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<!--$Id: printlog.so,v 10.20 2000/12/01 20:15:25 bostic Exp $-->
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<title>Berkeley DB Reference Guide: Reviewing Berkeley DB log files</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Debugging Applications</dl></h3></td>
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<p>
<h1 align=center>Reviewing Berkeley DB log files</h1>
<p>If you are running with transactions and logging, the <a href="../../utility/db_printlog.html">db_printlog</a>
utility can be a useful debugging aid. The <a href="../../utility/db_printlog.html">db_printlog</a> utility
will display the contents of your log files in a human readable (and
machine-processable) format.
<p>The <a href="../../utility/db_printlog.html">db_printlog</a> utility will attempt to display any and all
logfiles present in a designated db_home directory. For each log record,
<a href="../../utility/db_printlog.html">db_printlog</a> will display a line of the form:
<p><blockquote><pre>[22][28]db_big: rec: 43 txnid 80000963 prevlsn [21][10483281]</pre></blockquote>
<p>The opening numbers in square brackets are the log sequence number (LSN)
of the log record being displayed. The first number indicates the log
file in which the record appears, and the second number indicates the
offset in that file of the record.
<p>The first character string identifies the particular log operation being
reported. The log records corresponding to particular operations are
described below. The rest of the line consists of name/value pairs.
<p>The rec field indicates the record type (this is used to dispatch records
in the log to appropriate recovery functions).
<p>The txnid field identifies the transaction for which this record was
written. A txnid of 0 means that the record was written outside the
context of any transaction. You will see these most frequently for
checkpoints.
<p>Finally, the prevlsn contains the LSN of the last record for this
transaction. By following prevlsn fields, you can accumulate all the
updates for a particular transaction. During normal abort processing,
this field is used to quickly access all the records for a particular
transaction.
<p>After the initial line identifying the record type, each field of the log
record is displayed, one item per line. There are several fields that
appear in many different records and a few fields that appear only in
some records.
<p>The list below presents each log record type currently produced with a brief
description of the operation they describe.
<!--START LOG RECORD TYPES-->
<p><table border=1>
<tr><th>Log Record Type</th><th>Description</th></tr>
<tr><td>bam_adj</td><td>Used when we insert/remove an index into/from the page header of a Btree page.</td></tr>
<tr><td>bam_cadjust</td><td>Keeps track of record counts in a Btree or Recno database.</td></tr>
<tr><td>bam_cdel</td><td>Used to mark a record on a page as deleted.</td></tr>
<tr><td>bam_curadj</td><td>Used to adjust a cursor location when a nearby record changes in a Btree database.</td></tr>
<tr><td>bam_pg_alloc</td><td>Indicates that we allocated a page to a Btree.</td></tr>
<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>
<tr><td>bam_rcuradj</td><td>Used to adjust a cursor location when a nearby record changes in a Recno database.</td></tr>
<tr><td>bam_repl</td><td>Describes a replace operation on a record.</td></tr>
<tr><td>bam_root</td><td>Describes an assignment of a root page.</td></tr>
<tr><td>bam_rsplit</td><td>Describes a reverse page split.</td></tr>
<tr><td>bam_split</td><td>Describes a page split.</td></tr>
<tr><td>crdel_delete</td><td>Describes the removal of a Berkeley DB file.</td></tr>
<tr><td>crdel_fileopen</td><td>Describes a Berkeley DB file create attempt.</td></tr>
<tr><td>crdel_metapage</td><td>Describes the creation of a meta-data page for a new file.</td></tr>
<tr><td>crdel_metasub</td><td>Describes the creation of a meta data page for a subdatabase.</td></tr>
<tr><td>crdel_rename</td><td>Describes a file rename operation.</td></tr>
<tr><td>db_addrem</td><td>Add or remove an item from a page of duplicates.</td></tr>
<tr><td>db_big</td><td>Add an item to an overflow page (overflow pages contain items too large to place on the main page)</td></tr>
<tr><td>db_debug</td><td>Log debugging message.</td></tr>
<tr><td>db_noop</td><td>This marks an operation that did nothing but update the LSN on a page.</td></tr>
<tr><td>db_ovref</td><td>Increment or decrement the reference count for a big item.</td></tr>
<tr><td>db_relink</td><td>Fix prev/next chains on duplicate pages because a page was added or removed.</td></tr>
<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>
<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>
<tr><td>ham_curadj</td><td>Used to adjust a cursor location when a nearby record changes in a Hash database.</td></tr>
<tr><td>ham_groupalloc</td><td>Allocate some number of contiguous pages to the Hash database.</td></tr>
<tr><td>ham_insdel</td><td>Insert/Delete an item on a Hash page.</td></tr>
<tr><td>ham_metagroup</td><td>Update the metadata page to reflect the allocation of a sequence of contiguous pages.</td></tr>
<tr><td>ham_newpage</td><td>Adds or removes overflow pages from a Hash bucket.</td></tr>
<tr><td>ham_replace</td><td>Handle updates to records that are on the main page.</td></tr>
<tr><td>ham_splitdata</td><td>Record the page data for a split.</td></tr>
<tr><td>log_register</td><td>Records an open of a file (mapping the file name to a log-id that is used in subsequent log operations).</td></tr>
<tr><td>qam_add</td><td>Describes the actual addition of a new record to a Queue.</td></tr>
<tr><td>qam_del</td><td>Delete a record in a Queue.</td></tr>
<tr><td>qam_delete</td><td>Remove a Queue extent file.</td></tr>
<tr><td>qam_inc</td><td>Increments the maximum record number allocated in a Queue indicating that we've allocated another space in the file.</td></tr>
<tr><td>qam_incfirst</td><td>Increments the record number that refers to the first record in the database.</td></tr>
<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>
<tr><td>qam_rename</td><td>Rename a Queue extent file.</td></tr>
<tr><td>txn_child</td><td>Commit a child transaction.</td></tr>
<tr><td>txn_ckp</td><td>Transaction checkpoint.</td></tr>
<tr><td>txn_regop</td><td>Logs a regular (non-child) transaction commit.</td></tr>
<tr><td>txn_xa_regop</td><td>Logs a prepare message.</td></tr>
</table>
<!--END LOG RECORD TYPES-->
<h3>Augmenting the Log for Debugging</h3>
<p>When debugging applications, it is sometimes useful to log, not only the
actual operations that modify pages, but also the underlying Berkeley DB
functions being executed. This form of logging can add significant bulk
to your log, but can permit debugging application errors that are almost
impossible to find any other way. To turn on these log messages, specify
the --enable-debug_rop and --enable-debug_wop configuration options when
configuring Berkeley DB. See <a href="../../ref/build_unix/conf.html">Configuring
Berkeley DB</a> for more information.
<h3>Extracting Committed Transactions and Transaction Status</h3>
<p>Sometimes it is useful to use the human-readable log output to determine
which transactions committed and aborted. The awk script, commit.awk,
found in the db_printlog directory of the Berkeley DB distribution allows you
to do just that. The command:
<p><blockquote><pre>awk -f commit.awk log_output</pre></blockquote>
where log_output is the output of db_printlog will display a list of
the transaction IDs of all committed transactions found in the log.
<p>If you need a complete list of both committed and aborted transactions,
then the script status.awk will produce that. The syntax is:
<p><blockquote><pre>awk -f status.awk log_output</pre></blockquote>
<h3>Extracting Transaction Histories</h3>
<p>Another useful debugging aid is to print out the complete history of a
transaction. The awk script txn.awk, allows you to do that. The
command line:
<p><blockquote><pre>awk -f txn.awk TXN=txnlist log_output</pre></blockquote>
where log_output is the output of <a href="../../utility/db_printlog.html">db_printlog</a> and txnlist is
a comma-separated list of transaction IDs, will display all log records
associated with the designated transaction ids.
<h3>Extracting File Histories</h3>
<p>The awk script fileid.awk, allows you to extract all log records that
affect particular files. The syntax for the fileid.awk script is:
<p><blockquote><pre>awk -f fileid.awk PGNO=fids log_output</pre></blockquote>
<p>where log_output is the output of db_printlog and fids is a
comma-separated list of fileids. The script will output all log
records that reference the designated file.
<h3>Extracting Page Histories</h3>
<p>The awk script pgno.awk, allows you to extract all log records that
affect particular pages. As currently designed, however, it will
extract records of all files with the designated page number, so this
script is most useful in conjunction with the fileid script. The syntax
for the pgno.awk script is:
<p><blockquote><pre>awk -f pgno.awk PGNO=pgnolist log_output</pre></blockquote>
<p>where log_output is the output of db_printlog and pgnolist is a
comma-separated list of page numbers. The script will output all log
records that reference the designated page numbers.
<h3>Other log processing tools</h3>
<p>The awk script count.awk will print out the number of log records
encountered that belonged to some transaction (that is the number of log
records excluding those for checkpoints and non-transaction protected
operations).
<p>The script range.awk will extract a subset of a log. This is useful
when the output of <a href="../../utility/db_printlog.html">db_printlog</a> is too large to be reasonably
manipulated with an editor or other tool.
<p>The syntax for range.awk is:
<p><blockquote><pre>awk -f range.awk START_FILE=sf START_OFFSET=so END_FILE=ef END_OFFSET=eo log_output</pre></blockquote>
<p>where the <b>sf</b> and <b>so</b> represent the log sequence number
(LSN) of the beginning of the sublog you wish to extract and <b>ef</b>
and <b>eo</b> represent the LSN of the end of the sublog you wish to
extract.
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