/*------------------------------------------------------------------------- * * nodeLockRows.c * Routines to handle FOR UPDATE/FOR SHARE row locking * * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/executor/nodeLockRows.c * *------------------------------------------------------------------------- */ /* * INTERFACE ROUTINES * ExecLockRows - fetch locked rows * ExecInitLockRows - initialize node and subnodes.. * ExecEndLockRows - shutdown node and subnodes */ #include "postgres.h" #include "access/tableam.h" #include "access/xact.h" #include "executor/executor.h" #include "executor/nodeLockRows.h" #include "foreign/fdwapi.h" #include "miscadmin.h" #include "utils/rel.h" /* ---------------------------------------------------------------- * ExecLockRows * ---------------------------------------------------------------- */ static TupleTableSlot * /* return: a tuple or NULL */ ExecLockRows(PlanState *pstate) { LockRowsState *node = castNode(LockRowsState, pstate); TupleTableSlot *slot; EState *estate; PlanState *outerPlan; bool epq_needed; ListCell *lc; CHECK_FOR_INTERRUPTS(); /* * get information from the node */ estate = node->ps.state; outerPlan = outerPlanState(node); /* * Get next tuple from subplan, if any. */ lnext: slot = ExecProcNode(outerPlan); if (TupIsNull(slot)) { /* Release any resources held by EPQ mechanism before exiting */ EvalPlanQualEnd(&node->lr_epqstate); return NULL; } /* We don't need EvalPlanQual unless we get updated tuple version(s) */ epq_needed = false; /* * Attempt to lock the source tuple(s). (Note we only have locking * rowmarks in lr_arowMarks.) */ foreach(lc, node->lr_arowMarks) { ExecAuxRowMark *aerm = (ExecAuxRowMark *) lfirst(lc); ExecRowMark *erm = aerm->rowmark; Datum datum; bool isNull; ItemPointerData tid; TM_FailureData tmfd; LockTupleMode lockmode; int lockflags = 0; TM_Result test; TupleTableSlot *markSlot; /* clear any leftover test tuple for this rel */ markSlot = EvalPlanQualSlot(&node->lr_epqstate, erm->relation, erm->rti); ExecClearTuple(markSlot); /* if child rel, must check whether it produced this row */ if (erm->rti != erm->prti) { Oid tableoid; datum = ExecGetJunkAttribute(slot, aerm->toidAttNo, &isNull); /* shouldn't ever get a null result... */ if (isNull) elog(ERROR, "tableoid is NULL"); tableoid = DatumGetObjectId(datum); Assert(OidIsValid(erm->relid)); if (tableoid != erm->relid) { /* this child is inactive right now */ erm->ermActive = false; ItemPointerSetInvalid(&(erm->curCtid)); ExecClearTuple(markSlot); continue; } } erm->ermActive = true; /* fetch the tuple's ctid */ datum = ExecGetJunkAttribute(slot, aerm->ctidAttNo, &isNull); /* shouldn't ever get a null result... */ if (isNull) elog(ERROR, "ctid is NULL"); /* requests for foreign tables must be passed to their FDW */ if (erm->relation->rd_rel->relkind == RELKIND_FOREIGN_TABLE) { FdwRoutine *fdwroutine; bool updated = false; fdwroutine = GetFdwRoutineForRelation(erm->relation, false); /* this should have been checked already, but let's be safe */ if (fdwroutine->RefetchForeignRow == NULL) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("cannot lock rows in foreign table \"%s\"", RelationGetRelationName(erm->relation)))); fdwroutine->RefetchForeignRow(estate, erm, datum, markSlot, &updated); if (TupIsNull(markSlot)) { /* couldn't get the lock, so skip this row */ goto lnext; } /* * if FDW says tuple was updated before getting locked, we need to * perform EPQ testing to see if quals are still satisfied */ if (updated) epq_needed = true; continue; } /* okay, try to lock (and fetch) the tuple */ tid = *((ItemPointer) DatumGetPointer(datum)); switch (erm->markType) { case ROW_MARK_EXCLUSIVE: lockmode = LockTupleExclusive; break; case ROW_MARK_NOKEYEXCLUSIVE: lockmode = LockTupleNoKeyExclusive; break; case ROW_MARK_SHARE: lockmode = LockTupleShare; break; case ROW_MARK_KEYSHARE: lockmode = LockTupleKeyShare; break; default: elog(ERROR, "unsupported rowmark type"); lockmode = LockTupleNoKeyExclusive; /* keep compiler quiet */ break; } lockflags = TUPLE_LOCK_FLAG_LOCK_UPDATE_IN_PROGRESS; if (!IsolationUsesXactSnapshot()) lockflags |= TUPLE_LOCK_FLAG_FIND_LAST_VERSION; test = table_tuple_lock(erm->relation, &tid, estate->es_snapshot, markSlot, estate->es_output_cid, lockmode, erm->waitPolicy, lockflags, &tmfd); switch (test) { case TM_WouldBlock: /* couldn't lock tuple in SKIP LOCKED mode */ goto lnext; case TM_SelfModified: /* * The target tuple was already updated or deleted by the * current command, or by a later command in the current * transaction. We *must* ignore the tuple in the former * case, so as to avoid the "Halloween problem" of repeated * update attempts. In the latter case it might be sensible * to fetch the updated tuple instead, but doing so would * require changing heap_update and heap_delete to not * complain about updating "invisible" tuples, which seems * pretty scary (table_tuple_lock will not complain, but few * callers expect TM_Invisible, and we're not one of them). So * for now, treat the tuple as deleted and do not process. */ goto lnext; case TM_Ok: /* * Got the lock successfully, the locked tuple saved in * markSlot for, if needed, EvalPlanQual testing below. */ if (tmfd.traversed) epq_needed = true; break; case TM_Updated: if (IsolationUsesXactSnapshot()) ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to concurrent update"))); elog(ERROR, "unexpected table_tuple_lock status: %u", test); break; case TM_Deleted: if (IsolationUsesXactSnapshot()) ereport(ERROR, (errcode(ERRCODE_T_R_SERIALIZATION_FAILURE), errmsg("could not serialize access due to concurrent update"))); /* tuple was deleted so don't return it */ goto lnext; case TM_Invisible: elog(ERROR, "attempted to lock invisible tuple"); break; default: elog(ERROR, "unrecognized table_tuple_lock status: %u", test); } /* Remember locked tuple's TID for EPQ testing and WHERE CURRENT OF */ erm->curCtid = tid; } /* * If we need to do EvalPlanQual testing, do so. */ if (epq_needed) { /* Initialize EPQ machinery */ EvalPlanQualBegin(&node->lr_epqstate); /* * To fetch non-locked source rows the EPQ logic needs to access junk * columns from the tuple being tested. */ EvalPlanQualSetSlot(&node->lr_epqstate, slot); /* * And finally we can re-evaluate the tuple. */ slot = EvalPlanQualNext(&node->lr_epqstate); if (TupIsNull(slot)) { /* Updated tuple fails qual, so ignore it and go on */ goto lnext; } } /* Got all locks, so return the current tuple */ return slot; } /* ---------------------------------------------------------------- * ExecInitLockRows * * This initializes the LockRows node state structures and * the node's subplan. * ---------------------------------------------------------------- */ LockRowsState * ExecInitLockRows(LockRows *node, EState *estate, int eflags) { LockRowsState *lrstate; Plan *outerPlan = outerPlan(node); List *epq_arowmarks; ListCell *lc; /* check for unsupported flags */ Assert(!(eflags & EXEC_FLAG_MARK)); /* * create state structure */ lrstate = makeNode(LockRowsState); lrstate->ps.plan = (Plan *) node; lrstate->ps.state = estate; lrstate->ps.ExecProcNode = ExecLockRows; /* * Miscellaneous initialization * * LockRows nodes never call ExecQual or ExecProject, therefore no * ExprContext is needed. */ /* * Initialize result type. */ ExecInitResultTypeTL(&lrstate->ps); /* * then initialize outer plan */ outerPlanState(lrstate) = ExecInitNode(outerPlan, estate, eflags); /* node returns unmodified slots from the outer plan */ lrstate->ps.resultopsset = true; lrstate->ps.resultops = ExecGetResultSlotOps(outerPlanState(lrstate), &lrstate->ps.resultopsfixed); /* * LockRows nodes do no projections, so initialize projection info for * this node appropriately */ lrstate->ps.ps_ProjInfo = NULL; /* * Locate the ExecRowMark(s) that this node is responsible for, and * construct ExecAuxRowMarks for them. (InitPlan should already have * built the global list of ExecRowMarks.) */ lrstate->lr_arowMarks = NIL; epq_arowmarks = NIL; foreach(lc, node->rowMarks) { PlanRowMark *rc = lfirst_node(PlanRowMark, lc); ExecRowMark *erm; ExecAuxRowMark *aerm; /* ignore "parent" rowmarks; they are irrelevant at runtime */ if (rc->isParent) continue; /* find ExecRowMark and build ExecAuxRowMark */ erm = ExecFindRowMark(estate, rc->rti, false); aerm = ExecBuildAuxRowMark(erm, outerPlan->targetlist); /* * Only locking rowmarks go into our own list. Non-locking marks are * passed off to the EvalPlanQual machinery. This is because we don't * want to bother fetching non-locked rows unless we actually have to * do an EPQ recheck. */ if (RowMarkRequiresRowShareLock(erm->markType)) lrstate->lr_arowMarks = lappend(lrstate->lr_arowMarks, aerm); else epq_arowmarks = lappend(epq_arowmarks, aerm); } /* Now we have the info needed to set up EPQ state */ EvalPlanQualInit(&lrstate->lr_epqstate, estate, outerPlan, epq_arowmarks, node->epqParam); return lrstate; } /* ---------------------------------------------------------------- * ExecEndLockRows * * This shuts down the subplan and frees resources allocated * to this node. * ---------------------------------------------------------------- */ void ExecEndLockRows(LockRowsState *node) { /* We may have shut down EPQ already, but no harm in another call */ EvalPlanQualEnd(&node->lr_epqstate); ExecEndNode(outerPlanState(node)); } void ExecReScanLockRows(LockRowsState *node) { /* * if chgParam of subnode is not null then plan will be re-scanned by * first ExecProcNode. */ if (node->ps.lefttree->chgParam == NULL) ExecReScan(node->ps.lefttree); }