Add amgettreeheight index AM API routine

The only current implementation is for btree where it calls
_bt_getrootheight().  Other index types can now also use this to pass
information to their amcostestimate routine.  Previously, btree was
hardcoded and other index types could not hook into the optimizer at
this point.

Author: Mark Dilger <mark.dilger@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/E72EAA49-354D-4C2E-8EB9-255197F55330@enterprisedb.com

7 files changed, 21 insertions, 7 deletions

diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c
index 6467bed604a..94a8bd07017 100644
--- a/src/backend/access/brin/brin.c
+++ b/src/backend/access/brin/brin.c
@@ -279,6 +279,7 @@ brinhandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = brinvacuumcleanup;
 	amroutine->amcanreturn = NULL;
 	amroutine->amcostestimate = brincostestimate;
+	amroutine->amgettreeheight = NULL;
 	amroutine->amoptions = brinoptions;
 	amroutine->amproperty = NULL;
 	amroutine->ambuildphasename = NULL;
diff --git a/src/backend/access/gin/ginutil.c b/src/backend/access/gin/ginutil.c
index 5747ae6a4ca..830d67fbc20 100644
--- a/src/backend/access/gin/ginutil.c
+++ b/src/backend/access/gin/ginutil.c
@@ -69,6 +69,7 @@ ginhandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = ginvacuumcleanup;
 	amroutine->amcanreturn = NULL;
 	amroutine->amcostestimate = gincostestimate;
+	amroutine->amgettreeheight = NULL;
 	amroutine->amoptions = ginoptions;
 	amroutine->amproperty = NULL;
 	amroutine->ambuildphasename = NULL;
diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
index ed4ffa63a77..2d7a0687d4a 100644
--- a/src/backend/access/gist/gist.c
+++ b/src/backend/access/gist/gist.c
@@ -91,6 +91,7 @@ gisthandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = gistvacuumcleanup;
 	amroutine->amcanreturn = gistcanreturn;
 	amroutine->amcostestimate = gistcostestimate;
+	amroutine->amgettreeheight = NULL;
 	amroutine->amoptions = gistoptions;
 	amroutine->amproperty = gistproperty;
 	amroutine->ambuildphasename = NULL;
diff --git a/src/backend/access/hash/hash.c b/src/backend/access/hash/hash.c
index 01d06b7c328..a783b9b4e25 100644
--- a/src/backend/access/hash/hash.c
+++ b/src/backend/access/hash/hash.c
@@ -89,6 +89,7 @@ hashhandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = hashvacuumcleanup;
 	amroutine->amcanreturn = NULL;
 	amroutine->amcostestimate = hashcostestimate;
+	amroutine->amgettreeheight = NULL;
 	amroutine->amoptions = hashoptions;
 	amroutine->amproperty = NULL;
 	amroutine->ambuildphasename = NULL;
diff --git a/src/backend/access/nbtree/nbtree.c b/src/backend/access/nbtree/nbtree.c
index 686a3206f72..8cfaab949be 100644
--- a/src/backend/access/nbtree/nbtree.c
+++ b/src/backend/access/nbtree/nbtree.c
@@ -133,6 +133,7 @@ bthandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = btvacuumcleanup;
 	amroutine->amcanreturn = btcanreturn;
 	amroutine->amcostestimate = btcostestimate;
+	amroutine->amgettreeheight = btgettreeheight;
 	amroutine->amoptions = btoptions;
 	amroutine->amproperty = btproperty;
 	amroutine->ambuildphasename = btbuildphasename;
@@ -1445,3 +1446,12 @@ btcanreturn(Relation index, int attno)
 {
 	return true;
 }
+
+/*
+ * btgettreeheight() -- Compute tree height for use by btcostestimate().
+ */
+int
+btgettreeheight(Relation rel)
+{
+	return _bt_getrootheight(rel);
+}
diff --git a/src/backend/access/spgist/spgutils.c b/src/backend/access/spgist/spgutils.c
index 76b80146ff0..72b7661971f 100644
--- a/src/backend/access/spgist/spgutils.c
+++ b/src/backend/access/spgist/spgutils.c
@@ -76,6 +76,7 @@ spghandler(PG_FUNCTION_ARGS)
 	amroutine->amvacuumcleanup = spgvacuumcleanup;
 	amroutine->amcanreturn = spgcanreturn;
 	amroutine->amcostestimate = spgcostestimate;
+	amroutine->amgettreeheight = NULL;
 	amroutine->amoptions = spgoptions;
 	amroutine->amproperty = spgproperty;
 	amroutine->ambuildphasename = NULL;
diff --git a/src/backend/optimizer/util/plancat.c b/src/backend/optimizer/util/plancat.c
index 78a3cfafde4..82f031f4cfe 100644
--- a/src/backend/optimizer/util/plancat.c
+++ b/src/backend/optimizer/util/plancat.c
@@ -241,7 +241,7 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 			Oid			indexoid = lfirst_oid(l);
 			Relation	indexRelation;
 			Form_pg_index index;
-			IndexAmRoutine *amroutine;
+			IndexAmRoutine *amroutine = NULL;
 			IndexOptInfo *info;
 			int			ncolumns,
 						nkeycolumns;
@@ -485,13 +485,12 @@ get_relation_info(PlannerInfo *root, Oid relationObjectId, bool inhparent,
 						info->tuples = rel->tuples;
 				}
 
-				if (info->relam == BTREE_AM_OID)
+				/*
+				 * Get tree height while we have the index open
+				 */
+				if (amroutine->amgettreeheight)
 				{
-					/*
-					 * For btrees, get tree height while we have the index
-					 * open
-					 */
-					info->tree_height = _bt_getrootheight(indexRelation);
+					info->tree_height = amroutine->amgettreeheight(indexRelation);
 				}
 				else
 				{