Query in SQL function still not schema-safe; add a couple

[PostgreSQL.git] / src / backend / access / transam / transam.c

/*-------------------------------------------------------------------------
 *
 * transam.c
 *        postgres transaction log interface routines
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *        $PostgreSQL$
 *
 * NOTES
 *        This file contains the high level access-method interface to the
 *        transaction system.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "access/clog.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "utils/snapmgr.h"


/*
 * Single-item cache for results of TransactionLogFetch.  It's worth having
 * such a cache because we frequently find ourselves repeatedly checking the
 * same XID, for example when scanning a table just after a bulk insert,
 * update, or delete.
 */
static TransactionId cachedFetchXid = InvalidTransactionId;
static XidStatus cachedFetchXidStatus;
static XLogRecPtr cachedCommitLSN;

/* Handy constant for an invalid xlog recptr */
static const XLogRecPtr InvalidXLogRecPtr = {0, 0};

/* Local functions */
static XidStatus TransactionLogFetch(TransactionId transactionId);


/* ----------------------------------------------------------------
 *              Postgres log access method interface
 *
 *              TransactionLogFetch
 * ----------------------------------------------------------------
 */

/*
 * TransactionLogFetch --- fetch commit status of specified transaction id
 */
static XidStatus
TransactionLogFetch(TransactionId transactionId)
{
        XidStatus       xidstatus;
        XLogRecPtr      xidlsn;

        /*
         * Before going to the commit log manager, check our single item cache to
         * see if we didn't just check the transaction status a moment ago.
         */
        if (TransactionIdEquals(transactionId, cachedFetchXid))
                return cachedFetchXidStatus;

        /*
         * Also, check to see if the transaction ID is a permanent one.
         */
        if (!TransactionIdIsNormal(transactionId))
        {
                if (TransactionIdEquals(transactionId, BootstrapTransactionId))
                        return TRANSACTION_STATUS_COMMITTED;
                if (TransactionIdEquals(transactionId, FrozenTransactionId))
                        return TRANSACTION_STATUS_COMMITTED;
                return TRANSACTION_STATUS_ABORTED;
        }

        /*
         * Get the transaction status.
         */
        xidstatus = TransactionIdGetStatus(transactionId, &xidlsn);

        /*
         * Cache it, but DO NOT cache status for unfinished or sub-committed
         * transactions!  We only cache status that is guaranteed not to change.
         */
        if (xidstatus != TRANSACTION_STATUS_IN_PROGRESS &&
                xidstatus != TRANSACTION_STATUS_SUB_COMMITTED)
        {
                cachedFetchXid = transactionId;
                cachedFetchXidStatus = xidstatus;
                cachedCommitLSN = xidlsn;
        }

        return xidstatus;
}

/* ----------------------------------------------------------------
 *                                              Interface functions
 *
 *              TransactionIdDidCommit
 *              TransactionIdDidAbort
 *              ========
 *                 these functions test the transaction status of
 *                 a specified transaction id.
 *
 *              TransactionIdCommitTree
 *              TransactionIdAsyncCommitTree
 *              TransactionIdAbortTree
 *              ========
 *                 these functions set the transaction status of the specified
 *                 transaction tree.
 *
 * See also TransactionIdIsInProgress, which once was in this module
 * but now lives in procarray.c.
 * ----------------------------------------------------------------
 */

/*
 * TransactionIdDidCommit
 *              True iff transaction associated with the identifier did commit.
 *
 * Note:
 *              Assumes transaction identifier is valid.
 */
bool                                                    /* true if given transaction committed */
TransactionIdDidCommit(TransactionId transactionId)
{
        XidStatus       xidstatus;

        xidstatus = TransactionLogFetch(transactionId);

        /*
         * If it's marked committed, it's committed.
         */
        if (xidstatus == TRANSACTION_STATUS_COMMITTED)
                return true;

        /*
         * If it's marked subcommitted, we have to check the parent recursively.
         * However, if it's older than TransactionXmin, we can't look at
         * pg_subtrans; instead assume that the parent crashed without cleaning up
         * its children.
         *
         * Originally we Assert'ed that the result of SubTransGetParent was not
         * zero. However with the introduction of prepared transactions, there can
         * be a window just after database startup where we do not have complete
         * knowledge in pg_subtrans of the transactions after TransactionXmin.
         * StartupSUBTRANS() has ensured that any missing information will be
         * zeroed.      Since this case should not happen under normal conditions, it
         * seems reasonable to emit a WARNING for it.
         */
        if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
        {
                TransactionId parentXid;

                if (TransactionIdPrecedes(transactionId, TransactionXmin))
                        return false;
                parentXid = SubTransGetParent(transactionId);
                if (!TransactionIdIsValid(parentXid))
                {
                        elog(WARNING, "no pg_subtrans entry for subcommitted XID %u",
                                 transactionId);
                        return false;
                }
                return TransactionIdDidCommit(parentXid);
        }

        /*
         * It's not committed.
         */
        return false;
}

/*
 * TransactionIdDidAbort
 *              True iff transaction associated with the identifier did abort.
 *
 * Note:
 *              Assumes transaction identifier is valid.
 */
bool                                                    /* true if given transaction aborted */
TransactionIdDidAbort(TransactionId transactionId)
{
        XidStatus       xidstatus;

        xidstatus = TransactionLogFetch(transactionId);

        /*
         * If it's marked aborted, it's aborted.
         */
        if (xidstatus == TRANSACTION_STATUS_ABORTED)
                return true;

        /*
         * If it's marked subcommitted, we have to check the parent recursively.
         * However, if it's older than TransactionXmin, we can't look at
         * pg_subtrans; instead assume that the parent crashed without cleaning up
         * its children.
         */
        if (xidstatus == TRANSACTION_STATUS_SUB_COMMITTED)
        {
                TransactionId parentXid;

                if (TransactionIdPrecedes(transactionId, TransactionXmin))
                        return true;
                parentXid = SubTransGetParent(transactionId);
                if (!TransactionIdIsValid(parentXid))
                {
                        /* see notes in TransactionIdDidCommit */
                        elog(WARNING, "no pg_subtrans entry for subcommitted XID %u",
                                 transactionId);
                        return true;
                }
                return TransactionIdDidAbort(parentXid);
        }

        /*
         * It's not aborted.
         */
        return false;
}

/*
 * TransactionIdIsKnownCompleted
 *              True iff transaction associated with the identifier is currently
 *              known to have either committed or aborted.
 *
 * This does NOT look into pg_clog but merely probes our local cache
 * (and so it's not named TransactionIdDidComplete, which would be the
 * appropriate name for a function that worked that way).  The intended
 * use is just to short-circuit TransactionIdIsInProgress calls when doing
 * repeated tqual.c checks for the same XID.  If this isn't extremely fast
 * then it will be counterproductive.
 *
 * Note:
 *              Assumes transaction identifier is valid.
 */
bool
TransactionIdIsKnownCompleted(TransactionId transactionId)
{
        if (TransactionIdEquals(transactionId, cachedFetchXid))
        {
                /* If it's in the cache at all, it must be completed. */
                return true;
        }

        return false;
}

/*
 * TransactionIdCommitTree
 *              Marks the given transaction and children as committed
 *
 * "xid" is a toplevel transaction commit, and the xids array contains its
 * committed subtransactions.
 *
 * This commit operation is not guaranteed to be atomic, but if not, subxids
 * are correctly marked subcommit first.
 */
void
TransactionIdCommitTree(TransactionId xid, int nxids, TransactionId *xids)
{
        TransactionIdSetTreeStatus(xid, nxids, xids,
                                                           TRANSACTION_STATUS_COMMITTED,
                                                           InvalidXLogRecPtr);
}

/*
 * TransactionIdAsyncCommitTree
 *              Same as above, but for async commits.  The commit record LSN is needed.
 */
void
TransactionIdAsyncCommitTree(TransactionId xid, int nxids, TransactionId *xids,
                                                         XLogRecPtr lsn)
{
        TransactionIdSetTreeStatus(xid, nxids, xids,
                                                           TRANSACTION_STATUS_COMMITTED, lsn);
}

/*
 * TransactionIdAbortTree
 *              Marks the given transaction and children as aborted.
 *
 * "xid" is a toplevel transaction commit, and the xids array contains its
 * committed subtransactions.
 *
 * We don't need to worry about the non-atomic behavior, since any onlookers
 * will consider all the xacts as not-yet-committed anyway.
 */
void
TransactionIdAbortTree(TransactionId xid, int nxids, TransactionId *xids)
{
        TransactionIdSetTreeStatus(xid, nxids, xids,
                                                           TRANSACTION_STATUS_ABORTED, InvalidXLogRecPtr);
}

/*
 * TransactionIdPrecedes --- is id1 logically < id2?
 */
bool
TransactionIdPrecedes(TransactionId id1, TransactionId id2)
{
        /*
         * If either ID is a permanent XID then we can just do unsigned
         * comparison.  If both are normal, do a modulo-2^31 comparison.
         */
        int32           diff;

        if (!TransactionIdIsNormal(id1) || !TransactionIdIsNormal(id2))
                return (id1 < id2);

        diff = (int32) (id1 - id2);
        return (diff < 0);
}

/*
 * TransactionIdPrecedesOrEquals --- is id1 logically <= id2?
 */
bool
TransactionIdPrecedesOrEquals(TransactionId id1, TransactionId id2)
{
        int32           diff;

        if (!TransactionIdIsNormal(id1) || !TransactionIdIsNormal(id2))
                return (id1 <= id2);

        diff = (int32) (id1 - id2);
        return (diff <= 0);
}

/*
 * TransactionIdFollows --- is id1 logically > id2?
 */
bool
TransactionIdFollows(TransactionId id1, TransactionId id2)
{
        int32           diff;

        if (!TransactionIdIsNormal(id1) || !TransactionIdIsNormal(id2))
                return (id1 > id2);

        diff = (int32) (id1 - id2);
        return (diff > 0);
}

/*
 * TransactionIdFollowsOrEquals --- is id1 logically >= id2?
 */
bool
TransactionIdFollowsOrEquals(TransactionId id1, TransactionId id2)
{
        int32           diff;

        if (!TransactionIdIsNormal(id1) || !TransactionIdIsNormal(id2))
                return (id1 >= id2);

        diff = (int32) (id1 - id2);
        return (diff >= 0);
}


/*
 * TransactionIdLatest --- get latest XID among a main xact and its children
 */
TransactionId
TransactionIdLatest(TransactionId mainxid,
                                        int nxids, const TransactionId *xids)
{
        TransactionId result;

        /*
         * In practice it is highly likely that the xids[] array is sorted, and so
         * we could save some cycles by just taking the last child XID, but this
         * probably isn't so performance-critical that it's worth depending on
         * that assumption.  But just to show we're not totally stupid, scan the
         * array back-to-front to avoid useless assignments.
         */
        result = mainxid;
        while (--nxids >= 0)
        {
                if (TransactionIdPrecedes(result, xids[nxids]))
                        result = xids[nxids];
        }
        return result;
}


/*
 * TransactionIdGetCommitLSN
 *
 * This function returns an LSN that is late enough to be able
 * to guarantee that if we flush up to the LSN returned then we
 * will have flushed the transaction's commit record to disk.
 *
 * The result is not necessarily the exact LSN of the transaction's
 * commit record!  For example, for long-past transactions (those whose
 * clog pages already migrated to disk), we'll return InvalidXLogRecPtr.
 * Also, because we group transactions on the same clog page to conserve
 * storage, we might return the LSN of a later transaction that falls into
 * the same group.
 */
XLogRecPtr
TransactionIdGetCommitLSN(TransactionId xid)
{
        XLogRecPtr      result;

        /*
         * Currently, all uses of this function are for xids that were just
         * reported to be committed by TransactionLogFetch, so we expect that
         * checking TransactionLogFetch's cache will usually succeed and avoid an
         * extra trip to shared memory.
         */
        if (TransactionIdEquals(xid, cachedFetchXid))
                return cachedCommitLSN;

        /* Special XIDs are always known committed */
        if (!TransactionIdIsNormal(xid))
                return InvalidXLogRecPtr;

        /*
         * Get the transaction status.
         */
        (void) TransactionIdGetStatus(xid, &result);

        return result;
}