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Rename PGPROC fields related to group XID clearing again.

Browse Source 
Commit 0e141c0fbb introduced a new
facility to reduce ProcArrayLock contention by clearing several XIDs
from the ProcArray under a single lock acquisition.  The names
initially chosen were deemed not to be very good choices, so commit
4aec49899e renamed them.  But now it
seems like we still didn't get it right.  A pending patch wants to
add similar infrastructure for batching CLOG updates, so the names
need to be clear enough to allow a new set of structure members with
a related purpose.

Amit Kapila
This commit is contained in:
Robert Haas
2016-02-11 08:55:24 -05:00
parent 4c9864b9b4
commit a455878d99
3 changed files with 28 additions and 22 deletions
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28
src/backend/storage/ipc/procarray.c
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@@ -497,14 +497,14 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
Assert(TransactionIdIsValid(allPgXact[proc->pgprocno].xid));
/* Add ourselves to the list of processes needing a group XID clear. */
proc->clearXid = true;
proc->backendLatestXid = latestXid;
proc->procArrayGroupMember = true;
proc->procArrayGroupMemberXid = latestXid;
while (true)
{
nextidx = pg_atomic_read_u32(&procglobal->firstClearXidElem);
pg_atomic_write_u32(&proc->nextClearXidElem, nextidx);
nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
pg_atomic_write_u32(&proc->procArrayGroupNext, nextidx);
if (pg_atomic_compare_exchange_u32(&procglobal->firstClearXidElem,
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
&nextidx,
(uint32) proc->pgprocno))
break;
@@ -523,12 +523,12 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
{
/* acts as a read barrier */
PGSemaphoreLock(&proc->sem);
if (!proc->clearXid)
if (!proc->procArrayGroupMember)
break;
extraWaits++;
}
Assert(pg_atomic_read_u32(&proc->nextClearXidElem) == INVALID_PGPROCNO);
Assert(pg_atomic_read_u32(&proc->procArrayGroupNext) == INVALID_PGPROCNO);
/* Fix semaphore count for any absorbed wakeups */
while (extraWaits-- > 0)
@@ -546,8 +546,8 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
*/
while (true)
{
nextidx = pg_atomic_read_u32(&procglobal->firstClearXidElem);
if (pg_atomic_compare_exchange_u32(&procglobal->firstClearXidElem,
nextidx = pg_atomic_read_u32(&procglobal->procArrayGroupFirst);
if (pg_atomic_compare_exchange_u32(&procglobal->procArrayGroupFirst,
&nextidx,
INVALID_PGPROCNO))
break;
@@ -562,10 +562,10 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
PGPROC *proc = &allProcs[nextidx];
PGXACT *pgxact = &allPgXact[nextidx];
ProcArrayEndTransactionInternal(proc, pgxact, proc->backendLatestXid);
ProcArrayEndTransactionInternal(proc, pgxact, proc->procArrayGroupMemberXid);
/* Move to next proc in list. */
nextidx = pg_atomic_read_u32(&proc->nextClearXidElem);
nextidx = pg_atomic_read_u32(&proc->procArrayGroupNext);
}
/* We're done with the lock now. */
@@ -582,13 +582,13 @@ ProcArrayGroupClearXid(PGPROC *proc, TransactionId latestXid)
{
PGPROC *proc = &allProcs[wakeidx];
wakeidx = pg_atomic_read_u32(&proc->nextClearXidElem);
pg_atomic_write_u32(&proc->nextClearXidElem, INVALID_PGPROCNO);
wakeidx = pg_atomic_read_u32(&proc->procArrayGroupNext);
pg_atomic_write_u32(&proc->procArrayGroupNext, INVALID_PGPROCNO);
/* ensure all previous writes are visible before follower continues. */
pg_write_barrier();
proc->clearXid = false;
proc->procArrayGroupMember = false;
if (proc != MyProc)
PGSemaphoreUnlock(&proc->sem);