execbuilder: use lookup join lookup table distribution in home region checking

This commit updates enforce_home_region checking to build the lookup
join lookup table's distribution the same as is done in the coster.
This can prevent some lookup joins with a home region from being
errored out as not having a home region.

Informs: cockroachdb#105942

Release note: None

Author: Mark Sirek

pkg/ccl/logictestccl/testdata/logic_test/multi_region_remote_access_error

@@ -246,6 +246,9 @@ CREATE TABLE customers (
     name   STRING NOT NULL
 ) LOCALITY REGIONAL BY ROW;
 
+statement ok
+INSERT INTO customers VALUES ('69a1c2c2-5b18-459e-94d2-079dc53a4dd0', 'ACME Sprockets')
+
 statement ok
 ALTER TABLE customers INJECT STATISTICS '[
   {
@@ -277,6 +280,9 @@ CREATE TABLE orders (
     FOREIGN KEY (cust_id, crdb_region) REFERENCES customers (id, crdb_region) ON UPDATE CASCADE
 ) LOCALITY REGIONAL BY ROW;
 
+statement ok
+INSERT INTO orders VALUES ('69a1c2c2-5b18-459e-94d2-079dc53a4dd0', '69a1c2c2-5b18-459e-94d2-079dc53a4dd0', 'Super Deluxe Sprocket')
+
 statement ok
 ALTER TABLE orders INJECT STATISTICS '[
   {
@@ -636,11 +642,33 @@ locality-optimized-search
       ├── constraint: /11/10: [/'ca-central-1' - /'us-east-1']
       └── limit: 1
 
-# Locality optimized search with lookup join will be supported in phase 2 or 3
-# when we can dynamically determine if the lookup will access a remote region.
-retry
+# Static checking should not error this query out, because we now generate a
+# plan with a home region for it.
+query T retry
+EXPLAIN (OPT) SELECT * FROM customers c JOIN orders o ON c.id = o.cust_id AND
+  (c.crdb_region = o.crdb_region) WHERE c.id = '69a1c2c2-5b18-459e-94d2-079dc53a4dd0'
+----
+project
+ └── inner-join (lookup orders [as=o])
+      ├── lookup columns are key
+      ├── inner-join (lookup orders@orders_cust_id_idx [as=o])
+      │    ├── locality-optimized-search
+      │    │    ├── scan customers [as=c]
+      │    │    │    └── constraint: /15/13: [/'ap-southeast-2'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0' - /'ap-southeast-2'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0']
+      │    │    └── scan customers [as=c]
+      │    │         └── constraint: /20/18
+      │    │              ├── [/'ca-central-1'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0' - /'ca-central-1'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0']
+      │    │              └── [/'us-east-1'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0' - /'us-east-1'/'69a1c2c2-5b18-459e-94d2-079dc53a4dd0']
+      │    └── filters
+      │         └── cust_id = '69a1c2c2-5b18-459e-94d2-079dc53a4dd0'
+      └── filters (true)
+
+# This query should error out dynamically during execution, but
+# `GetLookupJoinLookupTableDistribution` doesn't currently work in
+# the execbuilder phase because `Optimizer.stateMap` is empty.
+# TODO(msirek): Fix this test case to not error out statically.
 statement error pq: Query has no home region\. Try adding a filter on o\.crdb_region and/or on key column \(o\.cust_id\)\. For more information, see https://www.cockroachlabs.com/docs/stable/cost-based-optimizer.html#control-whether-queries-are-limited-to-a-single-region
-SELECT * FROM customers c JOIN orders o ON c.id = o.cust_id AND
+SELECT 'a' FROM customers c JOIN orders o ON c.id = o.cust_id AND
   (c.crdb_region = o.crdb_region) WHERE c.id = '69a1c2c2-5b18-459e-94d2-079dc53a4dd0'
 
 # Locality optimized lookup join is allowed.

pkg/sql/opt/exec/execbuilder/relational.go

@@ -2311,7 +2311,8 @@ func (b *Builder) handleRemoteLookupJoinError(join *memo.LookupJoinExpr) (err er
 	if lookupTable.IsGlobalTable() || join.LocalityOptimized || join.ChildOfLocalityOptimizedSearch {
 		// HomeRegion() does not automatically fill in the home region of a global
 		// table as the gateway region, so let's manually set it here.
-		// Locality optimized joins are considered local in phase 1.
+		// Locality optimized joins are considered local for static
+		// enforce_home_region checks.
 		homeRegion = gatewayRegion
 	} else {
 		homeRegion, _ = lookupTable.HomeRegion()
@@ -2343,7 +2344,19 @@ func (b *Builder) handleRemoteLookupJoinError(join *memo.LookupJoinExpr) (err er
 			}
 		}
 	}
-
+	// If the specialized methods of setting the home region above don't succeed,
+	// see if `GetLookupJoinLookupTableDistribution` can find the lookup table's
+	// distribution.
+	// TODO(msirek): Check if the specialized methods above are even needed any
+	// more.
+	if homeRegion == "" && b.optimizer != nil && b.optimizer.Coster() != nil {
+		_, physicalDistribution := distribution.BuildLookupJoinLookupTableDistribution(
+			b.ctx, b.evalCtx, join, join.RequiredPhysical(), b.optimizer.MaybeGetBestCostRelation,
+		)
+		if len(physicalDistribution.Regions) == 1 {
+			homeRegion = physicalDistribution.Regions[0]
+		}
+	}
 	if homeRegion != "" {
 		if foundLocalRegion {
 			if queryHasHomeRegion {