/*
* txid_current_snapshot() returns txid_snapshot
*
* Return current snapshot in TXID format
*
* Note that only top-transaction XIDs are included in the snapshot.
*/
Datum
txid_current_snapshot(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap;
uint32 nxip,
i,
size;
TxidEpoch state;
Snapshot cur;
cur = GetActiveSnapshot();
if (cur == NULL)
elog(ERROR, "no active snapshot set");
load_xid_epoch(&state);
/* allocate */
nxip = cur->xcnt;
size = TXID_SNAPSHOT_SIZE(nxip);
snap = palloc(size);
SET_VARSIZE(snap, size);
/* fill */
snap->xmin = convert_xid(cur->xmin, &state);
snap->xmax = convert_xid(cur->xmax, &state);
snap->nxip = nxip;
for (i = 0; i < nxip; i++)
snap->xip[i] = convert_xid(cur->xip[i], &state);
/* we want them guaranteed to be in ascending order */
sort_snapshot(snap);
PG_RETURN_POINTER(snap);
}
/*
* txid_current() returns int8
*
* Return the current toplevel transaction ID as TXID
*/
Datum
txid_current(PG_FUNCTION_ARGS)
{
txid val;
TxidEpoch state;
load_xid_epoch(&state);
val = convert_xid(GetTopTransactionId(), &state);
PG_RETURN_INT64(val);
}
/*
* txid_current_snapshot() returns txid_snapshot
*
* Return current snapshot in TXID format
*
* Note that only top-transaction XIDs are included in the snapshot.
*/
Datum
txid_current_snapshot(PG_FUNCTION_ARGS)
{
TxidSnapshot *snap;
uint32 nxip,
i;
TxidEpoch state;
Snapshot cur;
cur = GetActiveSnapshot();
if (cur == NULL)
elog(ERROR, "no active snapshot set");
load_xid_epoch(&state);
/*
* Compile-time limits on the procarray (MAX_BACKENDS processes plus
* MAX_BACKENDS prepared transactions) guarantee nxip won't be too large.
*/
StaticAssertStmt(MAX_BACKENDS * 2 <= TXID_SNAPSHOT_MAX_NXIP,
"possible overflow in txid_current_snapshot()");
/* allocate */
nxip = cur->xcnt;
snap = palloc(TXID_SNAPSHOT_SIZE(nxip));
/* fill */
snap->xmin = convert_xid(cur->xmin, &state);
snap->xmax = convert_xid(cur->xmax, &state);
snap->nxip = nxip;
for (i = 0; i < nxip; i++)
snap->xip[i] = convert_xid(cur->xip[i], &state);
/*
* We want them guaranteed to be in ascending order. This also removes
* any duplicate xids. Normally, an XID can only be assigned to one
* backend, but when preparing a transaction for two-phase commit, there
* is a transient state when both the original backend and the dummy
* PGPROC entry reserved for the prepared transaction hold the same XID.
*/
sort_snapshot(snap);
/* set size after sorting, because it may have removed duplicate xips */
SET_VARSIZE(snap, TXID_SNAPSHOT_SIZE(snap->nxip));
PG_RETURN_POINTER(snap);
}
/*
* txid_current() returns int8
*
* Return the current toplevel transaction ID as TXID
* If the current transaction does not have one, one is assigned.
*/
Datum
txid_current(PG_FUNCTION_ARGS)
{
txid val;
TxidEpoch state;
/*
* Must prevent during recovery because if an xid is not assigned we try
* to assign one, which would fail. Programs already rely on this function
* to always return a valid current xid, so we should not change this to
* return NULL or similar invalid xid.
*/
PreventCommandDuringRecovery("txid_current()");
load_xid_epoch(&state);
val = convert_xid(GetTopTransactionId(), &state);
PG_RETURN_INT64(val);
}