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Commitfcd8d25

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amcheck: editorialize variable name & comment.
No exclusive lock is taken anymore...
1 parent56018bf commitfcd8d25

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+38
-39
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1 file changed

+38
-39
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‎contrib/amcheck/verify_nbtree.c

Lines changed: 38 additions & 39 deletions
Original file line numberDiff line numberDiff line change
@@ -55,8 +55,8 @@ typedef struct BtreeCheckState
5555

5656
/* B-Tree Index Relation */
5757
Relationrel;
58-
/*ExclusiveLock held? */
59-
boolexclusivelylocked;
58+
/*ShareLock held on heap/index, rather than AccessShareLock? */
59+
boolreadonly;
6060
/* Per-page context */
6161
MemoryContexttargetcontext;
6262
/* Buffer access strategy */
@@ -94,7 +94,7 @@ PG_FUNCTION_INFO_V1(bt_index_parent_check);
9494

9595
staticvoidbt_index_check_internal(Oidindrelid,boolparentcheck);
9696
staticinlinevoidbtree_index_checkable(Relationrel);
97-
staticvoidbt_check_every_level(Relationrel,boolexclusivelylocked);
97+
staticvoidbt_check_every_level(Relationrel,boolreadonly);
9898
staticBtreeLevelbt_check_level_from_leftmost(BtreeCheckState*state,
9999
BtreeLevellevel);
100100
staticvoidbt_target_page_check(BtreeCheckState*state);
@@ -256,23 +256,23 @@ btree_index_checkable(Relation rel)
256256
* logical order, verifying invariants as it goes.
257257
*
258258
* It is the caller's responsibility to acquire appropriate heavyweight lock on
259-
* the index relation, and advise us if extra checks are safe whenan
260-
*ExclusiveLockis held.
259+
* the index relation, and advise us if extra checks are safe whena ShareLock
260+
* is held.
261261
*
262-
*An ExclusiveLock is generally assumed to prevent any kind of physical
262+
*A ShareLock is generally assumed to prevent any kind of physical
263263
* modification to the index structure, including modifications that VACUUM may
264264
* make. This does not include setting of the LP_DEAD bit by concurrent index
265265
* scans, although that is just metadata that is not able to directly affect
266266
* any check performed here. Any concurrent process that might act on the
267267
* LP_DEAD bit being set (recycle space) requires a heavyweight lock that
268-
* cannot be held while we holdan ExclusiveLock. (Besides, even if that could
268+
* cannot be held while we holda ShareLock. (Besides, even if that could
269269
* happen, the ad-hoc recycling when a page might otherwise split is performed
270270
* per-page, and requires an exclusive buffer lock, which wouldn't cause us
271271
* trouble. _bt_delitems_vacuum() may only delete leaf items, and so the extra
272272
* parent/child check cannot be affected.)
273273
*/
274274
staticvoid
275-
bt_check_every_level(Relationrel,boolexclusivelylocked)
275+
bt_check_every_level(Relationrel,boolreadonly)
276276
{
277277
BtreeCheckState*state;
278278
Pagemetapage;
@@ -291,7 +291,7 @@ bt_check_every_level(Relation rel, bool exclusivelylocked)
291291
*/
292292
state=palloc(sizeof(BtreeCheckState));
293293
state->rel=rel;
294-
state->exclusivelylocked=exclusivelylocked;
294+
state->readonly=readonly;
295295
/* Create context for page */
296296
state->targetcontext=AllocSetContextCreate(CurrentMemoryContext,
297297
"amcheck context",
@@ -353,7 +353,7 @@ bt_check_every_level(Relation rel, bool exclusivelylocked)
353353

354354
/*
355355
* Given a left-most block at some level, move right, verifying each page
356-
* individually (with more verification across pages for "exclusivelylocked"
356+
* individually (with more verification across pages for "readonly"
357357
* callers). Caller should pass the true root page as the leftmost initially,
358358
* working their way down by passing what is returned for the last call here
359359
* until level 0 (leaf page level) was reached.
@@ -428,7 +428,7 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
428428
* locking, check that the first valid page meets caller's
429429
* expectations.
430430
*/
431-
if (state->exclusivelylocked)
431+
if (state->readonly)
432432
{
433433
if (!P_LEFTMOST(opaque))
434434
ereport(ERROR,
@@ -482,7 +482,7 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
482482
*/
483483
}
484484

485-
if (state->exclusivelylocked&&opaque->btpo_prev!=leftcurrent)
485+
if (state->readonly&&opaque->btpo_prev!=leftcurrent)
486486
ereport(ERROR,
487487
(errcode(ERRCODE_INDEX_CORRUPTED),
488488
errmsg("left link/right link pair in index \"%s\" not in agreement",
@@ -541,7 +541,7 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
541541
* "real" data item on the page to the right (if such a first item is
542542
* available).
543543
*
544-
* Furthermore, when state passed showsExclusiveLock held, and target page is
544+
* Furthermore, when state passed showsShareLock held, and target page is
545545
* internal page, function also checks:
546546
*
547547
* - That all child pages respect downlinks lower bound.
@@ -597,8 +597,8 @@ bt_target_page_check(BtreeCheckState *state)
597597
* page items.
598598
*
599599
* We prefer to check all items against high key rather than checking
600-
* just thefirst and trusting that the operator class obeys the
601-
* transitive law (which implies that allsubsequent items also
600+
* just thelast and trusting that the operator class obeys the
601+
* transitive law (which implies that allprevious items also
602602
* respected the high key invariant if they pass the item order
603603
* check).
604604
*
@@ -705,21 +705,20 @@ bt_target_page_check(BtreeCheckState *state)
705705
{
706706
/*
707707
* As explained at length in bt_right_page_check_scankey(),
708-
* there is a known !exclusivelylocked race that could account
709-
*forapparent violation of invariant, which we must check
710-
*forbefore actually proceeding with raising error. Our
711-
*canarycondition is that target page was deleted.
708+
* there is a known !readonly race that could account for
709+
* apparent violation of invariant, which we must check for
710+
* before actually proceeding with raising error. Our canary
711+
* condition is that target page was deleted.
712712
*/
713-
if (!state->exclusivelylocked)
713+
if (!state->readonly)
714714
{
715715
/* Get fresh copy of target page */
716716
state->target=palloc_btree_page(state,state->targetblock);
717717
/* Note that we deliberately do not update target LSN */
718718
topaque= (BTPageOpaque)PageGetSpecialPointer(state->target);
719719

720720
/*
721-
* All !exclusivelylocked checks now performed; just
722-
* return
721+
* All !readonly checks now performed; just return
723722
*/
724723
if (P_IGNORE(topaque))
725724
return;
@@ -740,11 +739,11 @@ bt_target_page_check(BtreeCheckState *state)
740739
* * Downlink check *
741740
*
742741
* Additional check of child items iff this is an internal page and
743-
* caller holdsan ExclusiveLock. This happens for every downlink
744-
*(item)in target excluding the negative-infinity downlink (again,
745-
*this isbecause it has no useful value to compare).
742+
* caller holdsa ShareLock. This happens for every downlink (item)
743+
* in target excluding the negative-infinity downlink (again, this is
744+
* because it has no useful value to compare).
746745
*/
747-
if (!P_ISLEAF(topaque)&&state->exclusivelylocked)
746+
if (!P_ISLEAF(topaque)&&state->readonly)
748747
{
749748
BlockNumberchildblock=ItemPointerGetBlockNumber(&(itup->t_tid));
750749

@@ -766,7 +765,7 @@ bt_target_page_check(BtreeCheckState *state)
766765
* with different parent page). If no such valid item is available, return
767766
* NULL instead.
768767
*
769-
* Note that !exclusivelylocked callers must reverify that target page has not
768+
* Note that !readonly callers must reverify that target page has not
770769
* been concurrently deleted.
771770
*/
772771
staticScanKey
@@ -833,14 +832,14 @@ bt_right_page_check_scankey(BtreeCheckState *state)
833832
}
834833

835834
/*
836-
* NoExclusiveLock held case -- why it's safe to proceed.
835+
* NoShareLock held case -- why it's safe to proceed.
837836
*
838837
* Problem:
839838
*
840839
* We must avoid false positive reports of corruption when caller treats
841840
* item returned here as an upper bound on target's last item. In
842841
* general, false positives are disallowed. Avoiding them here when
843-
* caller is !exclusivelylocked is subtle.
842+
* caller is !readonly is subtle.
844843
*
845844
* A concurrent page deletion by VACUUM of the target page can result in
846845
* the insertion of items on to this right sibling page that would
@@ -892,7 +891,7 @@ bt_right_page_check_scankey(BtreeCheckState *state)
892891
*
893892
* Top level tree walk caller moves on to next page (makes it the new
894893
* target) following recovery from this race. (cf. The rationale for
895-
* child/downlink verification needingan ExclusiveLock within
894+
* child/downlink verification needinga ShareLock within
896895
* bt_downlink_check(), where page deletion is also the main source of
897896
* trouble.)
898897
*
@@ -984,7 +983,7 @@ bt_downlink_check(BtreeCheckState *state, BlockNumber childblock,
984983
BTPageOpaquecopaque;
985984

986985
/*
987-
* Caller must haveExclusiveLock on target relation, because of
986+
* Caller must haveShareLock on target relation, because of
988987
* considerations around page deletion by VACUUM.
989988
*
990989
* NB: In general, page deletion deletes the right sibling's downlink, not
@@ -994,8 +993,8 @@ bt_downlink_check(BtreeCheckState *state, BlockNumber childblock,
994993
* page's rightmost child unless it is the last child page, and we intend
995994
* to also delete the parent itself.)
996995
*
997-
* If this verification happened withoutan ExclusiveLock, the following
998-
*racecondition could cause false positives:
996+
* If this verification happened withouta ShareLock, the following race
997+
* condition could cause false positives:
999998
*
1000999
* In general, concurrent page deletion might occur, including deletion of
10011000
* the left sibling of the child page that is examined here. If such a
@@ -1009,19 +1008,19 @@ bt_downlink_check(BtreeCheckState *state, BlockNumber childblock,
10091008
* part of deletion's first phase.)
10101009
*
10111010
* Note that while the cross-page-same-level last item check uses a trick
1012-
* that allows it to perform verification for !exclusivelylocked callers,
1013-
*a similartrick seems difficult here. The trick that that other check
1014-
*uses is,in essence, to lock down race conditions to those that occur
1015-
*due toconcurrent page deletion of the target; that's a race that can
1016-
*bereliably detected before actually reporting corruption.
1011+
* that allows it to perform verification for !readonly callers, a similar
1012+
* trick seems difficult here. The trick that that other check uses is,
1013+
* in essence, to lock down race conditions to those that occur due to
1014+
* concurrent page deletion of the target; that's a race that can be
1015+
* reliably detected before actually reporting corruption.
10171016
*
10181017
* On the other hand, we'd need to lock down race conditions involving
10191018
* deletion of child's left page, for long enough to read the child page
10201019
* into memory (in other words, a scheme with concurrently held buffer
10211020
* locks on both child and left-of-child pages). That's unacceptable for
10221021
* amcheck functions on general principle, though.
10231022
*/
1024-
Assert(state->exclusivelylocked);
1023+
Assert(state->readonly);
10251024

10261025
/*
10271026
* Verify child page has the downlink key from target page (its parent) as

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