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Commit15ef6ff

Browse files
author
Amit Kapila
committed
Assert that we don't acquire a heavyweight lock on another object after
relation extension lock.The only exception to the rule is that we can try to acquire the samerelation extension lock more than once. This is allowed as we are notcreating any new lock for this case. This restriction implies that therelation extension lock won't ever participate in the deadlock cyclebecause we can never wait for any other heavyweight lock after acquiringthis lock.Such a restriction is okay for relation extension locks as unlike otherheavyweight locks these are not held till the transaction end. These aretaken for a short duration to extend a particular relation and thenreleased.Author: Dilip Kumar, with few changes by Amit KapilaReviewed-by: Amit Kapila, Kuntal Ghosh and Sawada MasahikoDiscussion:https://postgr.es/m/CAD21AoCmT3cFQUN4aVvzy5chw7DuzXrJCbrjTU05B+Ss=Gn1LA@mail.gmail.com
1 parentb897b3a commit15ef6ff

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2 files changed

+48
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‎src/backend/storage/lmgr/lock.c

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Original file line numberDiff line numberDiff line change
@@ -170,6 +170,21 @@ typedef struct TwoPhaseLockRecord
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*/
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staticintFastPathLocalUseCount=0;
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/*
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* Flag to indicate if the relation extension lock is held by this backend.
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* This flag is used to ensure that while holding the relation extension lock
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* we don't try to acquire a heavyweight lock on any other object. This
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* restriction implies that the relation extension lock won't ever participate
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* in the deadlock cycle because we can never wait for any other heavyweight
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* lock after acquiring this lock.
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*
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* Such a restriction is okay for relation extension locks as unlike other
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* heavyweight locks these are not held till the transaction end. These are
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* taken for a short duration to extend a particular relation and then
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* released.
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*/
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staticboolIsRelationExtensionLockHeldPG_USED_FOR_ASSERTS_ONLY= false;
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/* Macros for manipulating proc->fpLockBits */
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#defineFAST_PATH_BITS_PER_SLOT3
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#defineFAST_PATH_LOCKNUMBER_OFFSET1
@@ -840,6 +855,13 @@ LockAcquireExtended(const LOCKTAG *locktag,
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returnLOCKACQUIRE_ALREADY_HELD;
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}
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/*
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* We don't acquire any other heavyweight lock while holding the relation
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* extension lock. We do allow to acquire the same relation extension
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* lock more than once but that case won't reach here.
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*/
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Assert(!IsRelationExtensionLockHeld);
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/*
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* Prepare to emit a WAL record if acquisition of this lock needs to be
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* replayed in a standby server.
@@ -1287,6 +1309,23 @@ SetupLockInTable(LockMethod lockMethodTable, PGPROC *proc,
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returnproclock;
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}
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/*
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* Check and set/reset the flag that we hold the relation extension lock.
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*
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* It is callers responsibility that this function is called after
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* acquiring/releasing the relation extension lock.
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*
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* Pass acquired as true if lock is acquired, false otherwise.
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*/
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staticinlinevoid
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CheckAndSetLockHeld(LOCALLOCK*locallock,boolacquired)
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{
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#ifdefUSE_ASSERT_CHECKING
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if (LOCALLOCK_LOCKTAG(*locallock)==LOCKTAG_RELATION_EXTEND)
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IsRelationExtensionLockHeld=acquired;
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#endif
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}
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/*
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* Subroutine to free a locallock entry
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*/
@@ -1322,6 +1361,11 @@ RemoveLocalLock(LOCALLOCK *locallock)
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(void*)&(locallock->tag),
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HASH_REMOVE,NULL))
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elog(WARNING,"locallock table corrupted");
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/*
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* Indicate that the lock is released for certain types of locks
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*/
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CheckAndSetLockHeld(locallock, false);
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}
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/*
@@ -1618,6 +1662,9 @@ GrantLockLocal(LOCALLOCK *locallock, ResourceOwner owner)
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locallock->numLockOwners++;
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if (owner!=NULL)
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ResourceOwnerRememberLock(owner,locallock);
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/* Indicate that the lock is acquired for certain types of locks. */
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CheckAndSetLockHeld(locallock, true);
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}
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/*

‎src/include/storage/lock.h

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Original file line numberDiff line numberDiff line change
@@ -419,6 +419,7 @@ typedef struct LOCALLOCK
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}LOCALLOCK;
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#defineLOCALLOCK_LOCKMETHOD(llock) ((llock).tag.lock.locktag_lockmethodid)
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#defineLOCALLOCK_LOCKTAG(llock) ((LockTagType) (llock).tag.lock.locktag_type)
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/*

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