subtrans.h File Reference

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Functions
void	SubTransSetParent (TransactionId xid, TransactionId parent)
TransactionId	SubTransGetParent (TransactionId xid)
TransactionId	SubTransGetTopmostTransaction (TransactionId xid)
Size	SUBTRANSShmemSize (void)
void	SUBTRANSShmemInit (void)
void	BootStrapSUBTRANS (void)
void	StartupSUBTRANS (TransactionId oldestActiveXID)
void	CheckPointSUBTRANS (void)
void	ExtendSUBTRANS (TransactionId newestXact)
void	TruncateSUBTRANS (TransactionId oldestXact)

Function Documentation

BootStrapSUBTRANS()

void BootStrapSUBTRANS

(

void

)

Definition at line 269 of file subtrans.c.

{
    /* Zero the initial page and flush it to disk */
    SimpleLruZeroAndWritePage(SubTransCtl, 0);
}

References SimpleLruZeroAndWritePage(), and SubTransCtl.

Referenced by BootStrapXLOG().

CheckPointSUBTRANS()

void CheckPointSUBTRANS

(

void

)

Definition at line 329 of file subtrans.c.

{
    /*
     * Write dirty SUBTRANS pages to disk
     *
     * This is not actually necessary from a correctness point of view. We do
     * it merely to improve the odds that writing of dirty pages is done by
     * the checkpoint process and not by backends.
     */
    TRACE_POSTGRESQL_SUBTRANS_CHECKPOINT_START(true);
    SimpleLruWriteAll(SubTransCtl, true);
    TRACE_POSTGRESQL_SUBTRANS_CHECKPOINT_DONE(true);
}

References SimpleLruWriteAll(), and SubTransCtl.

Referenced by CheckPointGuts().

ExtendSUBTRANS()

void ExtendSUBTRANS

(

TransactionId

newestXact

)

Definition at line 353 of file subtrans.c.

{
    int64       pageno;
    LWLock     *lock;
 
    /*
     * 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);
 
    lock = SimpleLruGetBankLock(SubTransCtl, pageno);
    LWLockAcquire(lock, LW_EXCLUSIVE);
 
    /* Zero the page */
    SimpleLruZeroPage(SubTransCtl, pageno);
 
    LWLockRelease(lock);
}

References FirstNormalTransactionId, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SimpleLruGetBankLock(), SimpleLruZeroPage(), SubTransCtl, TransactionIdEquals, TransactionIdToEntry, and TransactionIdToPage().

Referenced by GetNewTransactionId(), ProcArrayApplyRecoveryInfo(), and RecordKnownAssignedTransactionIds().

StartupSUBTRANS()

void StartupSUBTRANS

(

TransactionId

oldestActiveXID

)

Definition at line 283 of file subtrans.c.

{
    FullTransactionId nextXid;
    int64       startPage;
    int64       endPage;
    LWLock     *prevlock = NULL;
    LWLock     *lock;
 
    /*
     * 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.
     */
    startPage = TransactionIdToPage(oldestActiveXID);
    nextXid = TransamVariables->nextXid;
    endPage = TransactionIdToPage(XidFromFullTransactionId(nextXid));
 
    for (;;)
    {
        lock = SimpleLruGetBankLock(SubTransCtl, startPage);
        if (prevlock != lock)
        {
            if (prevlock)
                LWLockRelease(prevlock);
            LWLockAcquire(lock, LW_EXCLUSIVE);
            prevlock = lock;
        }
 
        (void) SimpleLruZeroPage(SubTransCtl, startPage);
        if (startPage == endPage)
            break;
 
        startPage++;
        /* must account for wraparound */
        if (startPage > TransactionIdToPage(MaxTransactionId))
            startPage = 0;
    }
 
    LWLockRelease(lock);
}

References LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), MaxTransactionId, TransamVariablesData::nextXid, SimpleLruGetBankLock(), SimpleLruZeroPage(), SubTransCtl, TransactionIdToPage(), TransamVariables, and XidFromFullTransactionId.

Referenced by StartupXLOG().

SubTransGetParent()

TransactionId SubTransGetParent

(

TransactionId

xid

)

Definition at line 121 of file subtrans.c.

{
    int64       pageno = TransactionIdToPage(xid);
    int         entryno = TransactionIdToEntry(xid);
    int         slotno;
    TransactionId *ptr;
    TransactionId parent;
 
    /* Can't ask about stuff that might not be around anymore */
    Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
 
    /* Bootstrap and frozen XIDs have no parent */
    if (!TransactionIdIsNormal(xid))
        return InvalidTransactionId;
 
    /* lock is acquired by SimpleLruReadPage_ReadOnly */
 
    slotno = SimpleLruReadPage_ReadOnly(SubTransCtl, pageno, xid);
    ptr = (TransactionId *) SubTransCtl->shared->page_buffer[slotno];
    ptr += entryno;
 
    parent = *ptr;
 
    LWLockRelease(SimpleLruGetBankLock(SubTransCtl, pageno));
 
    return parent;
}

References Assert(), InvalidTransactionId, LWLockRelease(), SimpleLruGetBankLock(), SimpleLruReadPage_ReadOnly(), SubTransCtl, TransactionIdFollowsOrEquals(), TransactionIdIsNormal, TransactionIdToEntry, TransactionIdToPage(), and TransactionXmin.

Referenced by SubTransGetTopmostTransaction(), TransactionIdDidAbort(), and TransactionIdDidCommit().

SubTransGetTopmostTransaction()

TransactionId SubTransGetTopmostTransaction

(

TransactionId

xid

)

Definition at line 162 of file subtrans.c.

{
    TransactionId parentXid = xid,
                previousXid = xid;
 
    /* Can't ask about stuff that might not be around anymore */
    Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));
 
    while (TransactionIdIsValid(parentXid))
    {
        previousXid = parentXid;
        if (TransactionIdPrecedes(parentXid, TransactionXmin))
            break;
        parentXid = SubTransGetParent(parentXid);
 
        /*
         * By convention the parent xid gets allocated first, so should always
         * precede the child xid. Anything else points to a corrupted data
         * structure that could lead to an infinite loop, so exit.
         */
        if (!TransactionIdPrecedes(parentXid, previousXid))
            elog(ERROR, "pg_subtrans contains invalid entry: xid %u points to parent xid %u",
                 previousXid, parentXid);
    }
 
    Assert(TransactionIdIsValid(previousXid));
 
    return previousXid;
}

References Assert(), elog, ERROR, SubTransGetParent(), TransactionIdFollowsOrEquals(), TransactionIdIsValid, TransactionIdPrecedes(), and TransactionXmin.

Referenced by ConditionalXactLockTableWait(), HeapCheckForSerializableConflictOut(), TransactionIdIsInProgress(), XactLockTableWait(), and XidInMVCCSnapshot().

SubTransSetParent()

void SubTransSetParent	(	TransactionId	xid,
		TransactionId	parent
	)

Definition at line 84 of file subtrans.c.

{
    int64       pageno = TransactionIdToPage(xid);
    int         entryno = TransactionIdToEntry(xid);
    int         slotno;
    LWLock     *lock;
    TransactionId *ptr;
 
    Assert(TransactionIdIsValid(parent));
    Assert(TransactionIdFollows(xid, parent));
 
    lock = SimpleLruGetBankLock(SubTransCtl, pageno);
    LWLockAcquire(lock, LW_EXCLUSIVE);
 
    slotno = SimpleLruReadPage(SubTransCtl, pageno, true, xid);
    ptr = (TransactionId *) SubTransCtl->shared->page_buffer[slotno];
    ptr += entryno;
 
    /*
     * It's possible we'll try to set the parent xid multiple times but we
     * shouldn't ever be changing the xid from one valid xid to another valid
     * xid, which would corrupt the data structure.
     */
    if (*ptr != parent)
    {
        Assert(*ptr == InvalidTransactionId);
        *ptr = parent;
        SubTransCtl->shared->page_dirty[slotno] = true;
    }
 
    LWLockRelease(lock);
}

References Assert(), if(), InvalidTransactionId, LW_EXCLUSIVE, LWLockAcquire(), LWLockRelease(), SimpleLruGetBankLock(), SimpleLruReadPage(), SubTransCtl, TransactionIdFollows(), TransactionIdIsValid, TransactionIdToEntry, and TransactionIdToPage().

Referenced by AssignTransactionId(), ProcArrayApplyXidAssignment(), and ProcessTwoPhaseBuffer().

SUBTRANSShmemInit()

void SUBTRANSShmemInit

(

void

)

Definition at line 219 of file subtrans.c.

{
    /* If auto-tuning is requested, now is the time to do it */
    if (subtransaction_buffers == 0)
    {
        char        buf[32];
 
        snprintf(buf, sizeof(buf), "%d", SUBTRANSShmemBuffers());
        SetConfigOption("subtransaction_buffers", buf, PGC_POSTMASTER,
                        PGC_S_DYNAMIC_DEFAULT);
 
        /*
         * We prefer to report this value's source as PGC_S_DYNAMIC_DEFAULT.
         * However, if the DBA explicitly set subtransaction_buffers = 0 in
         * the config file, then PGC_S_DYNAMIC_DEFAULT will fail to override
         * that and we must force the matter with PGC_S_OVERRIDE.
         */
        if (subtransaction_buffers == 0)    /* failed to apply it? */
            SetConfigOption("subtransaction_buffers", buf, PGC_POSTMASTER,
                            PGC_S_OVERRIDE);
    }
    Assert(subtransaction_buffers != 0);
 
    SubTransCtl->PagePrecedes = SubTransPagePrecedes;
    SimpleLruInit(SubTransCtl, "subtransaction", SUBTRANSShmemBuffers(), 0,
                  "pg_subtrans", LWTRANCHE_SUBTRANS_BUFFER,
                  LWTRANCHE_SUBTRANS_SLRU, SYNC_HANDLER_NONE, false);
    SlruPagePrecedesUnitTests(SubTransCtl, SUBTRANS_XACTS_PER_PAGE);
}

References Assert(), buf, PGC_POSTMASTER, PGC_S_DYNAMIC_DEFAULT, PGC_S_OVERRIDE, SetConfigOption(), SimpleLruInit(), SlruPagePrecedesUnitTests, snprintf, SUBTRANS_XACTS_PER_PAGE, subtransaction_buffers, SubTransCtl, SubTransPagePrecedes(), SUBTRANSShmemBuffers(), and SYNC_HANDLER_NONE.

Referenced by CreateOrAttachShmemStructs().

SUBTRANSShmemSize()

Size SUBTRANSShmemSize

(

void

)

Definition at line 213 of file subtrans.c.

{
    return SimpleLruShmemSize(SUBTRANSShmemBuffers(), 0);
}

References SimpleLruShmemSize(), and SUBTRANSShmemBuffers().

Referenced by CalculateShmemSize().

TruncateSUBTRANS()

void TruncateSUBTRANS

(

TransactionId

oldestXact

)

Definition at line 385 of file subtrans.c.

{
    int64       cutoffPage;
 
    /*
     * The cutoff point is the start of the segment containing oldestXact. We
     * pass the *page* containing oldestXact to SimpleLruTruncate.  We step
     * back one transaction to avoid passing a cutoff page that hasn't been
     * created yet in the rare case that oldestXact would be the first item on
     * a page and oldestXact == next XID.  In that case, if we didn't subtract
     * one, we'd trigger SimpleLruTruncate's wraparound detection.
     */
    TransactionIdRetreat(oldestXact);
    cutoffPage = TransactionIdToPage(oldestXact);
 
    SimpleLruTruncate(SubTransCtl, cutoffPage);
}

References SimpleLruTruncate(), SubTransCtl, TransactionIdRetreat, and TransactionIdToPage().

Referenced by CreateCheckPoint(), and CreateRestartPoint().