Create hooks to let a loadable plugin monitor (or even replace) the planner

and/or create plans for hypothetical situations; in particular, investigate
plans that would be generated using hypothetical indexes.  This is a
heavily-rewritten version of the hooks proposed by Gurjeet Singh for his
Index Advisor project.  In this formulation, the index advisor can be
entirely a loadable module instead of requiring a significant part to be
in the core backend, and plans can be generated for hypothetical indexes
without requiring the creation and rolling-back of system catalog entries.

The index advisor patch as-submitted is not compatible with these hooks,
but it needs significant work anyway due to other 8.2-to-8.3 planner
changes.  With these hooks in the core backend, development of the advisor
can proceed as a pgfoundry project.

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index cb95fea77191ecff8f6cbd7cdb20cd4c887dd844..078b1bbc9ee99a20cee11ea17afadcd46bfb5f18 100644 (file)
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -33,6 +33,12 @@
 #include "utils/tuplesort.h"
 
 
+/* Hook for plugins to get control in ExplainOneQuery() */
+ExplainOneQuery_hook_type ExplainOneQuery_hook = NULL;
+/* Hook for plugins to get control in explain_get_index_name() */
+explain_get_index_name_hook_type explain_get_index_name_hook = NULL;
+
+
 typedef struct ExplainState
 {
        /* options */
@@ -61,6 +67,8 @@ static void show_sort_keys(Plan *sortplan, int nkeys, AttrNumber *keycols,
                           StringInfo str, int indent, ExplainState *es);
 static void show_sort_info(SortState *sortstate,
                           StringInfo str, int indent, ExplainState *es);
+static const char *explain_get_index_name(Oid indexId);
+
 
 /*
  * ExplainQuery -
@@ -140,9 +148,6 @@ static void
 ExplainOneQuery(Query *query, ExplainStmt *stmt, const char *queryString,
                                ParamListInfo params, TupOutputState *tstate)
 {
-       PlannedStmt *plan;
-       QueryDesc  *queryDesc;
-
        /* planner will not cope with utility statements */
        if (query->commandType == CMD_UTILITY)
        {
@@ -151,25 +156,19 @@ ExplainOneQuery(Query *query, ExplainStmt *stmt, const char *queryString,
                return;
        }
 
-       /* plan the query */
-       plan = planner(query, 0, params);
-
-       /*
-        * Update snapshot command ID to ensure this query sees results of any
-        * previously executed queries.  (It's a bit cheesy to modify
-        * ActiveSnapshot without making a copy, but for the limited ways in which
-        * EXPLAIN can be invoked, I think it's OK, because the active snapshot
-        * shouldn't be shared with anything else anyway.)
-        */
-       ActiveSnapshot->curcid = GetCurrentCommandId();
+       /* if an advisor plugin is present, let it manage things */
+       if (ExplainOneQuery_hook)
+               (*ExplainOneQuery_hook) (query, stmt, queryString, params, tstate);
+       else
+       {
+               PlannedStmt *plan;
 
-       /* Create a QueryDesc requesting no output */
-       queryDesc = CreateQueryDesc(plan,
-                                                               ActiveSnapshot, InvalidSnapshot,
-                                                               None_Receiver, params,
-                                                               stmt->analyze);
+               /* plan the query */
+               plan = planner(query, 0, params);
 
-       ExplainOnePlan(queryDesc, stmt, tstate);
+               /* run it (if needed) and produce output */
+               ExplainOnePlan(plan, params, stmt, tstate);
+       }
 }
 
 /*
@@ -210,20 +209,35 @@ ExplainOneUtility(Node *utilityStmt, ExplainStmt *stmt,
  * not running the query.  No cursor will be created, however.
  *
  * This is exported because it's called back from prepare.c in the
- * EXPLAIN EXECUTE case
- *
- * Note: the passed-in QueryDesc is freed when we're done with it
+ * EXPLAIN EXECUTE case, and because an index advisor plugin would need
+ * to call it.
  */
 void
-ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
-                          TupOutputState *tstate)
+ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
+                          ExplainStmt *stmt, TupOutputState *tstate)
 {
+       QueryDesc  *queryDesc;
        instr_time      starttime;
        double          totaltime = 0;
        ExplainState *es;
        StringInfoData buf;
        int                     eflags;
 
+       /*
+        * Update snapshot command ID to ensure this query sees results of any
+        * previously executed queries.  (It's a bit cheesy to modify
+        * ActiveSnapshot without making a copy, but for the limited ways in which
+        * EXPLAIN can be invoked, I think it's OK, because the active snapshot
+        * shouldn't be shared with anything else anyway.)
+        */
+       ActiveSnapshot->curcid = GetCurrentCommandId();
+
+       /* Create a QueryDesc requesting no output */
+       queryDesc = CreateQueryDesc(plannedstmt,
+                                                               ActiveSnapshot, InvalidSnapshot,
+                                                               None_Receiver, params,
+                                                               stmt->analyze);
+
        INSTR_TIME_SET_CURRENT(starttime);
 
        /* If analyzing, we need to cope with queued triggers */
@@ -592,7 +606,7 @@ explain_outNode(StringInfo str,
                        if (ScanDirectionIsBackward(((IndexScan *) plan)->indexorderdir))
                                appendStringInfoString(str, " Backward");
                        appendStringInfo(str, " using %s",
-                         quote_identifier(get_rel_name(((IndexScan *) plan)->indexid)));
+                                       explain_get_index_name(((IndexScan *) plan)->indexid));
                        /* FALL THRU */
                case T_SeqScan:
                case T_BitmapHeapScan:
@@ -618,7 +632,7 @@ explain_outNode(StringInfo str,
                        break;
                case T_BitmapIndexScan:
                        appendStringInfo(str, " on %s",
-                                                        quote_identifier(get_rel_name(((BitmapIndexScan *) plan)->indexid)));
+                               explain_get_index_name(((BitmapIndexScan *) plan)->indexid));
                        break;
                case T_SubqueryScan:
                        if (((Scan *) plan)->scanrelid > 0)
@@ -1150,3 +1164,29 @@ show_sort_info(SortState *sortstate,
                pfree(sortinfo);
        }
 }
+
+/*
+ * Fetch the name of an index in an EXPLAIN
+ *
+ * We allow plugins to get control here so that plans involving hypothetical
+ * indexes can be explained.
+ */
+static const char *
+explain_get_index_name(Oid indexId)
+{
+       const char   *result;
+
+       if (explain_get_index_name_hook)
+               result = (*explain_get_index_name_hook) (indexId);
+       else
+               result = NULL;
+       if (result == NULL)
+       {
+               /* default behavior: look in the catalogs and quote it */
+               result = get_rel_name(indexId);
+               if (result == NULL)
+                       elog(ERROR, "cache lookup failed for index %u", indexId);
+               result = quote_identifier(result);
+       }
+       return result;
+}

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index f29e1a1859fe8684078989bf5e4fcd27e7534873..aad8dc05c9c16a5fcfb0e0c78e7d73c94a3ba0e0 100644 (file)
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -678,8 +678,6 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, ExplainStmt *stmt,
 
                if (IsA(pstmt, PlannedStmt))
                {
-                       QueryDesc  *qdesc;
-
                        if (execstmt->into)
                        {
                                if (pstmt->commandType != CMD_SELECT ||
@@ -694,22 +692,7 @@ ExplainExecuteQuery(ExecuteStmt *execstmt, ExplainStmt *stmt,
                                pstmt->intoClause = execstmt->into;
                        }
 
-                       /*
-                        * Update snapshot command ID to ensure this query sees results of
-                        * any previously executed queries.  (It's a bit cheesy to modify
-                        * ActiveSnapshot without making a copy, but for the limited ways
-                        * in which EXPLAIN can be invoked, I think it's OK, because the
-                        * active snapshot shouldn't be shared with anything else anyway.)
-                        */
-                       ActiveSnapshot->curcid = GetCurrentCommandId();
-
-                       /* Create a QueryDesc requesting no output */
-                       qdesc = CreateQueryDesc(pstmt,
-                                                                       ActiveSnapshot, InvalidSnapshot,
-                                                                       None_Receiver,
-                                                                       paramLI, stmt->analyze);
-
-                       ExplainOnePlan(qdesc, stmt, tstate);
+                       ExplainOnePlan(pstmt, paramLI, stmt, tstate);
                }
                else
                {

diff --git a/src/backend/executor/nodeBitmapIndexscan.c b/src/backend/executor/nodeBitmapIndexscan.c
index d0ac90e8197efe8c0d2468bee8ff504775d3f743..87667f72fcc2ecf9dfc07557744bae6274b2f932 100644 (file)
--- a/src/backend/executor/nodeBitmapIndexscan.c
+++ b/src/backend/executor/nodeBitmapIndexscan.c
@@ -198,10 +198,12 @@ ExecEndBitmapIndexScan(BitmapIndexScanState *node)
 #endif
 
        /*
-        * close the index relation
+        * close the index relation (no-op if we didn't open it)
         */
-       index_endscan(indexScanDesc);
-       index_close(indexRelationDesc, NoLock);
+       if (indexScanDesc)
+               index_endscan(indexScanDesc);
+       if (indexRelationDesc)
+               index_close(indexRelationDesc, NoLock);
 }
 
 /* ----------------------------------------------------------------
@@ -256,6 +258,14 @@ ExecInitBitmapIndexScan(BitmapIndexScan *node, EState *estate, int eflags)
        indexstate->ss.ss_currentRelation = NULL;
        indexstate->ss.ss_currentScanDesc = NULL;
 
+       /*
+        * If we are just doing EXPLAIN (ie, aren't going to run the plan),
+        * stop here.  This allows an index-advisor plugin to EXPLAIN a plan
+        * containing references to nonexistent indexes.
+        */
+       if (eflags & EXEC_FLAG_EXPLAIN_ONLY)
+               return indexstate;
+
        /*
         * Open the index relation.
         *

diff --git a/src/backend/executor/nodeIndexscan.c b/src/backend/executor/nodeIndexscan.c
index d4d9aef793bfc16e7285ee309c790de67dcd72eb..e6412a8fec4dfe8042b8dfa9cc619bc450d0802d 100644 (file)
--- a/src/backend/executor/nodeIndexscan.c
+++ b/src/backend/executor/nodeIndexscan.c
@@ -415,10 +415,12 @@ ExecEndIndexScan(IndexScanState *node)
        ExecClearTuple(node->ss.ss_ScanTupleSlot);
 
        /*
-        * close the index relation
+        * close the index relation (no-op if we didn't open it)
         */
-       index_endscan(indexScanDesc);
-       index_close(indexRelationDesc, NoLock);
+       if (indexScanDesc)
+               index_endscan(indexScanDesc);
+       if (indexRelationDesc)
+               index_close(indexRelationDesc, NoLock);
 
        /*
         * close the heap relation.
@@ -520,6 +522,14 @@ ExecInitIndexScan(IndexScan *node, EState *estate, int eflags)
         */
        ExecAssignScanType(&indexstate->ss, RelationGetDescr(currentRelation));
 
+       /*
+        * If we are just doing EXPLAIN (ie, aren't going to run the plan),
+        * stop here.  This allows an index-advisor plugin to EXPLAIN a plan
+        * containing references to nonexistent indexes.
+        */
+       if (eflags & EXEC_FLAG_EXPLAIN_ONLY)
+               return indexstate;
+
        /*
         * Open the index relation.
         *

diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index bb9f468f2b69d426c539689bdcc13357e281c53e..987c113e77c2769b744733bfa44d52f6daf5e78f 100644 (file)
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -42,6 +42,10 @@
 #include "utils/syscache.h"
 
 
+/* Hook for plugins to get control in planner() */
+planner_hook_type planner_hook = NULL;
+
+
 /* Expression kind codes for preprocess_expression */
 #define EXPRKIND_QUAL          0
 #define EXPRKIND_TARGET                1
@@ -79,9 +83,29 @@ static List *postprocess_setop_tlist(List *new_tlist, List *orig_tlist);
  *
  *        Query optimizer entry point
  *
+ * To support loadable plugins that monitor or modify planner behavior,
+ * we provide a hook variable that lets a plugin get control before and
+ * after the standard planning process.  The plugin would normally call
+ * standard_planner().
+ *
+ * Note to plugin authors: standard_planner() scribbles on its Query input,
+ * so you'd better copy that data structure if you want to plan more than once.
+ *
  *****************************************************************************/
 PlannedStmt *
 planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
+{
+       PlannedStmt *result;
+
+       if (planner_hook)
+               result = (*planner_hook) (parse, cursorOptions, boundParams);
+       else
+               result = standard_planner(parse, cursorOptions, boundParams);
+       return result;
+}
+
+PlannedStmt *
+standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 {
        PlannedStmt *result;
        PlannerGlobal *glob;

diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index fd29e537204e1b68f395a7d4c4d55f7acd86a53e..a15b9393f9f79144c82fc3a6c58e8f1851914711 100644 (file)
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -40,6 +40,9 @@
 /* GUC parameter */
 bool           constraint_exclusion = false;
 
+/* Hook for plugins to get control in get_relation_info() */
+get_relation_info_hook_type get_relation_info_hook = NULL;
+
 
 static void estimate_rel_size(Relation rel, int32 *attr_widths,
                                  BlockNumber *pages, double *tuples);
@@ -279,6 +282,14 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
        rel->indexlist = indexinfos;
 
        heap_close(relation, NoLock);
+
+       /*
+        * Allow a plugin to editorialize on the info we obtained from the
+        * catalogs.  Actions might include altering the assumed relation size,
+        * removing an index, or adding a hypothetical index to the indexlist.
+        */
+       if (get_relation_info_hook)
+               (*get_relation_info_hook) (root, relationObjectId, inhparent, rel);
 }
 
 /*

diff --git a/src/include/commands/explain.h b/src/include/commands/explain.h
index 7d882e5b14536817376f5992b2200e3bb5ad8a68..5565380e9b6db71f4f077599277f36e81026a467 100644 (file)
--- a/src/include/commands/explain.h
+++ b/src/include/commands/explain.h
@@ -15,6 +15,18 @@
 
 #include "executor/executor.h"
 
+/* Hook for plugins to get control in ExplainOneQuery() */
+typedef void (*ExplainOneQuery_hook_type) (Query *query,
+                                                                                  ExplainStmt *stmt,
+                                                                                  const char *queryString,
+                                                                                  ParamListInfo params,
+                                                                                  TupOutputState *tstate);
+extern DLLIMPORT ExplainOneQuery_hook_type ExplainOneQuery_hook;
+
+/* Hook for plugins to get control in explain_get_index_name() */
+typedef const char * (*explain_get_index_name_hook_type) (Oid indexId);
+extern DLLIMPORT explain_get_index_name_hook_type explain_get_index_name_hook;
+
 
 extern void ExplainQuery(ExplainStmt *stmt, const char *queryString,
                                                 ParamListInfo params, DestReceiver *dest);
@@ -26,7 +38,7 @@ extern void ExplainOneUtility(Node *utilityStmt, ExplainStmt *stmt,
                                                          ParamListInfo params,
                                                          TupOutputState *tstate);
 
-extern void ExplainOnePlan(QueryDesc *queryDesc, ExplainStmt *stmt,
-                          TupOutputState *tstate);
+extern void ExplainOnePlan(PlannedStmt *plannedstmt, ParamListInfo params,
+                                                  ExplainStmt *stmt, TupOutputState *tstate);
 
 #endif   /* EXPLAIN_H */

diff --git a/src/include/optimizer/plancat.h b/src/include/optimizer/plancat.h
index da3a4cd0ca0478cc90df1ecc3d472d1711ef366f..261f7f5799d220183bde527a3f34b0bdd8459ffa 100644 (file)
--- a/src/include/optimizer/plancat.h
+++ b/src/include/optimizer/plancat.h
@@ -16,6 +16,13 @@
 
 #include "nodes/relation.h"
 
+/* Hook for plugins to get control in get_relation_info() */
+typedef void (*get_relation_info_hook_type) (PlannerInfo *root,
+                                                                                        Oid relationObjectId,
+                                                                                        bool inhparent,
+                                                                                        RelOptInfo *rel);
+extern DLLIMPORT get_relation_info_hook_type get_relation_info_hook;
+
 
 extern void get_relation_info(PlannerInfo *root, Oid relationObjectId,
                                  bool inhparent, RelOptInfo *rel);

diff --git a/src/include/optimizer/planner.h b/src/include/optimizer/planner.h
index c48c596f1bb9fe880d4f473a3aa29b970b47105e..7cfca18a65c35dbfc0cca569533de8a40947b477 100644 (file)
--- a/src/include/optimizer/planner.h
+++ b/src/include/optimizer/planner.h
@@ -18,8 +18,17 @@
 #include "nodes/relation.h"
 
 
+/* Hook for plugins to get control in planner() */
+typedef PlannedStmt * (*planner_hook_type) (Query *parse,
+                                                                                       int cursorOptions,
+                                                                                       ParamListInfo boundParams);
+extern DLLIMPORT planner_hook_type planner_hook;
+
+
 extern PlannedStmt *planner(Query *parse, int cursorOptions,
                ParamListInfo boundParams);
+extern PlannedStmt *standard_planner(Query *parse, int cursorOptions,
+               ParamListInfo boundParams);
 extern Plan *subquery_planner(PlannerGlobal *glob, Query *parse,
                                                          Index level, double tuple_fraction,
                                                          PlannerInfo **subroot);