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Diffstat (limited to 'src/backend/executor/execCurrent.c')
| -rw-r--r-- | src/backend/executor/execCurrent.c | 426 |
1 files changed, 426 insertions, 0 deletions
diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c new file mode 100644 index 0000000..b34b180 --- /dev/null +++ b/src/backend/executor/execCurrent.c @@ -0,0 +1,426 @@ +/*------------------------------------------------------------------------- + * + * execCurrent.c + * executor support for WHERE CURRENT OF cursor + * + * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/backend/executor/execCurrent.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include "access/genam.h" +#include "access/relscan.h" +#include "access/sysattr.h" +#include "catalog/pg_type.h" +#include "executor/executor.h" +#include "utils/builtins.h" +#include "utils/lsyscache.h" +#include "utils/portal.h" +#include "utils/rel.h" + + +static char *fetch_cursor_param_value(ExprContext *econtext, int paramId); +static ScanState *search_plan_tree(PlanState *node, Oid table_oid, + bool *pending_rescan); + + +/* + * execCurrentOf + * + * Given a CURRENT OF expression and the OID of a table, determine which row + * of the table is currently being scanned by the cursor named by CURRENT OF, + * and return the row's TID into *current_tid. + * + * Returns true if a row was identified. Returns false if the cursor is valid + * for the table but is not currently scanning a row of the table (this is a + * legal situation in inheritance cases). Raises error if cursor is not a + * valid updatable scan of the specified table. + */ +bool +execCurrentOf(CurrentOfExpr *cexpr, + ExprContext *econtext, + Oid table_oid, + ItemPointer current_tid) +{ + char *cursor_name; + char *table_name; + Portal portal; + QueryDesc *queryDesc; + + /* Get the cursor name --- may have to look up a parameter reference */ + if (cexpr->cursor_name) + cursor_name = cexpr->cursor_name; + else + cursor_name = fetch_cursor_param_value(econtext, cexpr->cursor_param); + + /* Fetch table name for possible use in error messages */ + table_name = get_rel_name(table_oid); + if (table_name == NULL) + elog(ERROR, "cache lookup failed for relation %u", table_oid); + + /* Find the cursor's portal */ + portal = GetPortalByName(cursor_name); + if (!PortalIsValid(portal)) + ereport(ERROR, + (errcode(ERRCODE_UNDEFINED_CURSOR), + errmsg("cursor \"%s\" does not exist", cursor_name))); + + /* + * We have to watch out for non-SELECT queries as well as held cursors, + * both of which may have null queryDesc. + */ + if (portal->strategy != PORTAL_ONE_SELECT) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a SELECT query", + cursor_name))); + queryDesc = portal->queryDesc; + if (queryDesc == NULL || queryDesc->estate == NULL) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is held from a previous transaction", + cursor_name))); + + /* + * We have two different strategies depending on whether the cursor uses + * FOR UPDATE/SHARE or not. The reason for supporting both is that the + * FOR UPDATE code is able to identify a target table in many cases where + * the other code can't, while the non-FOR-UPDATE case allows use of WHERE + * CURRENT OF with an insensitive cursor. + */ + if (queryDesc->estate->es_rowmarks) + { + ExecRowMark *erm; + Index i; + + /* + * Here, the query must have exactly one FOR UPDATE/SHARE reference to + * the target table, and we dig the ctid info out of that. + */ + erm = NULL; + for (i = 0; i < queryDesc->estate->es_range_table_size; i++) + { + ExecRowMark *thiserm = queryDesc->estate->es_rowmarks[i]; + + if (thiserm == NULL || + !RowMarkRequiresRowShareLock(thiserm->markType)) + continue; /* ignore non-FOR UPDATE/SHARE items */ + + if (thiserm->relid == table_oid) + { + if (erm) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" has multiple FOR UPDATE/SHARE references to table \"%s\"", + cursor_name, table_name))); + erm = thiserm; + } + } + + if (erm == NULL) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" does not have a FOR UPDATE/SHARE reference to table \"%s\"", + cursor_name, table_name))); + + /* + * The cursor must have a current result row: per the SQL spec, it's + * an error if not. + */ + if (portal->atStart || portal->atEnd) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not positioned on a row", + cursor_name))); + + /* Return the currently scanned TID, if there is one */ + if (ItemPointerIsValid(&(erm->curCtid))) + { + *current_tid = erm->curCtid; + return true; + } + + /* + * This table didn't produce the cursor's current row; some other + * inheritance child of the same parent must have. Signal caller to + * do nothing on this table. + */ + return false; + } + else + { + /* + * Without FOR UPDATE, we dig through the cursor's plan to find the + * scan node. Fail if it's not there or buried underneath + * aggregation. + */ + ScanState *scanstate; + bool pending_rescan = false; + + scanstate = search_plan_tree(queryDesc->planstate, table_oid, + &pending_rescan); + if (!scanstate) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", + cursor_name, table_name))); + + /* + * The cursor must have a current result row: per the SQL spec, it's + * an error if not. We test this at the top level, rather than at the + * scan node level, because in inheritance cases any one table scan + * could easily not be on a row. We want to return false, not raise + * error, if the passed-in table OID is for one of the inactive scans. + */ + if (portal->atStart || portal->atEnd) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not positioned on a row", + cursor_name))); + + /* + * Now OK to return false if we found an inactive scan. It is + * inactive either if it's not positioned on a row, or there's a + * rescan pending for it. + */ + if (TupIsNull(scanstate->ss_ScanTupleSlot) || pending_rescan) + return false; + + /* + * Extract TID of the scan's current row. The mechanism for this is + * in principle scan-type-dependent, but for most scan types, we can + * just dig the TID out of the physical scan tuple. + */ + if (IsA(scanstate, IndexOnlyScanState)) + { + /* + * For IndexOnlyScan, the tuple stored in ss_ScanTupleSlot may be + * a virtual tuple that does not have the ctid column, so we have + * to get the TID from xs_ctup.t_self. + */ + IndexScanDesc scan = ((IndexOnlyScanState *) scanstate)->ioss_ScanDesc; + + *current_tid = scan->xs_heaptid; + } + else + { + /* + * Default case: try to fetch TID from the scan node's current + * tuple. As an extra cross-check, verify tableoid in the current + * tuple. If the scan hasn't provided a physical tuple, we have + * to fail. + */ + Datum ldatum; + bool lisnull; + ItemPointer tuple_tid; + +#ifdef USE_ASSERT_CHECKING + ldatum = slot_getsysattr(scanstate->ss_ScanTupleSlot, + TableOidAttributeNumber, + &lisnull); + if (lisnull) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", + cursor_name, table_name))); + Assert(DatumGetObjectId(ldatum) == table_oid); +#endif + + ldatum = slot_getsysattr(scanstate->ss_ScanTupleSlot, + SelfItemPointerAttributeNumber, + &lisnull); + if (lisnull) + ereport(ERROR, + (errcode(ERRCODE_INVALID_CURSOR_STATE), + errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"", + cursor_name, table_name))); + tuple_tid = (ItemPointer) DatumGetPointer(ldatum); + + *current_tid = *tuple_tid; + } + + Assert(ItemPointerIsValid(current_tid)); + + return true; + } +} + +/* + * fetch_cursor_param_value + * + * Fetch the string value of a param, verifying it is of type REFCURSOR. + */ +static char * +fetch_cursor_param_value(ExprContext *econtext, int paramId) +{ + ParamListInfo paramInfo = econtext->ecxt_param_list_info; + + if (paramInfo && + paramId > 0 && paramId <= paramInfo->numParams) + { + ParamExternData *prm; + ParamExternData prmdata; + + /* give hook a chance in case parameter is dynamic */ + if (paramInfo->paramFetch != NULL) + prm = paramInfo->paramFetch(paramInfo, paramId, false, &prmdata); + else + prm = ¶mInfo->params[paramId - 1]; + + if (OidIsValid(prm->ptype) && !prm->isnull) + { + /* safety check in case hook did something unexpected */ + if (prm->ptype != REFCURSOROID) + ereport(ERROR, + (errcode(ERRCODE_DATATYPE_MISMATCH), + errmsg("type of parameter %d (%s) does not match that when preparing the plan (%s)", + paramId, + format_type_be(prm->ptype), + format_type_be(REFCURSOROID)))); + + /* We know that refcursor uses text's I/O routines */ + return TextDatumGetCString(prm->value); + } + } + + ereport(ERROR, + (errcode(ERRCODE_UNDEFINED_OBJECT), + errmsg("no value found for parameter %d", paramId))); + return NULL; +} + +/* + * search_plan_tree + * + * Search through a PlanState tree for a scan node on the specified table. + * Return NULL if not found or multiple candidates. + * + * CAUTION: this function is not charged simply with finding some candidate + * scan, but with ensuring that that scan returned the plan tree's current + * output row. That's why we must reject multiple-match cases. + * + * If a candidate is found, set *pending_rescan to true if that candidate + * or any node above it has a pending rescan action, i.e. chgParam != NULL. + * That indicates that we shouldn't consider the node to be positioned on a + * valid tuple, even if its own state would indicate that it is. (Caller + * must initialize *pending_rescan to false, and should not trust its state + * if multiple candidates are found.) + */ +static ScanState * +search_plan_tree(PlanState *node, Oid table_oid, + bool *pending_rescan) +{ + ScanState *result = NULL; + + if (node == NULL) + return NULL; + switch (nodeTag(node)) + { + /* + * Relation scan nodes can all be treated alike: check to see if + * they are scanning the specified table. + * + * ForeignScan and CustomScan might not have a currentRelation, in + * which case we just ignore them. (We dare not descend to any + * child plan nodes they might have, since we do not know the + * relationship of such a node's current output tuple to the + * children's current outputs.) + */ + case T_SeqScanState: + case T_SampleScanState: + case T_IndexScanState: + case T_IndexOnlyScanState: + case T_BitmapHeapScanState: + case T_TidScanState: + case T_TidRangeScanState: + case T_ForeignScanState: + case T_CustomScanState: + { + ScanState *sstate = (ScanState *) node; + + if (sstate->ss_currentRelation && + RelationGetRelid(sstate->ss_currentRelation) == table_oid) + result = sstate; + break; + } + + /* + * For Append, we can check each input node. It is safe to + * descend to the inputs because only the input that resulted in + * the Append's current output node could be positioned on a tuple + * at all; the other inputs are either at EOF or not yet started. + * Hence, if the desired table is scanned by some + * currently-inactive input node, we will find that node but then + * our caller will realize that it didn't emit the tuple of + * interest. + * + * We do need to watch out for multiple matches (possible if + * Append was from UNION ALL rather than an inheritance tree). + * + * Note: we can NOT descend through MergeAppend similarly, since + * its inputs are likely all active, and we don't know which one + * returned the current output tuple. (Perhaps that could be + * fixed if we were to let this code know more about MergeAppend's + * internal state, but it does not seem worth the trouble. Users + * should not expect plans for ORDER BY queries to be considered + * simply-updatable, since they won't be if the sorting is + * implemented by a Sort node.) + */ + case T_AppendState: + { + AppendState *astate = (AppendState *) node; + int i; + + for (i = 0; i < astate->as_nplans; i++) + { + ScanState *elem = search_plan_tree(astate->appendplans[i], + table_oid, + pending_rescan); + + if (!elem) + continue; + if (result) + return NULL; /* multiple matches */ + result = elem; + } + break; + } + + /* + * Result and Limit can be descended through (these are safe + * because they always return their input's current row) + */ + case T_ResultState: + case T_LimitState: + result = search_plan_tree(node->lefttree, + table_oid, + pending_rescan); + break; + + /* + * SubqueryScan too, but it keeps the child in a different place + */ + case T_SubqueryScanState: + result = search_plan_tree(((SubqueryScanState *) node)->subplan, + table_oid, + pending_rescan); + break; + + default: + /* Otherwise, assume we can't descend through it */ + break; + } + + /* + * If we found a candidate at or below this node, then this node's + * chgParam indicates a pending rescan that will affect the candidate. + */ + if (result && node->chgParam != NULL) + *pending_rescan = true; + + return result; +} |