sql: add cluster setting to enable/disable txn id cache

Resolves #76329

Release note (sql change): new boolean cluster setting
`sql.contention.txn_id_cache.enabled` can be used to turn on/off
transaction ID cache. The default value of this new cluster setting
is `true`.

docs/generated/settings/settings-for-tenants.txt

@@ -77,6 +77,7 @@ server.web_session.purge.max_deletions_per_cycle	integer	10	the maximum number o
 server.web_session.purge.period	duration	1h0m0s	the time until old sessions are deleted
 server.web_session.purge.ttl	duration	1h0m0s	if nonzero, entries in system.web_sessions older than this duration are periodically purged
 server.web_session_timeout	duration	168h0m0s	the duration that a newly created web session will be valid
+sql.contention.txn_id_cache.enabled	boolean	true	whether the txn id cache is enabled
 sql.contention.txn_id_cache.max_size	byte size	64 MiB	the maximum byte size TxnID cache will use
 sql.cross_db_fks.enabled	boolean	false	if true, creating foreign key references across databases is allowed
 sql.cross_db_sequence_owners.enabled	boolean	false	if true, creating sequences owned by tables from other databases is allowed

docs/generated/settings/settings.html

@@ -88,6 +88,7 @@
 <tr><td><code>server.web_session.purge.period</code></td><td>duration</td><td><code>1h0m0s</code></td><td>the time until old sessions are deleted</td></tr>
 <tr><td><code>server.web_session.purge.ttl</code></td><td>duration</td><td><code>1h0m0s</code></td><td>if nonzero, entries in system.web_sessions older than this duration are periodically purged</td></tr>
 <tr><td><code>server.web_session_timeout</code></td><td>duration</td><td><code>168h0m0s</code></td><td>the duration that a newly created web session will be valid</td></tr>
+<tr><td><code>sql.contention.txn_id_cache.enabled</code></td><td>boolean</td><td><code>true</code></td><td>whether the txn id cache is enabled</td></tr>
 <tr><td><code>sql.contention.txn_id_cache.max_size</code></td><td>byte size</td><td><code>64 MiB</code></td><td>the maximum byte size TxnID cache will use</td></tr>
 <tr><td><code>sql.cross_db_fks.enabled</code></td><td>boolean</td><td><code>false</code></td><td>if true, creating foreign key references across databases is allowed</td></tr>
 <tr><td><code>sql.cross_db_sequence_owners.enabled</code></td><td>boolean</td><td><code>false</code></td><td>if true, creating sequences owned by tables from other databases is allowed</td></tr>

pkg/sql/contention/txnidcache/cluster_settings.go

@@ -19,3 +19,11 @@ var MaxSize = settings.RegisterByteSizeSetting(
 	"the maximum byte size TxnID cache will use",
 	64*1024*1024, // 64 MB
 ).WithPublic()
+
+// IsEnabled is used to turn on/off the txn id cache.
+var IsEnabled = settings.RegisterBoolSetting(
+	settings.TenantWritable,
+	"sql.contention.txn_id_cache.enabled",
+	"whether the txn id cache is enabled",
+	true, // defaultValue
+).WithPublic()

pkg/sql/contention/txnidcache/txn_id_cache.go

@@ -145,7 +145,7 @@ func NewTxnIDCache(st *cluster.Settings, metrics *Metrics) *Cache {
 		return MaxSize.Get(&st.SV) / entrySize
 	} /* capacity */)
 
-	t.writer = newWriter(t)
+	t.writer = newWriter(st, t)
 	return t
 }
 

pkg/sql/contention/txnidcache/writer.go

@@ -11,6 +11,7 @@
 package txnidcache
 
 import (
+	"github.com/cockroachdb/cockroach/pkg/settings/cluster"
 	"github.com/cockroachdb/cockroach/pkg/util/encoding"
 	"github.com/cockroachdb/cockroach/pkg/util/uuid"
 )
@@ -20,15 +21,18 @@ import (
 const shardCount = 16
 
 type writer struct {
+	st *cluster.Settings
+
 	shards [shardCount]*concurrentWriteBuffer
 
 	sink messageSink
 }
 
 var _ Writer = &writer{}
 
-func newWriter(sink messageSink) *writer {
+func newWriter(st *cluster.Settings, sink messageSink) *writer {
 	w := &writer{
+		st:   st,
 		sink: sink,
 	}
 
@@ -41,6 +45,9 @@ func newWriter(sink messageSink) *writer {
 
 // Record implements the Writer interface.
 func (w *writer) Record(resolvedTxnID ResolvedTxnID) {
+	if !IsEnabled.Get(&w.st.SV) {
+		return
+	}
 	shardIdx := hashTxnID(resolvedTxnID.TxnID)
 	buffer := w.shards[shardIdx]
 	buffer.Record(resolvedTxnID)

pkg/sql/contention/txnidcache/writer_test.go

@@ -24,6 +24,7 @@ import (
 	"github.com/cockroachdb/cockroach/pkg/util/log"
 	"github.com/cockroachdb/cockroach/pkg/util/stop"
 	"github.com/cockroachdb/cockroach/pkg/util/uuid"
+	"github.com/stretchr/testify/require"
 )
 
 type blackHoleSink struct {
@@ -71,11 +72,12 @@ func BenchmarkWriter(b *testing.B) {
 	defer log.Scope(b).Close(b)
 
 	ctx := context.Background()
+	st := cluster.MakeTestingClusterSettings()
 
 	run := func(b *testing.B, sink messageSink, numOfConcurrentWriter int) {
 		starter := make(chan struct{})
 
-		w := newWriter(sink)
+		w := newWriter(st, sink)
 
 		b.ResetTimer()
 		b.SetBytes(messageBlockSize * entrySize)
@@ -149,3 +151,50 @@ func BenchmarkWriter(b *testing.B) {
 		})
 	}
 }
+
+type counterSink struct {
+	numOfRecord int
+}
+
+var _ messageSink = &counterSink{}
+
+func (c *counterSink) push(block *messageBlock) {
+	for i := 0; i < messageBlockSize; i++ {
+		if !block[i].valid() {
+			break
+		}
+		c.numOfRecord++
+	}
+}
+
+func TestTxnIDCacheCanBeDisabledViaClusterSetting(t *testing.T) {
+	st := cluster.MakeTestingClusterSettings()
+	ctx := context.Background()
+
+	sink := &counterSink{}
+	w := newWriter(st, sink)
+	w.Record(ResolvedTxnID{
+		TxnID: uuid.FastMakeV4(),
+	})
+
+	w.Flush()
+	require.Equal(t, 1, sink.numOfRecord)
+
+	// This should disable txn id cache.
+	IsEnabled.Override(ctx, &st.SV, false)
+
+	w.Record(ResolvedTxnID{
+		TxnID: uuid.FastMakeV4(),
+	})
+	w.Flush()
+	require.Equal(t, 1, sink.numOfRecord)
+
+	// This should re-enable txn id cache.
+	IsEnabled.Override(ctx, &st.SV, true)
+
+	w.Record(ResolvedTxnID{
+		TxnID: uuid.FastMakeV4(),
+	})
+	w.Flush()
+	require.Equal(t, 2, sink.numOfRecord)
+}