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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/am_partition.html | |
| parent | 7a2660ba9cc2dc03a69ddfcfd95369395cc87444 (diff) | |
| download | berkeleydb-master.tar.gz | |
Diffstat (limited to 'docs/programmer_reference/am_partition.html')
| -rw-r--r-- | docs/programmer_reference/am_partition.html | 306 |
1 files changed, 156 insertions, 150 deletions
diff --git a/docs/programmer_reference/am_partition.html b/docs/programmer_reference/am_partition.html index e6782175..9bc8879d 100644 --- a/docs/programmer_reference/am_partition.html +++ b/docs/programmer_reference/am_partition.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="am_opensub.html">Prev</a> </td> - <th width="60%" align="center">Chapter 3. - Access Method Operations - </th> + <th width="60%" align="center">Chapter 3. Access Method Operations </th> <td width="20%" align="right"> <a accesskey="n" href="am_get.html">Next</a></td> </tr> </table> @@ -42,136 +40,133 @@ <dl> <dt> <span class="sect2"> - <a href="am_partition.html#am_partition_keys">Specifying partition keys</a> + <a href="am_partition.html#am_partition_keys">Specifying partition + keys</a> </span> </dt> <dt> <span class="sect2"> - <a href="am_partition.html#am_partition_function">Partitioning callback</a> + <a href="am_partition.html#am_partition_function">Partitioning + callback</a> </span> </dt> <dt> <span class="sect2"> - <a href="am_partition.html#partition_file_placement">Placing partition files</a> + <a href="am_partition.html#partition_file_placement">Placing partition + files</a> </span> </dt> </dl> </div> - <p> - You can improve concurrency on your database reads and writes by - splitting access to a single database into multiple databases. This - helps to avoid contention for internal database pages, as well as - allowing you to spread your databases across multiple disks, - which can help to improve disk I/O. -</p> - <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> - <h3 class="title">Note</h3> - <p> - Database partitions are not supported by the C# and Java APIs at - this time. + <p> + You can improve concurrency on your database reads and + writes by splitting access to a single database into multiple + databases. This helps to avoid contention for internal + database pages, as well as allowing you to spread your + databases across multiple disks, which can help to improve + disk I/O. + </p> + <p> + While you can manually do this by creating and using more + than one database for your data, DB is capable of + partitioning your database for you. When you use DB's + built-in database partitioning feature, your access to your + data is performed in exactly the same way as if you were only + using one database; all the work of knowing which database to + use to access a particular record is handled for you under the + hood. + </p> + <p> + Only the BTree and Hash access methods are supported for + partitioned databases. + </p> + <p> + You indicate that you want your database to be partitioned + by calling <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> before opening your database the + first time. You can indicate the directory in which each + partition is contained using the <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> + method. + </p> + <p> + Once you have partitioned a database, you cannot change + your partitioning scheme. + </p> + <p> + There are two ways to indicate what key/data pairs should + go on which partition. The first is by specifying an array of + <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s that indicate the minimum key value for a given + partition. The second is by providing a callback that returns + the number of the partition on which a specified key is + placed. </p> - </div> - <p> - While you can manually do this by creating and using more than one - database for your data, DB is capable of partitioning your - database for you. When you use DB's built-in database partitioning - feature, your access to your data is performed in exactly the same way - as if you were only using one database; all the work of knowing which - database to use to access a particular record is handled for you under - the hood. -</p> - <p> - Only the BTree and Hash access methods are supported for partitioned - databases. -</p> - <p> - You indicate that you want your database to be partitioned by calling - <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> before opening your database the first time. You can - indicate the directory in which each partition is contained using the - <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> method. -</p> - <p> - Once you have partitioned a database, you cannot change your - partitioning scheme. -</p> - <p> - There are two ways to indicate what key/data pairs should go on which - partition. The first is by specifying an array of <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s that indicate - the minimum key value for a given partition. The second is by providing - a callback that returns the number of the partition on which a specified - key is placed. -</p> <div class="sect2" lang="en" xml:lang="en"> <div class="titlepage"> <div> <div> - <h3 class="title"><a id="am_partition_keys"></a>Specifying partition keys</h3> + <h3 class="title"><a id="am_partition_keys"></a>Specifying partition + keys</h3> </div> </div> </div> <p> - For simple cases, you can partition your database by providing - an array of <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s, each element of which provides the minimum - key value to be placed on a partition. There must be one fewer - elements in this array than you have partitions. The first - element of the array indicates the minimum key value for the - second partition in your database. Key values that are less - than the first key value provided in this array are placed on - the first partition (partition 0). + For simple cases, you can partition your database by + providing an array of <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s, each element of which + provides the minimum key value to be placed on a + partition. There must be one fewer elements in this array + than you have partitions. The first element of the array + indicates the minimum key value for the second partition + in your database. Key values that are less than the first + key value provided in this array are placed on the first + partition (partition 0). </p> <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> <h3 class="title">Note</h3> - <p> - You can use partition keys only if you are using the Btree - access method. + <p> + You can use partition keys only if you are using + the Btree access method. </p> </div> <p> - For example, suppose you had a database of fruit, and you want - three partitions for your database. Then you need a <a href="../api_reference/C/dbt.html" class="olink">DBT</a> array - of size two. The first element in this array indicates the - minimum keys that should be placed on partition 1. The second - element in this array indicates the minimum key value placed on - partition 2. Keys that compare less than the first <a href="../api_reference/C/dbt.html" class="olink">DBT</a> in the - array are placed on partition 0. + For example, suppose you had a database of fruit, and + you want three partitions for your database. Then you need + a <a href="../api_reference/C/dbt.html" class="olink">DBT</a> array of size two. The first element in this array + indicates the minimum keys that should be placed on + partition 1. The second element in this array indicates + the minimum key value placed on partition 2. Keys that + compare less than the first <a href="../api_reference/C/dbt.html" class="olink">DBT</a> in the array are placed + on partition 0. </p> - <p> - All comparisons are performed according to the lexicographic - comparison used by your platform. + <p> + All comparisons are performed according to the + lexicographic comparison used by your platform. </p> - <p> - For example, suppose you want all fruits whose names begin - with: + <p> + For example, suppose you want all fruits whose names + begin with: </p> <div class="itemizedlist"> <ul type="disc"> <li> - <p> - 'a' - 'f' to go on partition 0 - </p> + <p> 'a' - 'f' to go on partition 0 </p> </li> <li> - <p> - 'g' - 'p' to go on partition 1 - </p> + <p> 'g' - 'p' to go on partition 1 </p> </li> <li> - <p> - 'q' - 'z' to go on partition 2. - </p> + <p> 'q' - 'z' to go on partition 2. </p> </li> </ul> </div> - <p> + <p> Then you would accomplish this with the following code - fragment: + fragment: </p> <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> <h3 class="title">Note</h3> - <p> - The <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> partition callback parameter must - be <code class="literal">NULL</code> if you are using an array of - <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s to partition your database. + <p> + The <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> partition callback parameter + must be <code class="literal">NULL</code> if you are using an + array of <a href="../api_reference/C/dbt.html" class="olink">DBT</a>s to partition your database. </p> </div> <a id="prog_am10"></a> @@ -225,17 +220,18 @@ <div class="titlepage"> <div> <div> - <h3 class="title"><a id="am_partition_function"></a>Partitioning callback</h3> + <h3 class="title"><a id="am_partition_function"></a>Partitioning + callback</h3> </div> </div> </div> <p> - In some cases, a simple lexicographical comparison of key data - will not sufficiently support a partitioning scheme. For - those situations, you should write a partitioning function. - This function accepts a pointer to the <a href="../api_reference/C/db.html" class="olink">DB</a> and the <a href="../api_reference/C/dbt.html" class="olink">DBT</a>, and - it returns the number of the partition on which the key - belongs. + In some cases, a simple lexicographical comparison of + key data will not sufficiently support a partitioning + scheme. For those situations, you should write a + partitioning function. This function accepts a pointer to + the <a href="../api_reference/C/db.html" class="olink">DB</a> and the <a href="../api_reference/C/dbt.html" class="olink">DBT</a>, and it returns the number of the + partition on which the key belongs. </p> <p> Note that <a href="../api_reference/C/db.html" class="olink">DB</a> actually places the key on the partition @@ -243,12 +239,14 @@ </p> <pre class="programlisting">returned_partition modulo number_of_partitions</pre> <p> - Also, remember that if you use a partitioning function when you - create your database, then you must use the same partitioning - function every time you open that database in the future. + Also, remember that if you use a partitioning function + when you create your database, then you must use the same + partitioning function every time you open that database in + the future. </p> <p> - The following code fragment illustrates a partition callback: + The following code fragment illustrates a partition + callback: </p> <a id="prog_am11"></a> <pre class="programlisting">u_int32_t db_partition_fn(DB *db, DBT *key) { @@ -272,17 +270,17 @@ return ret_number; } </pre> - <p> - You then cause your partition callback to be used by providing it - to the <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> method, as illustrated by the following - code fragment. - </p> + <p> + You then cause your partition callback to be used by + providing it to the <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> method, as + illustrated by the following code fragment. + </p> <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"> <h3 class="title">Note</h3> <p> - The <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> <a href="../api_reference/C/dbt.html" class="olink">DBT</a> array parameter must - be <code class="literal">NULL</code> if you are using a partition - call back to partition your database. + The <a href="../api_reference/C/dbset_partition.html" class="olink">DB->set_partition()</a> <a href="../api_reference/C/dbt.html" class="olink">DBT</a> array parameter must be + <code class="literal">NULL</code> if you are using a + partition call back to partition your database. </p> </div> <a id="prog_am12"></a> @@ -326,66 +324,73 @@ <div class="titlepage"> <div> <div> - <h3 class="title"><a id="partition_file_placement"></a>Placing partition files</h3> + <h3 class="title"><a id="partition_file_placement"></a>Placing partition + files</h3> </div> </div> </div> <p> - When you partition a database, a database file is created on - disk in the same way as if you were not partitioning the - database. That is, this file uses the name you provide to the - <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> <code class="literal">file</code> parameter. + When you partition a database, a database file is + created on disk in the same way as if you were not + partitioning the database. That is, this file uses the + name you provide to the <a href="../api_reference/C/dbopen.html" class="olink">DB->open()</a> <code class="literal">file</code> + parameter. </p> - <p> - However, DB then also creates a series of database files on - disk, one for each partition that you want to use. These - partition files share the same name as the database file name, - but are also number sequentially. So if you create a database - named <code class="filename">mydb.db</code>, and you create 3 partitions - for it, then you will see the following database files on disk: + <p> + However, DB then also creates a series of database + files on disk, one for each partition that you want to + use. These partition files share the same name as the + database file name, but are also number sequentially. So + if you create a database named + <code class="filename">mydb.db</code>, and you create 3 + partitions for it, then you will see the following + database files on disk: </p> <pre class="programlisting"> mydb.db __dbp.mydb.db.000 __dbp.mydb.db.001 __dbp.mydb.db.002 </pre> - <p> - All of the database's contents go into the numbered database - files. You can cause these files to be placed in different - directories (and, hence, different disk partitions or even - disks) by using the <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> method. + <p> + All of the database's contents go into the numbered + database files. You can cause these files to be placed in + different directories (and, hence, different disk + partitions or even disks) by using the + <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> method. </p> - <p> + <p> <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> takes a NULL-terminated array of strings, each one of which should represent an existing filesystem directory. </p> - <p> - If you are using an environment, the directories specified - using <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> must also be included in the - environment list specified by <a href="../api_reference/C/envadd_data_dir.html" class="olink">DB_ENV->add_data_dir()</a>. + <p> + If you are using an environment, the directories + specified using <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> must also be + included in the environment list specified by + <a href="../api_reference/C/envadd_data_dir.html" class="olink">DB_ENV->add_data_dir()</a>. </p> <p> - If you are not using an environment, then the the directories - specified to <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> can be either complete - paths to currently existing directories, or paths relative to - the application's current working directory. + If you are not using an environment, then the the + directories specified to <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> can be + either complete paths to currently existing directories, + or paths relative to the application's current working + directory. </p> - <p> - Ideally, you will provide <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> with an array - that is the same size as the number of partitions you are - creating for your database. Partition files are then placed - according to the order that directories are contained in the - array; partition 0 is placed in directory_array[0], partition 1 - in directory_array[1], and so forth. However, if you provide an - array of directories that is smaller than the number of - database partitions, then the directories are used on a - round-robin fashion. + <p> + Ideally, you will provide <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> with + an array that is the same size as the number of partitions + you are creating for your database. Partition files are + then placed according to the order that directories are + contained in the array; partition 0 is placed in + directory_array[0], partition 1 in directory_array[1], and + so forth. However, if you provide an array of directories + that is smaller than the number of database partitions, + then the directories are used on a round-robin fashion. </p> <p> - You must call <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> before you create your - database, and before you open your database each time - thereafter. The array provided to <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> must not - change after the database has been created. + You must call <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> before you create + your database, and before you open your database each time + thereafter. The array provided to <a href="../api_reference/C/dbset_partition_dirs.html" class="olink">DB->set_partition_dirs()</a> + must not change after the database has been created. </p> </div> </div> @@ -400,7 +405,8 @@ <td width="40%" align="right"> <a accesskey="n" href="am_get.html">Next</a></td> </tr> <tr> - <td width="40%" align="left" valign="top">Opening multiple databases in a single file </td> + <td width="40%" align="left" valign="top">Opening multiple databases in a + single file </td> <td width="20%" align="center"> <a accesskey="h" href="index.html">Home</a> </td> |