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Replace buffer I/O locks with condition variables.

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1.  Backends waiting for buffer I/O are now interruptible.

2.  If something goes wrong in a backend that is currently performing
I/O, waiting backends no longer wake up until that backend reaches
AbortBufferIO() and broadcasts on the CV.  Previously, any waiters would
wake up (because the I/O lock was automatically released) and then
busy-loop until AbortBufferIO() cleared BM_IO_IN_PROGRESS.

3.  LWLockMinimallyPadded is removed, as it would now be unused.

Author: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> (earlier version, 2016)
Discussion: https://postgr.es/m/CA%2BhUKGJ8nBFrjLuCTuqKN0pd2PQOwj9b_jnsiGFFMDvUxahj_A%40mail.gmail.com
Discussion: https://postgr.es/m/CA+Tgmoaj2aPti0yho7FeEf2qt-JgQPRWb0gci_o1Hfr=C56Xng@mail.gmail.com
This commit is contained in:
Thomas Munro
2021-03-11 10:05:58 +13:00
parent c3ffe34863
commit d87251048a
11 changed files with 61 additions and 116 deletions
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34
src/backend/storage/buffer/buf_init.c
View File

@@ -19,7 +19,7 @@
BufferDescPadded *BufferDescriptors;
char *BufferBlocks;
LWLockMinimallyPadded *BufferIOLWLockArray = NULL;
ConditionVariableMinimallyPadded *BufferIOCVArray;
WritebackContext BackendWritebackContext;
CkptSortItem *CkptBufferIds;
@@ -68,7 +68,7 @@ InitBufferPool(void)
{
bool foundBufs,
foundDescs,
foundIOLocks,
foundIOCV,
foundBufCkpt;
/* Align descriptors to a cacheline boundary. */
@@ -81,11 +81,11 @@ InitBufferPool(void)
ShmemInitStruct("Buffer Blocks",
NBuffers * (Size) BLCKSZ, &foundBufs);
/* Align lwlocks to cacheline boundary */
BufferIOLWLockArray = (LWLockMinimallyPadded *)
ShmemInitStruct("Buffer IO Locks",
NBuffers * (Size) sizeof(LWLockMinimallyPadded),
&foundIOLocks);
/* Align condition variables to cacheline boundary. */
BufferIOCVArray = (ConditionVariableMinimallyPadded *)
ShmemInitStruct("Buffer IO Condition Variables",
NBuffers * sizeof(ConditionVariableMinimallyPadded),
&foundIOCV);
/*
* The array used to sort to-be-checkpointed buffer ids is located in
@@ -98,10 +98,10 @@ InitBufferPool(void)
ShmemInitStruct("Checkpoint BufferIds",
NBuffers * sizeof(CkptSortItem), &foundBufCkpt);
if (foundDescs || foundBufs || foundIOLocks || foundBufCkpt)
if (foundDescs || foundBufs || foundIOCV || foundBufCkpt)
{
/* should find all of these, or none of them */
Assert(foundDescs && foundBufs && foundIOLocks && foundBufCkpt);
Assert(foundDescs && foundBufs && foundIOCV && foundBufCkpt);
/* note: this path is only taken in EXEC_BACKEND case */
}
else
@@ -131,8 +131,7 @@ InitBufferPool(void)
LWLockInitialize(BufferDescriptorGetContentLock(buf),
LWTRANCHE_BUFFER_CONTENT);
LWLockInitialize(BufferDescriptorGetIOLock(buf),
LWTRANCHE_BUFFER_IO);
ConditionVariableInit(BufferDescriptorGetIOCV(buf));
}
/* Correct last entry of linked list */
@@ -169,16 +168,9 @@ BufferShmemSize(void)
/* size of stuff controlled by freelist.c */
size = add_size(size, StrategyShmemSize());
/*
* It would be nice to include the I/O locks in the BufferDesc, but that
* would increase the size of a BufferDesc to more than one cache line,
* and benchmarking has shown that keeping every BufferDesc aligned on a
* cache line boundary is important for performance. So, instead, the
* array of I/O locks is allocated in a separate tranche. Because those
* locks are not highly contended, we lay out the array with minimal
* padding.
*/
size = add_size(size, mul_size(NBuffers, sizeof(LWLockMinimallyPadded)));
/* size of I/O condition variables */
size = add_size(size, mul_size(NBuffers,
sizeof(ConditionVariableMinimallyPadded)));
/* to allow aligning the above */
size = add_size(size, PG_CACHE_LINE_SIZE);