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Commite68eb63

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Improve spelling of lock names, and some other editing.
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‎doc/src/sgml/mvcc.sgml‎

Lines changed: 82 additions & 80 deletions
Original file line numberDiff line numberDiff line change
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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/mvcc.sgml,v 2.23 2002/02/18 16:13:10 tgl Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/mvcc.sgml,v 2.24 2002/03/27 02:36:51 petere Exp $
33
-->
44

55
<chapter id="mvcc">
@@ -376,24 +376,28 @@ ERROR: Can't serialize access due to concurrent update
376376
</indexterm>
377377

378378
<para>
379-
<productname>PostgreSQL</productname>
380-
provides various lock modes tocontrol concurrent
381-
access to data in tables. Some of theselock modesare acquired by
382-
<productname>PostgreSQL</productname>
383-
automatically before statement execution, while others are
384-
provided to be used by applications. All lock modes acquired in a
385-
transaction are held for the duration
386-
ofthetransaction.
379+
<productname>PostgreSQL</productname> provides various lock modes
380+
to control concurrent access todata in tables. Users normally
381+
need not be concerned about the differentlock modesbecause
382+
<productname>PostgreSQL</productname> commands automatically
383+
acquire locks of appropriate modes to ensure data integrity while
384+
permitting an appropriate level of concurrent access.
385+
Nevertheless, a user can manually lock a table in any of the
386+
available modes usingthe<command>LOCK TABLE</command> command.
387387
</para>
388388

389-
<sect2>
390-
<title>Table-level locks</title>
389+
<para>
390+
The list below shows the available lock modes and the contexts in
391+
which they are used. Remember that all of these lock modes are
392+
table-level locks, even if the name contains the word
393+
<quote>row</quote>. The names of the lock modes are historical.
394+
</para>
391395

392-
<para>
393396
<variablelist>
397+
<title>Table-level lock modes</title>
394398
<varlistentry>
395399
<term>
396-
AccessShareLock
400+
<literal>ACCESS SHARE</literal>
397401
</term>
398402
<listitem>
399403
<para>
@@ -402,170 +406,169 @@ ERROR: Can't serialize access due to concurrent update
402406
</para>
403407

404408
<para>
405-
Conflicts with AccessExclusiveLock only.
409+
Conflicts with the <literal>ACCESS EXCLUSIVE</literal> lock
410+
mode only.
406411
</para>
407412
</listitem>
408413
</varlistentry>
409414

410415
<varlistentry>
411416
<term>
412-
RowShareLock
417+
<literal>ROW SHARE</literal>
413418
</term>
414419
<listitem>
415420
<para>
416-
Acquired by <command>SELECT FOR UPDATE</command>
417-
and <command>LOCK TABLE</command>
418-
<option>IN ROW SHARE MODE</option> statements.
421+
The <command>SELECT FOR UPDATE</command> command acquires a
422+
lock of this mode.
419423
</para>
420424

421425
<para>
422-
Conflicts with ExclusiveLock and AccessExclusiveLock modes.
426+
Conflicts with the <literal>EXCLUSIVE</literal> and
427+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
423428
</para>
424429
</listitem>
425430
</varlistentry>
426431

427432
<varlistentry>
428433
<term>
429-
RowExclusiveLock
434+
<literal>ROW EXCLUSIVE</literal>
430435
</term>
431436
<listitem>
432437
<para>
433-
Acquired by <command>UPDATE</command>, <command>DELETE</command>,
434-
<command>INSERT</command> and <command>LOCK TABLE</command>
435-
<option>IN ROW EXCLUSIVE MODE</option> statements.
438+
The commands <command>UPDATE</command>,
439+
<command>DELETE</command>, and <command>INSERT</command>
440+
automatically acquire this lock mode.
436441
</para>
437442

438443
<para>
439-
Conflicts with ShareLock, ShareRowExclusiveLock, ExclusiveLock and
440-
AccessExclusiveLock modes.
444+
Conflicts with the <literal>SHARE</literal>, <literal>SHARE ROW
445+
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
446+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
441447
</para>
442448
</listitem>
443449
</varlistentry>
444450

445451
<varlistentry>
446452
<term>
447-
ShareUpdateExclusiveLock
453+
<literal>SHARE UPDATE EXCLUSIVE</literal>
448454
</term>
449455
<listitem>
450456
<para>
451-
Acquired by <command>VACUUM</command> (without <option>FULL</option>)
452-
and <command>LOCK TABLE</command>
453-
<option>IN SHARE UPDATE EXCLUSIVE MODE</option>
454-
statements.
457+
Acquired by <command>VACUUM</command> (without <option>FULL</option>).
455458
</para>
456459

457460
<para>
458-
Conflicts with ShareUpdateExclusiveLock, ShareLock,
459-
ShareRowExclusiveLock, ExclusiveLock and AccessExclusiveLock modes.
461+
Conflicts with the <literal>SHARE UPDATE EXCLUSIVE</literal>,
462+
<literal>SHARE</literal>, <literal>SHARE ROW
463+
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
464+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
460465
</para>
461466
</listitem>
462467
</varlistentry>
463468

464469
<varlistentry>
465470
<term>
466-
ShareLock
471+
<literal>SHARE</literal>
467472
</term>
468473
<listitem>
469474
<para>
470-
Acquired by <command>CREATE INDEX</command>
471-
and <command>LOCK TABLE</command>
472-
<option>IN SHARE MODE</option>
473-
statements.
475+
Acquired by <command>CREATE INDEX</command>.
474476
</para>
475477

476478
<para>
477-
Conflicts with RowExclusiveLock, ShareUpdateExclusiveLock,
478-
ShareRowExclusiveLock,
479-
ExclusiveLock and AccessExclusiveLock modes.
479+
Conflicts with the <literal>ROW EXCLUSIVE</literal>,
480+
<literal>SHARE UPDATE EXCLUSIVE</literal>, <literal>SHARE ROW
481+
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
482+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
480483
</para>
481484
</listitem>
482485
</varlistentry>
483486

484487
<varlistentry>
485488
<term>
486-
ShareRowExclusiveLock
489+
<literal>SHARE ROW EXCLUSIVE</literal>
487490
</term>
488491
<listitem>
489492
<para>
490-
Acquired by <command>LOCK TABLE</command>
491-
<option>IN SHARE ROW EXCLUSIVE MODE</option> statements.
493+
This lock mode is not automatically acquired by any command.
492494
</para>
493495

494496
<para>
495-
Conflicts with RowExclusiveLock, ShareUpdateExclusiveLock,
496-
ShareLock, ShareRowExclusiveLock,
497-
ExclusiveLock and AccessExclusiveLock modes.
497+
Conflicts with the <literal>ROW EXCLUSIVE</literal>,
498+
<literal>SHARE UPDATE EXCLUSIVE</literal>,
499+
<literal>SHARE</literal>, <literal>SHARE ROW
500+
EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
501+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
498502
</para>
499503
</listitem>
500504
</varlistentry>
501505

502506
<varlistentry>
503507
<term>
504-
ExclusiveLock
508+
<literal>EXCLUSIVE LOCK</literal>
505509
</term>
506510
<listitem>
507511
<para>
508-
Acquired by <command>LOCK TABLE</command>
509-
<option>IN EXCLUSIVE MODE</option> statements.
512+
This lock mode is not automatically acquired by any command.
510513
</para>
511514

512515
<para>
513-
Conflicts with RowShareLock, RowExclusiveLock,
514-
ShareUpdateExclusiveLock, ShareLock,
515-
ShareRowExclusiveLock, ExclusiveLock and AccessExclusiveLock
516-
modes.
516+
Conflicts with the <literal>ROW SHARE</literal>, <literal>ROW
517+
EXCLUSIVE</literal>, <literal>SHARE UPDATE
518+
EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE
519+
ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
520+
<literal>ACCESS EXCLUSIVE</literal> lock modes.
517521
</para>
518522
</listitem>
519523
</varlistentry>
520524

521525
<varlistentry>
522526
<term>
523-
AccessExclusiveLock
527+
<literal>ACCESS EXCLUSIVE</literal>
524528
</term>
525529
<listitem>
526530
<para>
527-
Acquired by <command>ALTER TABLE</command>,
528-
<command>DROP TABLE</command>,
529-
<command>VACUUM FULL</command> and <command>LOCK TABLE</command>
530-
<option>IN ACCESS EXCLUSIVE MODE</option> (or plain
531-
<command>LOCK TABLE</command>) statements.
531+
Acquired by the <command>ALTER TABLE</command>, <command>DROP
532+
TABLE</command>, and <command>VACUUM FULL</command> commands.
533+
This is also the default lock mode for <command>LOCK TABLE</command>
534+
statements that do not specify a mode explicitly.
532535
</para>
533536

534537
<para>
535-
Conflicts with all modes (AccessShareLock, RowShareLock,
536-
RowExclusiveLock, ShareUpdateExclusiveLock, ShareLock,
537-
ShareRowExclusiveLock, ExclusiveLock and AccessExclusiveLock).
538+
Conflicts with locks of all modes ( <literal>ACCESS
539+
SHARE</literal>, <literal>ROW SHARE</literal>, <literal>ROW
540+
EXCLUSIVE</literal>, <literal>SHARE UPDATE
541+
EXCLUSIVE</literal>, <literal>SHARE</literal>, <literal>SHARE
542+
ROW EXCLUSIVE</literal>, <literal>EXCLUSIVE</literal>, and
543+
<literal>ACCESS EXCLUSIVE</literal>).
538544
</para>
539545
</listitem>
540546
</varlistentry>
541547
</variablelist>
542548

543549
<note>
544550
<para>
545-
Only AccessExclusiveLock blocks <command>SELECT</command> (without
546-
<option>FOR UPDATE</option>) statement.
551+
Only an <literal>ACCESS EXCLUSIVE</literal> lock blocks a
552+
<command>SELECT</command> (without <option>FOR UPDATE</option>)
553+
statement.
547554
</para>
548555
</note>
549-
</para>
550-
</sect2>
551-
552-
<sect2>
553-
<title>Row-level locks</title>
554556

555557
<para>
556-
Row-level locks are acquired when rows are being updated (or deleted or
557-
marked for update).
558-
Row-level locks don't affect data querying. They block
559-
writers to <emphasis>the same row</emphasis> only.
558+
In addition to table-level locks, there are row-level locks.
559+
Row-level locks are acquired when rows are being updated (or
560+
deleted or marked for update). Row-level locks don't affect data
561+
querying; they block writers to <emphasis>the same row</emphasis>
562+
only. Row-level locks cannot be acquired explicitly by the user.
560563
</para>
561564

562565
<para>
563-
<productname>PostgreSQL</productname>
564-
doesn't remember anyinformation about modified rows in memory and
565-
so has no limit tothe number of rows locked at one time. However,
566-
locking a rowmay cause a disk write; thus, for example,
567-
<command>SELECT FORUPDATE</command> will modify
568-
selected rows to mark them and sowill result in disk writes.
566+
<productname>PostgreSQL</productname> doesn't remember any
567+
information about modified rows in memory, so is has no limit to
568+
the number of rows locked at one time. However, locking a row
569+
may cause a disk write; thus, for example, <command>SELECT FOR
570+
UPDATE</command> will modify selected rows to mark them and so
571+
will result in disk writes.
569572
</para>
570573

571574
<para>
@@ -575,7 +578,6 @@ ERROR: Can't serialize access due to concurrent update
575578
updated. Application writers normally need not be concerned with
576579
page-level locks, but we mention them for completeness.
577580
</para>
578-
</sect2>
579581
</sect1>
580582

581583
<sect1 id="locking-indexes">

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