-in database file size |
| DB_ENV->memp_register | Register input/output functions for a file in a memory pool |
| DB_ENV->memp_stat | Return memory pool statistics |
| DB_ENV->memp_sync | Flush pages from a memory pool |
| DB_ENV->memp_trickle | Trickle flush pages from a memory pool |
| DB_ENV->memp_fcreate | Open a file in a memory pool |
| DB_MPOOLFILE->close | Close a file in a memory pool |
| DB_MPOOLFILE->get | Get page from a file in a memory pool |
| DB_MPOOLFILE->open | Open a file in a memory pool |
| DB_MPOOLFILE->put | Return a page to a memory pool |
| DB_MPOOLFILE->set | Set memory pool page status |
| DB_MPOOLFILE->sync | Flush pages from a file in a memory pool |
| DB_MPOOLFILE->set_clear_len | Set file page bytes to be cleared |
| DB_MPOOLFILE->set_fileid | Set file unique identifier |
| DB_MPOOLFILE->set_ftype | Set file type |
| DB_MPOOLFILE->set_lsn_offset | Set file log-sequence-number offset |
| DB_MPOOLFILE->set_pgcookie | Set file cookie for pgin/pgout |