kv: deflake TestFollowerReadsWithStaleDescriptor

Fixes cockroachdb#108087.

This fix avoids a data race in the test. The race was harmless, but
could cause the test to fail when run with the race detector.

Release note: None

Author: nvb

pkg/ccl/kvccl/kvfollowerreadsccl/followerreads_test.go

@@ -14,6 +14,7 @@ import (
 	"fmt"
 	"math"
 	"strings"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -697,7 +698,8 @@ func TestFollowerReadsWithStaleDescriptor(t *testing.T) {
 	// The test uses follower_read_timestamp().
 	defer utilccl.TestingEnableEnterprise()()
 
-	historicalQuery := `SELECT * FROM test AS OF SYSTEM TIME follower_read_timestamp() WHERE k=2`
+	var historicalQuery atomic.Value
+	historicalQuery.Store(`SELECT * FROM test AS OF SYSTEM TIME follower_read_timestamp() WHERE k=2`)
 	recCh := make(chan tracingpb.Recording, 1)
 
 	tc := testcluster.StartTestCluster(t, 4,
@@ -732,7 +734,7 @@ func TestFollowerReadsWithStaleDescriptor(t *testing.T) {
 						},
 						SQLExecutor: &sql.ExecutorTestingKnobs{
 							WithStatementTrace: func(trace tracingpb.Recording, stmt string) {
-								if stmt == historicalQuery {
+								if stmt == historicalQuery.Load().(string) {
 									recCh <- trace
 								}
 							},
@@ -786,7 +788,7 @@ func TestFollowerReadsWithStaleDescriptor(t *testing.T) {
 	// not be executed as a follower read since it attempts to use n2 which
 	// doesn't have a replica any more and then it tries n1 which returns an
 	// updated descriptor.
-	n4.Exec(t, historicalQuery)
+	n4.Exec(t, historicalQuery.Load().(string))
 	// As a sanity check, verify that this was not a follower read.
 	rec := <-recCh
 	require.False(t, kv.OnlyFollowerReads(rec), "query was served through follower reads: %s", rec)
@@ -812,7 +814,7 @@ func TestFollowerReadsWithStaleDescriptor(t *testing.T) {
 	// Run a historical query and assert that it's served from the follower (n3).
 	// n4 should attempt to route to n3 because we pretend n3 has a lower latency
 	// (see testing knob).
-	n4.Exec(t, historicalQuery)
+	n4.Exec(t, historicalQuery.Load().(string))
 	rec = <-recCh
 
 	// Look at the trace and check that we've served a follower read.
@@ -855,8 +857,8 @@ func TestFollowerReadsWithStaleDescriptor(t *testing.T) {
 	// the ReplicaInfo twice for the same range. This allows us to verify that
 	// the cached - in the spanResolverIterator - information is correctly
 	// preserved.
-	historicalQuery = `SELECT * FROM [SELECT * FROM test WHERE k=2 UNION ALL SELECT * FROM test WHERE k=3] AS OF SYSTEM TIME follower_read_timestamp()`
-	n4.Exec(t, historicalQuery)
+	historicalQuery.Store(`SELECT * FROM [SELECT * FROM test WHERE k=2 UNION ALL SELECT * FROM test WHERE k=3] AS OF SYSTEM TIME follower_read_timestamp()`)
+	n4.Exec(t, historicalQuery.Load().(string))
 	rec = <-recCh
 
 	// Sanity check that the plan was distributed.