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Commit0fad355

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Update obsolete comments in lwlock.h.
The typical size of an LWLock is now 16 bytes even on 64-bit platforms,and the size of slock_t is now irrelevant. But pg_atomic_uint32 can(perhaps surprisingly) still be larger than 4 bytes, so there's stillsome marginal point to allowing LWLOCK_MINIMAL_SIZE == 64.Commit008608b made the changesthat led to the need for these updates.
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‎src/include/storage/lwlock.h

Lines changed: 9 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -58,16 +58,17 @@ typedef struct LWLock
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* LWLockPadded can be used for cases where we want each lock to be an entire
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* cache line.
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*
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*On 32-bit platforms, anLWLockMinimallyPadded mightactuallycontain more
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*than the absolute minimum amountof padding required to keep a lock from
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*crossing a cache line boundary,because an unpadded LWLockmightfit into
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*16 bytes. We ignore thatpossibility when determining the minimal amount
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*of padding. Older releaseshad larger LWLocks, so 32 really was the
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*minimum, and packing them intighter might hurt performance.
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*AnLWLockMinimallyPadded might contain more than the absolute minimum amount
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* of padding required to keep a lock from crossing a cache line boundary,
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* because an unpadded LWLockwill normallyfit into 16 bytes. We ignore that
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* possibility when determining the minimal amount of padding. Older releases
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* had larger LWLocks, so 32 really was the minimum, and packing them in
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* tighter might hurt performance.
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*
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* LWLOCK_MINIMAL_SIZE should be 32 on basically all common platforms, but
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* because slock_t is more than 2 bytes on some obscure platforms, we allow
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* for the possibility that it might be 64.
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* because pg_atomic_uint32 is more than 4 bytes on some obscure platforms, we
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* allow for the possibility that it might be 64. Even on those platforms,
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* we probably won't exceed 32 bytes unless LOCK_DEBUG is defined.
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*/
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#defineLWLOCK_PADDED_SIZEPG_CACHE_LINE_SIZE
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#defineLWLOCK_MINIMAL_SIZE (sizeof(LWLock) <= 32 ? 32 : 64)

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