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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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8
src/include/storage/buf_internals.h
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@@ -18,6 +18,7 @@
#include "port/atomics.h"
#include "storage/buf.h"
#include "storage/bufmgr.h"
#include "storage/condition_variable.h"
#include "storage/latch.h"
#include "storage/lwlock.h"
#include "storage/shmem.h"
@@ -184,7 +185,6 @@ typedef struct BufferDesc
int wait_backend_pid; /* backend PID of pin-count waiter */
int freeNext; /* link in freelist chain */
LWLock content_lock; /* to lock access to buffer contents */
} BufferDesc;
@@ -221,12 +221,12 @@ typedef union BufferDescPadded
#define BufferDescriptorGetBuffer(bdesc) ((bdesc)->buf_id + 1)
#define BufferDescriptorGetIOLock(bdesc) \
(&(BufferIOLWLockArray[(bdesc)->buf_id]).lock)
#define BufferDescriptorGetIOCV(bdesc) \
(&(BufferIOCVArray[(bdesc)->buf_id]).cv)
#define BufferDescriptorGetContentLock(bdesc) \
((LWLock*) (&(bdesc)->content_lock))
extern PGDLLIMPORT LWLockMinimallyPadded *BufferIOLWLockArray;
extern PGDLLIMPORT ConditionVariableMinimallyPadded *BufferIOCVArray;
/*
* The freeNext field is either the index of the next freelist entry,