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| author | Lorry Tar Creator <lorry-tar-importer@baserock.org> | 2015-02-17 17:25:57 +0000 |
|---|---|---|
| committer | <> | 2015-03-17 16:26:24 +0000 |
| commit | 780b92ada9afcf1d58085a83a0b9e6bc982203d1 (patch) | |
| tree | 598f8b9fa431b228d29897e798de4ac0c1d3d970 /docs/programmer_reference/mp_config.html | |
| parent | 7a2660ba9cc2dc03a69ddfcfd95369395cc87444 (diff) | |
| download | berkeleydb-master.tar.gz | |
Diffstat (limited to 'docs/programmer_reference/mp_config.html')
| -rw-r--r-- | docs/programmer_reference/mp_config.html | 111 |
1 files changed, 60 insertions, 51 deletions
diff --git a/docs/programmer_reference/mp_config.html b/docs/programmer_reference/mp_config.html index ae7083aa..1c585e4b 100644 --- a/docs/programmer_reference/mp_config.html +++ b/docs/programmer_reference/mp_config.html @@ -14,7 +14,7 @@ <body> <div xmlns="" class="navheader"> <div class="libver"> - <p>Library Version 11.2.5.3</p> + <p>Library Version 12.1.6.1</p> </div> <table width="100%" summary="Navigation header"> <tr> @@ -22,9 +22,7 @@ </tr> <tr> <td width="20%" align="left"><a accesskey="p" href="mp.html">Prev</a> </td> - <th width="60%" align="center">Chapter 18. - The Memory Pool Subsystem - </th> + <th width="60%" align="center">Chapter 18. The Memory Pool Subsystem </th> <td width="20%" align="right"> <a accesskey="n" href="mp_warm.html">Next</a></td> </tr> </table> @@ -38,52 +36,65 @@ </div> </div> </div> - <p>There are two issues to consider when configuring the memory pool.</p> - <p>The first issue, the most important tuning parameter for Berkeley DB -applications, is the size of the memory pool. There are two ways to -specify the pool size. First, calling the <a href="../api_reference/C/envset_cachesize.html" class="olink">DB_ENV->set_cachesize()</a> method -specifies the pool size for all of the applications sharing the Berkeley DB -environment. Second, the <a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> method only specifies a -pool size for the specific database. Note: It is meaningless to call -<a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> for a database opened inside of a Berkeley DB -environment because the environment pool size will override any pool -size specified for a single database. For information on tuning the -Berkeley DB cache size, see -<a class="xref" href="general_am_conf.html#am_conf_cachesize" title="Selecting a cache size">Selecting a cache size</a>.</p> <p> - Note the memory pool defaults to assuming that the average page size is - 4k. This factor is used to determine the size of the hash table used - to locate pages in the memory pool. The size of the hash table is - calculated to so that on average 2.5 pages will be in each hash table - entry. Each page requires a mutex be allocated to it and the average - page size is used to determine the number of mutexes to allocate to the - memory pool. -</p> + There are two issues to consider when configuring the memory + pool. + </p> <p> - Normally you should see good results by using the default values for - the page size, but in some cases you may be able to achieve better - performance by manually configuring the page size. The expected page - size, hash table size and mutex count can be set via the methods: - <a href="../api_reference/C/envset_mp_pagesize.html" class="olink">DB_ENV->set_mp_pagesize()</a>, <a href="../api_reference/C/envset_mp_tablesize.html" class="olink">DB_ENV->set_mp_tablesize()</a>, and <a href="../api_reference/C/envset_mp_mtxcount.html" class="olink">DB_ENV->set_mp_mtxcount()</a>. -</p> - <p>The second memory pool configuration issue is the maximum size an -underlying file can be and still be mapped into the process address -space (instead of reading the file's pages into the cache). Mapping -files into the process address space can result in better performance -because available virtual memory is often much larger than the local -cache, and page faults are faster than page copying on many systems. -However, in the presence of limited virtual memory, it can cause -resource starvation; and in the presence of large databases, it can -result in immense process sizes. In addition, because of the -requirements of the Berkeley DB transactional implementation, only read-only -files can be mapped into process memory.</p> - <p>To specify that no files are to be mapped into the process address -space, specify the <a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the -<a href="../api_reference/C/envset_flags.html" class="olink">DB_ENV->set_flags()</a> method. To specify that any individual file should -not be mapped into the process address space, specify the -<a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the <a href="../api_reference/C/mempfopen.html" class="olink">DB_MPOOLFILE->open()</a> interface. To limit -the size of files mapped into the process address space, use the -<a href="../api_reference/C/envset_mp_mmapsize.html" class="olink">DB_ENV->set_mp_mmapsize()</a> method.</p> + The first issue, the most important tuning parameter for + Berkeley DB applications, is the size of the memory pool. + There are two ways to specify the pool size. First, calling + the <a href="../api_reference/C/envset_cachesize.html" class="olink">DB_ENV->set_cachesize()</a> method specifies the pool size for all + of the applications sharing the Berkeley DB environment. + Second, the <a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> method only specifies a pool + size for the specific database. Note: It is meaningless to + call <a href="../api_reference/C/dbset_cachesize.html" class="olink">DB->set_cachesize()</a> for a database opened inside of a + Berkeley DB environment because the environment pool size will + override any pool size specified for a single database. For + information on tuning the Berkeley DB cache size, see <a class="xref" href="general_am_conf.html#am_conf_cachesize" title="Selecting a cache size">Selecting a cache size</a>. + </p> + <p> + Note the memory pool defaults to assuming that the average + page size is 4k. This factor is used to determine the size of + the hash table used to locate pages in the memory pool. The + size of the hash table is calculated to so that on average 2.5 + pages will be in each hash table entry. Each page requires a + mutex be allocated to it and the average page size is used to + determine the number of mutexes to allocate to the memory + pool. + </p> + <p> + Normally you should see good results by using the default + values for the page size, but in some cases you may be able to + achieve better performance by manually configuring the page + size. The expected page size, hash table size and mutex count + can be set via the methods: <a href="../api_reference/C/envset_mp_pagesize.html" class="olink">DB_ENV->set_mp_pagesize()</a>, + <a href="../api_reference/C/envset_mp_tablesize.html" class="olink">DB_ENV->set_mp_tablesize()</a>, and <a href="../api_reference/C/envset_mp_mtxcount.html" class="olink">DB_ENV->set_mp_mtxcount()</a>. + </p> + <p> + The second memory pool configuration issue is the maximum + size an underlying file can be and still be mapped into the + process address space (instead of reading the file's pages + into the cache). Mapping files into the process address space + can result in better performance because available virtual + memory is often much larger than the local cache, and page + faults are faster than page copying on many systems. However, + in the presence of limited virtual memory, it can cause + resource starvation; and in the presence of large databases, + it can result in immense process sizes. In addition, because + of the requirements of the Berkeley DB transactional + implementation, only read-only files can be mapped into + process memory. + </p> + <p> + To specify that no files are to be mapped into the process + address space, specify the <a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the + <a href="../api_reference/C/envset_flags.html" class="olink">DB_ENV->set_flags()</a> method. To specify that any individual file + should not be mapped into the process address space, specify + the <a href="../api_reference/C/dbopen.html#open_DB_NOMMAP" class="olink">DB_NOMMAP</a> flag to the <a href="../api_reference/C/mempfopen.html" class="olink">DB_MPOOLFILE->open()</a> interface. To limit + the size of files mapped into the process address space, use + the <a href="../api_reference/C/envset_mp_mmapsize.html" class="olink">DB_ENV->set_mp_mmapsize()</a> method. + </p> </div> <div class="navfooter"> <hr /> @@ -96,9 +107,7 @@ the size of files mapped into the process address space, use the <td width="40%" align="right"> <a accesskey="n" href="mp_warm.html">Next</a></td> </tr> <tr> - <td width="40%" align="left" valign="top">Chapter 18. - The Memory Pool Subsystem - </td> + <td width="40%" align="left" valign="top">Chapter 18. The Memory Pool Subsystem </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> |