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<h1 class="topictitle1">Commitment control</h1>
<div><p>The <span class="keyword">DB2<sup>®</sup> UDB for iSeries™</span> commitment
control support provides a means to process a group of database changes like
update, insert, DDL, or delete operations as a single unit of work (transaction).</p>
<div class="section"><p>A commit operation guarantees that the group of operations is
completed. A rollback operation guarantees that the group of operations is
backed out. A savepoint can be used to break a transaction into smaller units
that can be rolled back. A commit operation can be issued through several
different interfaces. For example,</p>
<ul><li>An SQL COMMIT statement</li>
<li>A CL COMMIT command</li>
<li>A language commit statement (such as an RPG COMMIT statement)</li>
</ul>
<p> A rollback operation can be issued through several different interfaces.
For example,</p>
<ul><li>An SQL ROLLBACK statement</li>
<li>A CL ROLLBACK command</li>
<li>A language rollback statement (such as an RPG ROLBK statement)</li>
</ul>
</div>
<div class="section"><p>The only SQL statements that cannot be committed or rolled back
are: </p>
<ul><li>DROP SCHEMA</li>
<li>GRANT or REVOKE if an authority holder exists for the specified object</li>
</ul>
</div>
<div class="section"><p>If commitment control was not already started when either an SQL
statement is executed with an isolation level other than COMMIT(*NONE) or
a RELEASE statement is executed, then <span class="keyword">DB2 UDB for iSeries</span> sets
up the commitment control environment by implicitly calling the CL command
Start Commitment Control (STRCMTCTL). <span class="keyword">DB2 UDB for iSeries</span> specifies
NFYOBJ(*NONE) and CMTSCOPE(*ACTGRP) parameters along with LCKLVL on the STRCMTCTL
command. The LCKLVL specified is the lock level on the COMMIT parameter on
the CRTSQLxxx, STRSQL, or RUNSQLSTM commands. In REXX, the LCKLVL specified
is the lock level on the SET OPTION statement. You may use the STRCMTCTL command
to specify a different CMTSCOPE, NFYOBJ, or LCKLVL. If you specify CMTSCOPE(*JOB)
to start the job level commitment definition, <span class="keyword">DB2 UDB for iSeries</span> uses
the job level commitment definition for programs in that activation group.
</p>
<div class="note"><span class="notetitle">Notes:</span> <ol><li>When using commitment control, the tables referred to in the application
program by Data Manipulation Language statements must be journaled.</li>
<li>Note that the LCKLVL specified is only the default lock level. After commitment
control is started, the SET TRANSACTION SQL statement and the lock level specified
on the COMMIT parameter on the CRTSQLxxx, STRSQL, or RUNSQLSTM commands will
override the default lock level.</li>
</ol>
</div>
</div>
<div class="section"><div class="p">For cursors that use column functions, GROUP BY, or HAVING, and
are running under commitment control, a ROLLBACK HOLD has no effect on the
cursor's position. In addition, the following occurs under commitment control: <ul><li>If COMMIT(*CHG) and (ALWBLK(*NO) or (ALWBLK(*READ)) is specified for one
of these cursors, a message (CPI430B) is sent that says COMMIT(*CHG) requested
but not allowed.</li>
<li>If COMMIT(*ALL), COMMIT(*RR), or COMMIT(*CS) with the KEEP LOCKS clause
is specified for one of the cursors, <span class="keyword">DB2 UDB for iSeries</span> will
lock all referenced tables in shared mode (*SHRNUP). The lock prevents concurrent
application processes from executing any but read-only operations on the named
table. A message (either SQL7902 or CPI430A) is sent that says COMMIT(*ALL),
COMMIT(*RR), or COMMIT(*CS) with the KEEP LOCKS clause is specified for one
of the cursors requested but not allowed. Message SQL0595 may also be sent.</li>
</ul>
</div>
</div>
<div class="section"><p>For cursors where either COMMIT(*ALL), COMMIT(*RR), or COMMIT(*CS)
with the KEEP LOCKS clause is specified and either catalog files are used
or a temporary result table is required, <span class="keyword">DB2 UDB for iSeries</span> will
lock all referenced tables in shared mode (*SHRNUP). This will prevent concurrent
processes from executing anything but read-only operations on the table(s).
A message (either SQL7902 or CPI430A) is sent that says COMMIT(*ALL) is requested
but not allowed. Message SQL0595 may also be sent.</p>
</div>
<div class="section"><p>If ALWBLK(*ALLREAD) and COMMIT(*CHG) were specified, when the
program was precompiled, all read-only cursors will allow blocking of rows
and a ROLLBACK HOLD will not roll the cursor position back.</p>
</div>
<div class="section"><p>If COMMIT(*RR) is requested, the tables will be locked until the
query is closed. If the cursor is read-only, the table will be locked (*SHRNUP).
If the cursor is in update mode, the table will be locked (*EXCLRD). Since
other users will be locked out of the table, running with repeatable read
will prevent concurrent access of the table.</p>
</div>
<div class="section"><p>If an isolation level other then COMMIT(*NONE) was specified and
the application issues a ROLLBACK or the activation group ends abnormally
(and the commitment definition is not *JOB), all updates, inserts, deletes,
and DDL operations made within the unit of work are backed out. If the application
issues a COMMIT or the activation group ends normally, all updates, inserts,
deletes, and DDL operations made within the unit of work are committed.</p>
</div>
<div class="section"><p><span class="keyword">DB2 UDB for iSeries</span> uses locks
on rows to keep other jobs from accessing changed data before a unit of work
completes. If COMMIT(*ALL) is specified, read locks on rows fetched are also
used to prevent other jobs from changing data that was read before a unit
of work completes. This will not prevent other jobs from reading the unchanged
rows. This ensures that, if the same unit of work rereads a row, it gets the
same result. Read locks do not prevent other jobs from fetching the same rows.</p>
</div>
<div class="section"><p>Commitment control handles up to 500 million distinct row changes
in a unit of work. If COMMIT(*ALL) or COMMIT(*RR) is specified, all rows read
are also included in the limit. (If a row is changed or read more than once
in a unit of work, it is only counted once toward the limit.) Holding a large
number of locks adversely affects system performance and does not allow concurrent
users to access rows locked in the unit of work until the end of the unit
of work. It is in your best interest to keep the number of rows processed
in a unit of work small.</p>
</div>
<div class="section"><p>Commitment control will allow up to 512 files for each journal
to be open under commitment control or closed with pending changes in a unit
of work.</p>
</div>
<div class="section"><p>COMMIT HOLD and ROLLBACK HOLD allows you to keep the cursor open
and start another unit of work without issuing an OPEN again. The HOLD value
is not available when you are connected to a remote database that is not on
an <span class="keyword">iSeries</span> system. However,
the WITH HOLD option on DECLARE CURSOR may be used to keep the cursor open
after a COMMIT. This type of cursor is supported when you are connected to
a remote database that is not on an <span class="keyword">iSeries</span> system.
Such a cursor is closed on a rollback.</p>
</div>
<div class="tablenoborder"><a name="rbafydicomm__reclock"><!-- --></a><table cellpadding="4" cellspacing="0" summary="" id="rbafydicomm__reclock" width="100%" frame="border" border="1" rules="all"><caption>Table 1. Row lock duration</caption><thead align="left"><tr><th align="left" valign="bottom" width="20.754716981132077%" id="d0e194">SQL statement</th>
<th align="left" valign="bottom" width="22.641509433962266%" id="d0e196">COMMIT parameter (see note 5)</th>
<th align="left" valign="bottom" width="45.28301886792453%" id="d0e198">Duration of row locks</th>
<th align="left" valign="bottom" width="11.320754716981133%" id="d0e200">Lock type</th>
</tr>
</thead>
<tbody><tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 "> <p>SELECT INTO<br />
SET variable<br />
VALUES INTO</p>
</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS (See note 6)<br />
*ALL (See note 2 and 7)</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>No locks<br />
No locks<br />
Row locked when read and released<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p> <br />
 <br />
READ<br />
READ</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">FETCH (read-only cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS (See note 6)<br />
*ALL (See note 2 and 7)</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>No locks<br />
No locks<br />
From read until the next FETCH<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p> <br />
 <br />
READ<br />
READ</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">FETCH (update or delete capable cursor) (See
note 1)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
 <br />
 <br />
 <br />
*CHG<br />
 <br />
 <br />
 <br />
*CS<br />
 <br />
 <br />
 <br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>When row not updated or deleted<br />
from read until next FETCH<br />
When row is updated or deleted<br />
from read until UPDATE or DELETE<br />
When row not updated or deleted<br />
from read until next FETCH<br />
When row is updated or deleted<br />
from read until COMMIT or ROLLBACK<br />
When row not updated or deleted<br />
from read until next FETCH<br />
When row is updated or deleted<br />
from read until COMMIT or ROLLBACK<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>UPDATE<br />
 <br />
 <br />
 <br />
UPDATE<br />
 <br />
 <br />
 <br />
UPDATE<br />
 <br />
 <br />
 <br />
UPDATE</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">INSERT (target table)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>No locks<br />
From insert until ROLLBACK or COMMIT<br />
From insert until ROLLBACK or COMMIT<br />
From insert until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p> <br />
UPDATE<br />
UPDATE<br />
UPDATE<sup>3</sup></p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">INSERT (tables in subselect)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>No locks<br />
No locks<br />
Each row locked while being read<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p> <br />
 <br />
READ<br />
READ</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">UPDATE (non-cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>Each row locked while being updated<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>UPDATE<br />
UPDATE<br />
UPDATE<br />
UPDATE</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">DELETE (non-cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>Each row locked while being deleted<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>UPDATE<br />
UPDATE<br />
UPDATE<br />
UPDATE</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">UPDATE (with cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>Lock released when row updated<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>UPDATE<br />
UPDATE<br />
UPDATE<br />
UPDATE</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">DELETE (with cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>Lock released when row deleted<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>UPDATE<br />
UPDATE<br />
UPDATE<br />
UPDATE</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">Subqueries (update or delete capable cursor
or UPDATE or DELETE non-cursor)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL (see note 2)</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>From read until next FETCH<br />
From read until next FETCH<br />
From read until next FETCH<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p>READ<br />
READ<br />
READ<br />
READ</p>
</td>
</tr>
<tr><td align="left" valign="top" width="20.754716981132077%" headers="d0e194 ">Subqueries (read-only cursor or SELECT INTO)</td>
<td align="left" valign="top" width="22.641509433962266%" headers="d0e196 "> <p>*NONE<br />
*CHG<br />
*CS<br />
*ALL</p>
</td>
<td align="left" valign="top" width="45.28301886792453%" headers="d0e198 "> <p>No locks<br />
No locks<br />
Each row locked while being read<br />
From read until ROLLBACK or COMMIT</p>
</td>
<td align="left" valign="top" width="11.320754716981133%" headers="d0e200 "> <p> <br />
 <br />
READ<br />
READ</p>
</td>
</tr>
<tr><td colspan="4" align="left" valign="top" headers="d0e194 d0e196 d0e198 d0e200 "><div class="note"><span class="notetitle">Notes:</span> <ol><li>A cursor is open with UPDATE or DELETE capabilities if the result table
is not read-only and if one of the following is true: <ul><li>The cursor is defined with a FOR UPDATE clause.</li>
<li>The cursor is defined without a FOR UPDATE, FOR READ ONLY, or ORDER BY
clause and the program contains at least one of the following: <ul><li>Cursor UPDATE referring to the same cursor-name</li>
<li>Cursor DELETE referring to the same cursor-name</li>
<li>An EXECUTE or EXECUTE IMMEDIATE statement and ALWBLK(*READ) or ALWBLK(*NONE)
was specified on the CRTSQLxxx command.</li>
</ul>
</li>
</ul>
</li>
<li>A table or view can be locked exclusively in order to satisfy COMMIT(*ALL).
If a subselect is processed that includes a UNION, or if the processing of
the query requires the use of a temporary result, an exclusive lock is acquired
to protect you from seeing uncommitted changes.</li>
<li>An UPDATE lock on rows of the target table and a READ lock on the rows
of the subselect table.</li>
<li>A table or view can be locked exclusively in order to satisfy repeatable
read. Row locking is still done under repeatable read. The locks acquired
and their duration are identical to *ALL.</li>
<li>Repeatable read (*RR) row locks will be the same as the locks indicated
for *ALL.</li>
<li>If the KEEP LOCKS clause is specified with *CS, any read locks are held
until the cursor is closed or until a COMMIT or ROLLBACK is done. If no cursors
are associated with the isolation clause, then locks are held until the completion
of the SQL statement.</li>
<li>If the USE AND KEEP EXCLUSIVE LOCKS clause is specified with the *RS or
*RR isolation level, an UPDATE lock on the row will be obtained instead of
a READ lock.</li>
</ol>
</div>
</td>
</tr>
</tbody>
</table>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafydataintex.htm" title="Data integrity protects data from being destroyed or changed by unauthorized persons, system operation or hardware failures (such as physical damage to a disk), programming errors, interruptions before a job is completed (such as a power failure), or interference from running applications at the same time (such as serialization problems).">Data integrity</a></div>
</div>
<div class="relinfo"><strong>Related information</strong><br />
<div><a href="../db2/rbafzmsth2clcu.htm">DECLARE CURSOR statement</a></div>
<div><a href="../db2/rbafzmstisol.htm">Isolation Level</a></div>
<div><a href="../rzakj/rzakjcommitkickoff.htm">Commitment control</a></div>
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