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<title>Berkeley DB Reference Guide: Reviewing Berkeley DB log files</title>
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<meta name="description" content="Berkeley DB: An embedded database programmatic toolkit.">
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<table width="100%"><tr valign=top>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Debugging Applications</dl></h3></td>
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<td align=right><a href="../../ref/debug/runtime.html"><img src="../../images/prev.gif" alt="Prev"></a><a href="../../reftoc.html"><img src="../../images/ref.gif" alt="Ref"></a><a href="../../ref/debug/common.html"><img src="../../images/next.gif" alt="Next"></a>
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<h1 align=center>Reviewing Berkeley DB log files</h1>
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<p>If you are running with transactions and logging, the <a href="../../utility/db_printlog.html">db_printlog</a>
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utility can be a useful debugging aid. The <a href="../../utility/db_printlog.html">db_printlog</a> utility
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will display the contents of your log files in a human readable (and
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machine-processable) format.
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<p>The <a href="../../utility/db_printlog.html">db_printlog</a> utility will attempt to display any and all
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log files present in a designated db_home directory. For each log record,
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<a href="../../utility/db_printlog.html">db_printlog</a> will display a line of the form:
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<p><blockquote><pre>[22][28]db_big: rec: 43 txnid 80000963 prevlsn [21][10483281]</pre></blockquote>
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<p>The opening numbers in square brackets are the <i>log sequence
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number</i> (<i>LSN</i>) of the log record being displayed. The first
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number indicates the log file in which the record appears, and the
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second number indicates the offset in that file of the record.
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<p>The first character string identifies the particular log operation being
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reported. The log records corresponding to particular operations are
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described following. The rest of the line consists of name/value pairs.
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<p>The rec field indicates the record type (this is used to dispatch records
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in the log to appropriate recovery functions).
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<p>The txnid field identifies the transaction for which this record was
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written. A txnid of 0 means that the record was written outside the
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context of any transaction. You will see these most frequently for
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<p>Finally, the prevlsn contains the LSN of the last record for this
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transaction. By following prevlsn fields, you can accumulate all the
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updates for a particular transaction. During normal abort processing,
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this field is used to quickly access all the records for a particular
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<p>After the initial line identifying the record type, each field of the log
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record is displayed, one item per line. There are several fields that
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appear in many different records and a few fields that appear only in
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<p>The following table presents each currently written log record type with
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a brief description of the operation it describes.
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<!--START LOG RECORD TYPES-->
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<tr><th>Log Record Type</th><th>Description</th></tr>
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<tr><td>bam_adj</td><td>Used when we insert/remove an index into/from the page header of a Btree page.</td></tr>
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<tr><td>bam_cadjust</td><td>Keeps track of record counts in a Btree or Recno database.</td></tr>
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<tr><td>bam_cdel</td><td>Used to mark a record on a page as deleted.</td></tr>
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<tr><td>bam_curadj</td><td>Used to adjust a cursor location when a nearby record changes in a Btree database.</td></tr>
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<tr><td>bam_pg_alloc</td><td>Indicates that we allocated a page to a Btree.</td></tr>
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<tr><td>bam_pg_free</td><td>Indicates that we freed a page in the Btree (freed pages are added to a freelist and reused).</td></tr>
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<tr><td>bam_rcuradj</td><td>Used to adjust a cursor location when a nearby record changes in a Recno database.</td></tr>
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<tr><td>bam_repl</td><td>Describes a replace operation on a record.</td></tr>
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<tr><td>bam_root</td><td>Describes an assignment of a root page.</td></tr>
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<tr><td>bam_rsplit</td><td>Describes a reverse page split.</td></tr>
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<tr><td>bam_split</td><td>Describes a page split.</td></tr>
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<tr><td>crdel_delete</td><td>Describes the removal of a Berkeley DB file.</td></tr>
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<tr><td>crdel_fileopen</td><td>Describes a Berkeley DB file create attempt.</td></tr>
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<tr><td>crdel_metapage</td><td>Describes the creation of a metadata page for a new file.</td></tr>
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<tr><td>crdel_metasub</td><td>Describes the creation of a metadata page for a subdatabase.</td></tr>
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<tr><td>crdel_rename</td><td>Describes a file rename operation.</td></tr>
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<tr><td>db_addrem</td><td>Add or remove an item from a page of duplicates.</td></tr>
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<tr><td>db_big</td><td>Add an item to an overflow page (<i>overflow pages</i> contain items too large to place on the main page)</td></tr>
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<tr><td>db_debug</td><td>Log debugging message.</td></tr>
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<tr><td>db_noop</td><td>This marks an operation that did nothing but update the LSN on a page.</td></tr>
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<tr><td>db_ovref</td><td>Increment or decrement the reference count for a big item.</td></tr>
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<tr><td>db_relink</td><td>Fix prev/next chains on duplicate pages because a page was added or removed.</td></tr>
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<tr><td>ham_chgpg</td><td>Used to adjust a cursor location when a Hash page is removed, and its elements are moved to a different Hash page.</td></tr>
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<tr><td>ham_copypage</td><td>Used when we empty a bucket page, but there are overflow pages for the bucket; one needs to be copied back into the actual bucket.</td></tr>
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<tr><td>ham_curadj</td><td>Used to adjust a cursor location when a nearby record changes in a Hash database.</td></tr>
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<tr><td>ham_groupalloc</td><td>Allocate some number of contiguous pages to the Hash database.</td></tr>
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<tr><td>ham_insdel</td><td>Insert/delete an item on a Hash page.</td></tr>
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<tr><td>ham_metagroup</td><td>Update the metadata page to reflect the allocation of a sequence of contiguous pages.</td></tr>
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<tr><td>ham_newpage</td><td>Adds or removes overflow pages from a Hash bucket.</td></tr>
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<tr><td>ham_replace</td><td>Handle updates to records that are on the main page.</td></tr>
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<tr><td>ham_splitdata</td><td>Record the page data for a split.</td></tr>
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<tr><td>log_register</td><td>Records an open of a file (mapping the filename to a log-id that is used in subsequent log operations).</td></tr>
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<tr><td>qam_add</td><td>Describes the actual addition of a new record to a Queue.</td></tr>
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<tr><td>qam_del</td><td>Delete a record in a Queue.</td></tr>
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<tr><td>qam_delext</td><td>Delete a record in a Queue with extents.</td></tr>
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<tr><td>qam_delete</td><td>Remove a Queue extent file.</td></tr>
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<tr><td>qam_incfirst</td><td>Increments the record number that refers to the first record in the database.</td></tr>
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<tr><td>qam_mvptr</td><td>Indicates that we changed the reference to either or both of the first and current records in the file.</td></tr>
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<tr><td>qam_rename</td><td>Rename a Queue extent file.</td></tr>
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<tr><td>txn_child</td><td>Commit a child transaction.</td></tr>
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<tr><td>txn_ckp</td><td>Transaction checkpoint.</td></tr>
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<tr><td>txn_regop</td><td>Logs a regular (non-child) transaction commit.</td></tr>
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<tr><td>txn_xa_regop</td><td>Logs a prepare message.</td></tr>
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<!--END LOG RECORD TYPES-->
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<h3>Augmenting the Log for Debugging</h3>
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<p>When debugging applications, it is sometimes useful to log not only the
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actual operations that modify pages, but also the underlying Berkeley DB
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functions being executed. This form of logging can add significant bulk
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to your log, but can permit debugging application errors that are almost
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impossible to find any other way. To turn on these log messages, specify
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the --enable-debug_rop and --enable-debug_wop configuration options when
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configuring Berkeley DB. See <a href="../../ref/build_unix/conf.html">Configuring
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Berkeley DB</a> for more information.
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<h3>Extracting Committed Transactions and Transaction Status</h3>
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<p>Sometimes, it is helpful to use the human-readable log output to
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determine which transactions committed and aborted. The awk script,
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commit.awk, (found in the db_printlog directory of the Berkeley DB
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distribution) allows you to do just that. The following command,
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where log_output is the output of db_printlog, will display a list of
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the transaction IDs of all committed transactions found in the log:
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<p><blockquote><pre>awk -f commit.awk log_output</pre></blockquote>
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<p>If you need a complete list of both committed and aborted transactions,
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then the script status.awk will produce it. The syntax is as follows:
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<p><blockquote><pre>awk -f status.awk log_output</pre></blockquote>
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<h3>Extracting Transaction Histories</h3>
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<p>Another useful debugging aid is to print out the complete history of a
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transaction. The awk script txn.awk allows you to do that. The
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following command line, where log_output is the output of
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<a href="../../utility/db_printlog.html">db_printlog</a> and txnlist is a comma-separated list of transaction
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IDs, will display all log records associated with the designated
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<p><blockquote><pre>awk -f txn.awk TXN=txnlist log_output</pre></blockquote>
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<h3>Extracting File Histories</h3>
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<p>The awk script fileid.awk allows you to extract all log records that
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refer to a designated file. The syntax for the fileid.awk script is
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the following, where log_output is the output of db_printlog and fids
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is a comma-separated list of fileids:
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<p><blockquote><pre>awk -f fileid.awk PGNO=fids log_output</pre></blockquote>
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<h3>Extracting Page Histories</h3>
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<p>The awk script pgno.awk allows you to extract all log records that refer
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to designated page numbers. However, because this script will extract
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records with the designated page numbers for all files, it is most
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useful in conjunction with the fileid script. The syntax for the
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pgno.awk script is the following, where log_output is the output of
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db_printlog and pgnolist is a comma-separated list of page numbers:
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<p><blockquote><pre>awk -f pgno.awk PGNO=pgnolist log_output</pre></blockquote>
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<h3>Other log processing tools</h3>
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<p>The awk script count.awk prints out the number of log records
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encountered that belonged to some transaction (that is, the number of
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log records excluding those for checkpoints and
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non-transaction-protected operations).
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<p>The script range.awk will extract a subset of a log. This is useful
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when the output of <a href="../../utility/db_printlog.html">db_printlog</a> is too large to be reasonably
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manipulated with an editor or other tool. The syntax for range.awk is
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the following, where <b>sf</b> and <b>so</b> represent the LSN
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of the beginning of the sublog you want to extract, and <b>ef</b> and
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<b>eo</b> represent the LSN of the end of the sublog you want to
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<p><blockquote><pre>awk -f range.awk START_FILE=sf START_OFFSET=so END_FILE=ef END_OFFSET=eo log_output</pre></blockquote>
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