greenplumn execCurrent 源码
greenplumn execCurrent 代码
文件路径：/src/backend/executor/execCurrent.c
/*-------------------------------------------------------------------------
*
* execCurrent.c
* executor support for WHERE CURRENT OF cursor
*
* Portions Copyright (c) 1996-2019, 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"
#include "access/table.h"
#include "parser/parse_relation.h"
#include "parser/parsetree.h"
#include "cdb/cdbvars.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.
*
* In GPDB, we also check that the tuple came from the current segment.
*/
bool
execCurrentOf(CurrentOfExpr *cexpr,
ExprContext *econtext,
Oid table_oid,
ItemPointer current_tid)
{
int current_gp_segment_id = -1;
Oid current_table_oid;
/*
* In an executor node, the dispatcher should've included the current
* position of the cursor along with the query plan. Find and return it
* from there.
*/
if (Gp_role == GP_ROLE_EXECUTE)
{
ListCell *lc;
char *cursor_name;
bool found = false;
/* 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);
foreach (lc, econtext->ecxt_estate->es_cursorPositions)
{
CursorPosInfo *cpos = (CursorPosInfo *) lfirst(lc);
if (strcmp(cpos->cursor_name, cursor_name) == 0)
{
current_gp_segment_id = cpos->gp_segment_id;
current_table_oid = cpos->table_oid;
ItemPointerCopy(&cpos->ctid, current_tid);
found = true;
break;
}
}
/* Not found. Odd, the dispatcher should've checked for this already. */
if (!found)
elog(ERROR, "no cursor position information found for cursor \"%s\"",
cursor_name);
}
else
{
getCurrentOf(cexpr, econtext, table_oid, current_tid,
¤t_gp_segment_id, ¤t_table_oid, NULL);
}
/*
* Found the cursor. Does the table and segment match?
*/
if (current_gp_segment_id == GpIdentity.segindex &&
(current_table_oid == InvalidOid || current_table_oid == table_oid))
{
return true;
}
else
return false;
}
/*
* Return the current position of a cursor that a CURRENT OF expression
* refers to.
*
* This checks that the cursor is valid for table specified by 'table_oid',
* but it doesn't have to be scanning a row of that table (i.e. it can
* be scanning a row of a different table in the same inheritance hierarchy).
* The current table's oid is returned in *current_table_oid.
*
* GPDB calls it before dispatching to make QEs get the same current position
* of the cursor.
*/
void
getCurrentOf(CurrentOfExpr *cexpr,
ExprContext *econtext,
Oid table_oid,
ItemPointer current_tid,
int *current_gp_segment_id,
Oid *current_table_oid,
char **p_cursor_name)
{
char *cursor_name;
char *table_name;
Portal portal;
QueryDesc *queryDesc;
TupleTableSlot *slot;
AttrNumber gp_segment_id_attno;
AttrNumber ctid_attno;
AttrNumber tableoid_attno;
bool isnull;
Datum value;
/*
* In an executor node, execCurrentOf() is supposed to use the cursor
* position information received from the dispatcher, and we shouldn't
* get here.
*/
if (Gp_role == GP_ROLE_EXECUTE)
elog(ERROR, "getCurrentOf called in executor node");
/* Get the cursor name --- may have to look up a parameter reference */
if (cexpr->cursor_name)
cursor_name = cexpr->cursor_name;
else
{
if (!econtext->ecxt_param_list_info)
elog(ERROR, "no cursor name information found");
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)));
/*
* The referenced cursor must be simply updatable. This has already
* been discerned by parse/analyze for the DECLARE CURSOR of the given
* cursor. This flag assures us that gp_segment_id, ctid, and tableoid (if necessary)
* will be available as junk metadata, courtesy of preprocess_targetlist.
*
* Apply simply updatable check to ordinary tables. Refer to the issue:
* https://github.com/greenplum-db/gpdb/issues/9838.
*/
if (!OidIsValid(queryDesc->plannedstmt->simplyUpdatableRel))
ereport(ERROR,
(errcode(ERRCODE_INVALID_CURSOR_STATE),
errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"",
cursor_name, table_name)));
/*
* gpdb partition table routine is different with upstream
* so we hold private updatable check method.
*/
/* better hold a lock already since we're scanning it */
Relation rel = table_open(table_oid, NoLock);
char relkind = rel->rd_rel->relkind;
bool relispartition = rel->rd_rel->relispartition;
table_close(rel, NoLock);
if (relkind == RELKIND_PARTITIONED_TABLE ||
relispartition ||
get_rel_persistence(table_oid) == RELPERSISTENCE_TEMP)
{
/*
* The target relation must directly match the cursor's relation. This throws out
* the simple case in which a cursor is declared against table X and the update is
* issued against Y. Moreover, this disallows some subtler inheritance cases where
* Y inherits from X. While such cases could be implemented, it seems wiser to
* simply error out cleanly.
*/
if (table_oid != queryDesc->plannedstmt->simplyUpdatableRel)
ereport(ERROR,
(errcode(ERRCODE_INVALID_CURSOR_STATE),
errmsg("cursor \"%s\" is not a simply updatable scan of table \"%s\"",
cursor_name, table_name)));
}
else
{
ScanState *scanstate;
bool pending_rescan = false;
/*
* 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 = 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)));
/*
* 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.
*
* GPDB: Neither of those methods work in GPDB, however, because the scan
* is most likely below a Motion node, and belongs to a different slice
* than the top node. The slot of the scan node is empty, and the tuple
* has been received by a Motion node higher up in the tree instead. So
* we use a different approach.
*/
#if 0
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;
}
#endif
{
/*
* GPDB method:
*
* The planner should've made the gp_segment_id, ctid, and tableoid
* available as junk columns at the top of the plan. To retrieve this
* junk metadata, we leverage the EState's junkfilter against the raw
* tuple yielded by the top node in the plan.
*/
slot = queryDesc->planstate->ps_ResultTupleSlot;
if (TupIsNull(slot))
elog(ERROR, "TupleTableslot is empty");
Assert(queryDesc->estate->es_junkFilter);
/* extract gp_segment_id metadata */
gp_segment_id_attno = ExecFindJunkAttribute(queryDesc->estate->es_junkFilter, "gp_segment_id");
if (!AttributeNumberIsValid(gp_segment_id_attno))
elog(ERROR, "could not find junk gp_segment_id column");
value = ExecGetJunkAttribute(slot, gp_segment_id_attno, &isnull);
if (isnull)
elog(ERROR, "gp_segment_id is NULL");
*current_gp_segment_id = DatumGetInt32(value);
/* extract ctid metadata */
ctid_attno = ExecFindJunkAttribute(queryDesc->estate->es_junkFilter, "ctid");
if (!AttributeNumberIsValid(ctid_attno))
elog(ERROR, "could not find junk ctid column");
value = ExecGetJunkAttribute(slot, ctid_attno, &isnull);
if (isnull)
elog(ERROR, "ctid is NULL");
ItemPointerCopy(DatumGetItemPointer(value), current_tid);
/*
* extract tableoid metadata
*
* DECLARE CURSOR planning only includes tableoid metadata when
* scrolling a partitioned table. Otherwise gp_segment_id and ctid alone
* are sufficient to uniquely identify a tuple.
*/
tableoid_attno = ExecFindJunkAttribute(queryDesc->estate->es_junkFilter,
"tableoid");
if (AttributeNumberIsValid(tableoid_attno))
{
value = ExecGetJunkAttribute(slot, tableoid_attno, &isnull);
if (isnull)
elog(ERROR, "tableoid is NULL");
*current_table_oid = DatumGetObjectId(value);
/*
* This is our last opportunity to verify that the physical table given
* by tableoid is, indeed, simply updatable.
*/
(void) isSimplyUpdatableRelation(*current_table_oid, false /* noerror */);
}
if (p_cursor_name)
*p_cursor_name = pstrdup(cursor_name);
}
}
/*
* 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.
*
* 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
*/
case T_SeqScanState:
case T_SampleScanState:
case T_IndexScanState:
case T_IndexOnlyScanState:
case T_BitmapHeapScanState:
case T_TidScanState:
case T_ForeignScanState:
case T_CustomScanState:
{
ScanState *sstate = (ScanState *) node;
if (RelationGetRelid(sstate->ss_currentRelation) == table_oid)
result = sstate;
break;
}
/*
* For Append, we must look through the members; watch out for
* multiple matches (possible if it was from UNION ALL)
*/
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;
}
/*
* Similarly for MergeAppend
*/
case T_MergeAppendState:
{
MergeAppendState *mstate = (MergeAppendState *) node;
int i;
for (i = 0; i < mstate->ms_nplans; i++)
{
ScanState *elem = search_plan_tree(mstate->mergeplans[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;
case T_MotionState:
result = search_plan_tree(node->lefttree, 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;
}
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