1<!--$Id: db_compact.so,v 1.8 2008/04/30 15:25:34 mbrey Exp $--> 2<!--Copyright (c) 1997,2008 Oracle. All rights reserved.--> 3<!--See the file LICENSE for redistribution information.--> 4<html> 5<head> 6<title>Berkeley DB: Db::compact</title> 7<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit."> 8<meta name="keywords" content="embedded,database,programmatic,toolkit,btree,hash,hashing,transaction,transactions,locking,logging,access method,access methods,Java,C,C++"> 9</head> 10<body bgcolor=white> 11<table width="100%"><tr valign=top> 12<td> 13<b>Db::compact</b> 14</td> 15<td align=right> 16<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a> 17<a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a></td> 18</tr></table> 19<hr size=1 noshade> 20<tt> 21<b><pre> 22#include <db_cxx.h> 23<p> 24int 25Db::compact(DbTxn *txnid, 26 Dbt *start, Dbt *stop, DB_COMPACT *c_data, u_int32_t flags, Dbt *end); 27</pre></b> 28<hr size=1 noshade> 29<b>Description: Db::compact</b> 30<p>The Db::compact method compacts Btree and Recno access method 31databases, and optionally returns unused Btree, Hash or Recno database 32pages to the underlying filesystem.</p> 33<p>The Db::compact method 34either returns a non-zero error value 35or throws an exception that encapsulates a non-zero error value on 36failure, and returns 0 on success. 37</p> 38<b>Parameters</b> <br> 39 <b>txnid</b><ul compact><li>If the operation is part of an application-specified transaction, the 40<b>txnid</b> parameter is a transaction handle returned from 41<a href="../api_cxx/txn_begin.html">DbEnv::txn_begin</a>; otherwise NULL. If no transaction handle is 42specified, but the operation occurs in a transactional database, the 43operation will be implicitly transaction protected using multiple 44transactions. These transactions will be periodically committed to 45avoid locking large sections of the tree. Any deadlocks encountered 46cause the compaction operation to retried from the point of the last 47transaction commit.</ul> 48 <b>start</b><ul compact><li>If non-NULL, the <b>start</b> parameter is the starting point for 49compaction in a Btree or Recno database. Compaction will start at the 50smallest key greater than or equal to the specified key. If NULL, 51compaction will start at the beginning of the database.</ul> 52 <b>stop</b><ul compact><li>If non-NULL, the <b>stop</b> parameter is the stopping point for 53compaction in a Btree or Recno database. Compaction will stop at the 54page with the smallest key greater than the specified key. If NULL, 55compaction will stop at the end of the database.</ul> 56 <b>c_data</b><ul compact><li><p>If non-NULL, the <b>c_data</b> parameter contains additional compaction 57configuration parameters, and returns compaction operation statistics, 58in a structure of type DB_COMPACT.</p> 59<p>The following input configuration fields are available from the 60DB_COMPACT structure:</p> 61<br> 62<b>int compact_fillpercent;</b><ul compact><li>If non-zero, the goal for filling pages, specified as a percentage 63between 1 and 100. Any page in a Btree or Recno databases not at or 64above this percentage full will be considered for compaction. The 65default behavior is to consider every page for compaction, regardless 66of its page fill percentage.</ul> 67<b>int compact_pages;</b><ul compact><li>If non-zero, the call will return after that number of pages have been 68freed.</ul> 69<b>db_timeout_t compact_timeout;</b><ul compact><li>If non-zero, and no <b>txnid</b> parameter was specified, the lock 70timeout set for implicit transactions, in microseconds.</ul> 71<br> 72<p>The following output statistics fields are available from the 73DB_COMPACT structure:</p> 74<br> 75<b>u_int32_t compact_deadlock;</b><ul compact><li>An output statistics parameter: if no <b>txnid</b> parameter was 76specified, the number of deadlocks which occurred.</ul> 77<b>u_int32_t compact_pages_examine;</b><ul compact><li>An output statistics parameter: the number of database pages reviewed 78during the compaction phase.</ul> 79<b>u_int32_t compact_pages_free;</b><ul compact><li>An output statistics parameter: the number of database pages freed during 80the compaction phase.</ul> 81<b>u_int32_t compact_levels;</b><ul compact><li>An output statistics parameter: the number of levels removed from the 82Btree or Recno database during the compaction phase.</ul> 83<b>u_int32_t compact_pages_truncated;</b><ul compact><li>An output statistics parameter: the number of database pages returned 84to the filesystem.</ul> 85<br></ul> 86 <b>flags</b><ul compact><li>The <b>flags</b> parameter must be set to 0 or 87one of the following values: 88<br> 89<b><a name="DB_FREELIST_ONLY">DB_FREELIST_ONLY</a></b><ul compact><li>Do no page compaction, only returning pages to the filesystem that are 90already free and at the end of the file. This flag must be set if the 91database is a Hash access method database.</ul> 92<b><a name="DB_FREE_SPACE">DB_FREE_SPACE</a></b><ul compact><li>Return pages to the filesystem when possible. 93If this flag is not specified, pages emptied as a result of compaction 94will be placed on the free list for re-use, but never returned to the 95filesystem. 96<p>Note that only pages at the end of a file can be returned to the 97filesystem. Because of the one-pass nature of the compaction algorithm, 98any not emptied page near the end of the file inhibits returning pages to 99the file system. A repeated call to the Db::compact method with a low 100<b>compact_fillpercent</b> may be used to return pages in this case.</p></ul> 101<br></ul> 102 <b>end</b><ul compact><li>If non-NULL, the <b>end</b> parameter will be filled in with the 103database key marking the end of the compaction operation in a Btree or 104Recno database. This is generally the first key of the page where the 105operation stopped.</ul> 106<br> 107<br><b>Errors</b> 108<p>The Db::compact method 109may fail and throw 110<a href="../api_cxx/except_class.html">DbException</a>, 111encapsulating one of the following non-zero errors, or return one of 112the following non-zero errors:</p> 113<br> 114<b>DB_REP_HANDLE_DEAD</b><ul compact><li>The database handle has been invalidated because a replication election 115unrolled a committed transaction.</ul> 116<br> 117<br> 118<b>DB_REP_LOCKOUT</b><ul compact><li>The operation was blocked by client/master synchronization.</ul> 119<br> 120<br> 121<b>EACCES</b><ul compact><li>An attempt was made to modify a read-only database.</ul> 122<br> 123<br> 124<b>EINVAL</b><ul compact><li>An 125invalid flag value or parameter was specified.</ul> 126<br> 127<p>If a transactional database environment operation was selected to 128resolve a deadlock, the Db::compact method will fail and 129either return <a href="../ref/program/errorret.html#DB_LOCK_DEADLOCK">DB_LOCK_DEADLOCK</a> or 130throw a <a href="../api_cxx/deadlock_class.html">DbDeadlockException</a> exception.</p> 131<p>If a Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable 132to grant a lock in the allowed time, the Db::compact method will fail and 133either return <a href="../ref/program/errorret.html#DB_LOCK_NOTGRANTED">DB_LOCK_NOTGRANTED</a> or 134throw a <a href="../api_cxx/lockng_class.html">DbLockNotGrantedException</a> exception.</p> 135<hr size=1 noshade> 136<br><b>Class</b> 137<a href="../api_cxx/db_class.html">Db</a> 138<br><b>See Also</b> 139<a href="../api_cxx/db_list.html">Databases and Related Methods</a> 140</tt> 141<table width="100%"><tr><td><br></td><td align=right> 142<a href="../api_cxx/api_core.html"><img src="../images/api.gif" alt="API"></a><a href="../ref/toc.html"><img src="../images/ref.gif" alt="Ref"></a> 143</td></tr></table> 144<p><font size=1>Copyright (c) 1996,2008 Oracle. 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