mirror of https://github.com/postgres/postgres
Along the way, allow FOR UPDATE in non-WITH-HOLD cursors; there may once have been a reason to disallow that, but it seems to work now, and it's really rather necessary if you want to select a row via a cursor and then update it in a concurrent-safe fashion. Original patch by Arul Shaji, rather heavily editorialized by Tom Lane.REL8_3_STABLE
Tom Lane
19 years ago
parent
85d72f0516
commit
6808f1b1de
@ -0,0 +1,185 @@ |
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/*-------------------------------------------------------------------------
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* |
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* execCurrent.c |
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* executor support for WHERE CURRENT OF cursor |
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* |
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group |
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* Portions Copyright (c) 1994, Regents of the University of California |
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* |
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* $PostgreSQL: pgsql/src/backend/executor/execCurrent.c,v 1.1 2007/06/11 01:16:22 tgl Exp $ |
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* |
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*------------------------------------------------------------------------- |
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*/ |
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#include "postgres.h" |
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#include "executor/executor.h" |
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#include "utils/lsyscache.h" |
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#include "utils/portal.h" |
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static ScanState *search_plan_tree(PlanState *node, Oid table_oid); |
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/*
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* execCurrentOf |
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* |
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* Given the name of a cursor and the OID of a table, determine which row |
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* of the table is currently being scanned by the cursor, and return its |
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* TID into *current_tid. |
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* |
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* Returns TRUE if a row was identified. Returns FALSE if the cursor is valid |
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* for the table but is not currently scanning a row of the table (this is a |
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* legal situation in inheritance cases). Raises error if cursor is not a |
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* valid updatable scan of the specified table. |
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*/ |
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bool |
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execCurrentOf(char *cursor_name, Oid table_oid, |
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ItemPointer current_tid) |
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{ |
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char *table_name; |
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Portal portal; |
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QueryDesc *queryDesc; |
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ScanState *scanstate; |
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HeapTuple tup; |
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/* Fetch table name for possible use in error messages */ |
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table_name = get_rel_name(table_oid); |
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if (table_name == NULL) |
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elog(ERROR, "cache lookup failed for relation %u", table_oid); |
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/* Find the cursor's portal */ |
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portal = GetPortalByName(cursor_name); |
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if (!PortalIsValid(portal)) |
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ereport(ERROR, |
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(errcode(ERRCODE_UNDEFINED_CURSOR), |
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errmsg("cursor \"%s\" does not exist", cursor_name))); |
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/*
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* We have to watch out for non-SELECT queries as well as held cursors, |
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* both of which may have null queryDesc. |
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*/ |
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if (portal->strategy != PORTAL_ONE_SELECT) |
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ereport(ERROR, |
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(errcode(ERRCODE_INVALID_CURSOR_STATE), |
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errmsg("cursor \"%s\" is not a SELECT query", |
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cursor_name))); |
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queryDesc = PortalGetQueryDesc(portal); |
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if (queryDesc == NULL) |
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ereport(ERROR, |
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(errcode(ERRCODE_INVALID_CURSOR_STATE), |
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errmsg("cursor \"%s\" is held from a previous transaction", |
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cursor_name))); |
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/*
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* Dig through the cursor's plan to find the scan node. Fail if it's |
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* not there or buried underneath aggregation. |
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*/ |
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scanstate = search_plan_tree(ExecGetActivePlanTree(queryDesc), |
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table_oid); |
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if (!scanstate) |
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ereport(ERROR, |
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(errcode(ERRCODE_INVALID_CURSOR_STATE), |
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errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", |
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cursor_name, table_name))); |
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/*
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* The cursor must have a current result row: per the SQL spec, it's |
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* an error if not. We test this at the top level, rather than at |
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* the scan node level, because in inheritance cases any one table |
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* scan could easily not be on a row. We want to return false, not |
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* raise error, if the passed-in table OID is for one of the inactive |
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* scans. |
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*/ |
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if (portal->atStart || portal->atEnd) |
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ereport(ERROR, |
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(errcode(ERRCODE_INVALID_CURSOR_STATE), |
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errmsg("cursor \"%s\" is not positioned on a row", |
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cursor_name))); |
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/* Now OK to return false if we found an inactive scan */ |
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if (TupIsNull(scanstate->ss_ScanTupleSlot)) |
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return false; |
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tup = scanstate->ss_ScanTupleSlot->tts_tuple; |
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if (tup == NULL) |
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elog(ERROR, "CURRENT OF applied to non-materialized tuple"); |
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Assert(tup->t_tableOid == table_oid); |
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*current_tid = tup->t_self; |
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return true; |
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} |
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/*
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* search_plan_tree |
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* |
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* Search through a PlanState tree for a scan node on the specified table. |
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* Return NULL if not found or multiple candidates. |
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*/ |
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static ScanState * |
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search_plan_tree(PlanState *node, Oid table_oid) |
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{ |
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if (node == NULL) |
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return NULL; |
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switch (nodeTag(node)) |
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{ |
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/*
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* scan nodes can all be treated alike |
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*/ |
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case T_SeqScanState: |
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case T_IndexScanState: |
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case T_BitmapHeapScanState: |
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case T_TidScanState: |
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{ |
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ScanState *sstate = (ScanState *) node; |
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if (RelationGetRelid(sstate->ss_currentRelation) == table_oid) |
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return sstate; |
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break; |
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} |
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/*
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* For Append, we must look through the members; watch out for |
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* multiple matches (possible if it was from UNION ALL) |
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*/ |
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case T_AppendState: |
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{ |
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AppendState *astate = (AppendState *) node; |
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ScanState *result = NULL; |
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int i; |
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for (i = 0; i < astate->as_nplans; i++) |
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{ |
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ScanState *elem = search_plan_tree(astate->appendplans[i], |
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table_oid); |
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if (!elem) |
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continue; |
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if (result) |
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return NULL; /* multiple matches */ |
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result = elem; |
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} |
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return result; |
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} |
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/*
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* Result and Limit can be descended through (these are safe |
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* because they always return their input's current row) |
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*/ |
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case T_ResultState: |
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case T_LimitState: |
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return search_plan_tree(node->lefttree, table_oid); |
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/*
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* SubqueryScan too, but it keeps the child in a different place |
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*/ |
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case T_SubqueryScanState: |
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return search_plan_tree(((SubqueryScanState *) node)->subplan, |
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table_oid); |
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default: |
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/* Otherwise, assume we can't descend through it */ |
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break; |
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} |
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return NULL; |
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} |
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