sql/catalog: eliminate repeated database descriptor lookups

Previously, one code path of `ResolveExisting` would repeatedly lookup the
same database descriptor for each schema in the search path. The
`pg_catalog` and `pg_extension` schemas are implicitly included
in the search path, so in the common case where the search path is the
default value of `"$user", public`, there were four lookups for the same
database descriptor.

This commit performs the database descriptor lookup once and reuses it
for looking up objects in each schema of the search path.

Release note: None

pkg/bench/rttanalysis/testdata/benchmark_expectations

@@ -119,12 +119,12 @@ exp,benchmark
 1,SystemDatabaseQueries/select_system.users_with_empty_database_Name
 1,SystemDatabaseQueries/select_system.users_with_schema_Name
 1,SystemDatabaseQueries/select_system.users_without_schema_Name
-20,Truncate/truncate_1_column_0_rows
-20,Truncate/truncate_1_column_1_row
-20,Truncate/truncate_1_column_2_rows
-20,Truncate/truncate_2_column_0_rows
-20,Truncate/truncate_2_column_1_rows
-20,Truncate/truncate_2_column_2_rows
+18,Truncate/truncate_1_column_0_rows
+18,Truncate/truncate_1_column_1_row
+18,Truncate/truncate_1_column_2_rows
+18,Truncate/truncate_2_column_0_rows
+18,Truncate/truncate_2_column_1_rows
+18,Truncate/truncate_2_column_2_rows
 3,UDFResolution/select_from_udf
 5,UseManyRoles/use_2_roles
 3,UseManyRoles/use_50_roles

pkg/ccl/benchccl/rttanalysisccl/testdata/benchmark_expectations

@@ -11,9 +11,9 @@ exp,benchmark
 14,AlterSurvivalGoals/alter_empty_database_from_zone_to_region
 24,AlterSurvivalGoals/alter_populated_database_from_region_to_zone
 24,AlterSurvivalGoals/alter_populated_database_from_zone_to_region
-25,AlterTableLocality/alter_from_global_to_rbr
-16,AlterTableLocality/alter_from_global_to_regional_by_table
-13,AlterTableLocality/alter_from_rbr_to_global
-13,AlterTableLocality/alter_from_rbr_to_regional_by_table
-16,AlterTableLocality/alter_from_regional_by_table_to_global
-25,AlterTableLocality/alter_from_regional_by_table_to_rbr
+28,AlterTableLocality/alter_from_global_to_rbr
+19,AlterTableLocality/alter_from_global_to_regional_by_table
+18,AlterTableLocality/alter_from_rbr_to_global
+18,AlterTableLocality/alter_from_rbr_to_regional_by_table
+19,AlterTableLocality/alter_from_regional_by_table_to_global
+28,AlterTableLocality/alter_from_regional_by_table_to_rbr

pkg/sql/catalog/resolver/resolver.go

@@ -378,26 +378,29 @@ func ResolveExisting(
 		return found, prefix, result, err
 	}
 
+	db, err := r.LookupDatabase(ctx, curDb)
+	if err != nil {
+		return false, prefix, nil, err
+	}
+	if curDb != "" && db == nil {
+		// If we have a database, and we didn't find it, then we're never going
+		// to find it because it must not exist. This error return path is a bit
+		// of a rough edge, but it preserves backwards compatibility and makes
+		// sure we return a database does not exist error in cases where the
+		// current database definitely does not exist.
+		return false, prefix, nil, sqlerrors.NewUndefinedDatabaseError(curDb)
+	}
+
 	// This is a naked object name. Use the search path.
 	iter := searchPath.Iter()
-	foundDatabase := false
 	for next, ok := iter.Next(); ok; next, ok = iter.Next() {
-		if found, prefix, result, err = r.LookupObject(
-			ctx, lookupFlags, curDb, next, u.Object(),
+		if found, prefix, result, err = r.LookupObjectInDatabase(
+			ctx, lookupFlags, db, next, u.Object(),
 		); found || err != nil {
 			return found, prefix, result, err
 		}
-		foundDatabase = foundDatabase || prefix.Database != nil
 	}
 
-	// If we have a database, and we didn't find it, then we're never going to
-	// find it because it must not exist. This error return path is a bit of
-	// a rough edge, but it preserves backwards compatibility and makes sure
-	// we return a database does not exist error in cases where the current
-	// database definitely does not exist.
-	if curDb != "" && !foundDatabase {
-		return false, prefix, nil, sqlerrors.NewUndefinedDatabaseError(curDb)
-	}
 	return false, prefix, nil, nil
 }