backupccl: do not backup merged statistics

Merged statistics are generated from partial statistics and the
related full statistic. Partial statistics are not currently included
in the backup, but will be soon, thus we are excluding merged
statistics from the backup.

Release note: None

pkg/ccl/backupccl/backup_job.go

@@ -423,10 +423,7 @@ func statShouldBeIncludedInBackupRestore(stat *stats.TableStatisticProto) bool {
 	// Forecasts and merged stats are computed from the persisted
 	// stats on demand and do not need to be backed up or
 	// restored.
-	if stat.Name == jobspb.ForecastStatsName || stat.Name == jobspb.MergedStatsName {
-		return false
-	}
-	return true
+	return stat.Name != jobspb.ForecastStatsName && stat.Name != jobspb.MergedStatsName
 }
 
 type backupResumer struct {

pkg/ccl/backupccl/testdata/backup-restore/metadata

@@ -1,16 +1,15 @@
+# This test that we don't back up forecasts or merged statistics.
+#
+# This also serves as a regression test for #86806 -- a bug in which 2
+# or more forecsts would break metadata SST writing.
 new-cluster name=s
 ----
 
-# Make sure that the presence of forecasted stats doesn't break
-# metadata SST writing. This is a regression test for #86806.
-#
-# We create 3 statistics manually which is the minimum needed to
-# create a forecast. Automatic collection is disabled to avoid
-# flakiness.
 exec-sql
 SET CLUSTER SETTING kv.bulkio.write_metadata_sst.enabled = true;
 ----
 
+# Automatic collection is disabled to avoid flakiness.
 exec-sql
 SET CLUSTER SETTING sql.stats.automatic_collection.enabled = false;
 ----
@@ -19,24 +18,58 @@ exec-sql
 CREATE DATABASE db1;
 USE db1;
 CREATE TABLE tab (a INT PRIMARY KEY, b INT);
+INSERT INTO tab VALUES (1, 1), (2, 2), (100, 100);
 ----
 
+# We create 3 statistics manually which is the minimum needed to
+# create a forecast and a partial statistic on column A so that a
+# merged statistics is also generated.
 exec-sql
 CREATE STATISTICS __auto__ ON a FROM tab;
 CREATE STATISTICS __auto__ ON b FROM tab;
 CREATE STATISTICS __auto__ ON a FROM tab;
 CREATE STATISTICS __auto__ ON b FROM tab;
 CREATE STATISTICS __auto__ ON a FROM tab;
 CREATE STATISTICS __auto__ ON b FROM tab;
+CREATE STATISTICS partial  ON a FROM tab USING EXTREMES;
+----
+
+query-sql
+SELECT count(1) FROM [ SHOW STATISTICS FOR TABLE tab ]
 ----
+7
 
-# The previous bug occurs when there are two or more forecasts since
-# forecasts do not hava a statistics ID.
 query-sql
 SELECT count(1) FROM [ SHOW STATISTICS FOR TABLE tab WITH FORECAST ] WHERE statistics_name = '__forecast__'
 ----
 2
 
+query-sql
+SELECT count(1) FROM [ SHOW STATISTICS FOR TABLE tab WITH MERGE ] WHERE statistics_name = '__merged__'
+----
+1
+
 exec-sql
 BACKUP DATABASE db1 INTO 'nodelocal://0/test/'
 ----
+
+# TODO(ssd): The expectation here is 6 stats rather than 7 because the
+# 'partial' stat is not backed up even though it is persisted. I think
+# we may want a different API for fetching statistics.
+query-sql
+SELECT
+    json_array_length(
+        crdb_internal.pb_to_json(
+            'cockroach.ccl.backupccl.StatsTable',
+            crdb_internal.read_file(
+                concat(
+                    'nodelocal://0/test/',
+                    (SELECT PATH FROM [SHOW BACKUPS IN 'nodelocal://0/test/']),
+                    '/BACKUP-STATISTICS'
+                )
+            )
+        )
+        -> 'statistics'
+    )
+----
+6