/*
* This must be called ONCE during postmaster or standalone-backend startup,
* after StartupXLOG has initialized ShmemVariableCache->nextXid.
*
* oldestActiveXID is the oldest XID of any prepared transaction, or nextXid
* if there are none.
*/
void
StartupSUBTRANS(TransactionId oldestActiveXID)
{
int startPage;
int endPage;
/*
* Since we don't expect pg_subtrans to be valid across crashes, we
* initialize the currently-active page(s) to zeroes during startup.
* Whenever we advance into a new page, ExtendSUBTRANS will likewise zero
* the new page without regard to whatever was previously on disk.
*/
LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
startPage = TransactionIdToPage(oldestActiveXID);
endPage = TransactionIdToPage(ShmemVariableCache->nextXid);
while (startPage != endPage)
{
(void) ZeroSUBTRANSPage(startPage);
startPage++;
}
(void) ZeroSUBTRANSPage(startPage);
LWLockRelease(SubtransControlLock);
}
/*
* Make sure that SUBTRANS has room for a newly-allocated XID.
*
* NB: this is called while holding XidGenLock. We want it to be very fast
* most of the time; even when it's not so fast, no actual I/O need happen
* unless we're forced to write out a dirty subtrans page to make room
* in shared memory.
*/
void
ExtendSUBTRANS(TransactionId newestXact)
{
int pageno;
/*
* Caller must have already taken mirrored lock shared.
*/
/*
* No work except at first XID of a page. But beware: just after
* wraparound, the first XID of page zero is FirstNormalTransactionId.
*/
if (TransactionIdToEntry(newestXact) != 0 &&
!TransactionIdEquals(newestXact, FirstNormalTransactionId))
return;
pageno = TransactionIdToPage(newestXact);
LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
/* Zero the page */
ZeroSUBTRANSPage(pageno);
LWLockRelease(SubtransControlLock);
}
/*
* Make sure that SUBTRANS has room for a newly-allocated XID.
*
* NB: this is called while holding XidGenLock. We want it to be very fast
* most of the time; even when it's not so fast, no actual I/O need happen
* unless we're forced to write out a dirty subtrans page to make room
* in shared memory.
*/
void
ExtendSUBTRANS(TransactionId newestXact)
{
int pageno;
/*
* No work except at first XID of a page. But beware: just after
* wraparound, the first XID of page zero is FirstNormalTransactionId.
*/
#ifdef PGXC /* PGXC_COORD || PGXC_DATANODE */
/*
* In PGXC, it may be that a node is not involved in a transaction,
* and therefore will be skipped, so we need to detect this by using
* the latest_page_number instead of the pg index.
*
* Also, there is a special case of when transactions wrap-around that
* we need to detect.
*/
pageno = TransactionIdToPage(newestXact);
/*
* The first condition makes sure we did not wrap around
* The second checks if we are still using the same page.
* Note that this value can change and we are not holding a lock,
* so we repeat the check below. We do it this way instead of
* grabbing the lock to avoid lock contention.
*/
if (SubTransCtl->shared->latest_page_number - pageno <= SUBTRANS_WRAP_CHECK_DELTA
&& pageno <= SubTransCtl->shared->latest_page_number)
return;
#else
if (TransactionIdToEntry(newestXact) != 0 &&
!TransactionIdEquals(newestXact, FirstNormalTransactionId))
return;
pageno = TransactionIdToPage(newestXact);
#endif
LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
#ifdef PGXC
/*
* We repeat the check. Another process may have written
* out the page already and advanced the latest_page_number
* while we were waiting for the lock.
*/
if (SubTransCtl->shared->latest_page_number - pageno <= SUBTRANS_WRAP_CHECK_DELTA
&& pageno <= SubTransCtl->shared->latest_page_number)
{
LWLockRelease(SubtransControlLock);
return;
}
#endif
/* Zero the page */
ZeroSUBTRANSPage(pageno);
LWLockRelease(SubtransControlLock);
}
/*
* This func must be called ONCE on system install. It creates
* the initial SUBTRANS segment. (The SUBTRANS directory is assumed to
* have been created by the initdb shell script, and SUBTRANSShmemInit
* must have been called already.)
*
* Note: it's not really necessary to create the initial segment now,
* since slru.c would create it on first write anyway. But we may as well
* do it to be sure the directory is set up correctly.
*/
void
BootStrapSUBTRANS(void)
{
int slotno;
LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
/* Create and zero the first page of the subtrans log */
slotno = ZeroSUBTRANSPage(0);
/* Make sure it's written out */
SimpleLruWritePage(SubTransCtl, slotno);
Assert(!SubTransCtl->shared->page_dirty[slotno]);
LWLockRelease(SubtransControlLock);
}
