Allow certain ALTER TABLE commands for plain_rewritable

Currently all alters are disallowed, this is too restrictive. Allow
altering settings (through {MODIFY|RESET} SETTING) and comments (MODIFY
COMMENT).

src/Storages/MergeTree/MergeTreeData.cpp

@@ -3013,8 +3013,11 @@ void MergeTreeData::checkAlterIsPossible(const AlterCommands & commands, Context
                 "Experimental full-text index feature is not enabled (turn on setting 'allow_experimental_inverted_index')");
 
     for (const auto & disk : getDisks())
-        if (!disk->supportsHardLinks())
+        if (!disk->supportsHardLinks() && !commands.isSettingsAlter() && !commands.isCommentAlter())
-            throw Exception(ErrorCodes::SUPPORT_IS_DISABLED, "ALTER TABLE is not supported for immutable disk '{}'", disk->getName());
+            throw Exception(
+                ErrorCodes::SUPPORT_IS_DISABLED,
+                "ALTER TABLE commands are not supported on immutable disk '{}', except for setting and comment alteration",
+                disk->getName());
 
     /// Set of columns that shouldn't be altered.
     NameSet columns_alter_type_forbidden;

tests/integration/test_s3_plain_rewritable/test.py

@@ -80,6 +80,36 @@ def test_insert():
             == insert_values_arr[i]
         )
 
+    for i in range(NUM_WORKERS):
+        nodes[i].query("ALTER TABLE test MODIFY SETTING old_parts_lifetime = 59")
+        assert (
+            nodes[i]
+            .query(
+                "SELECT engine_full from system.tables WHERE database = currentDatabase() AND name = 'test'"
+            )
+            .find("old_parts_lifetime = 59")
+            != -1
+        )
+
+        nodes[i].query("ALTER TABLE test RESET SETTING old_parts_lifetime")
+        assert (
+            nodes[i]
+            .query(
+                "SELECT engine_full from system.tables WHERE database = currentDatabase() AND name = 'test'"
+            )
+            .find("old_parts_lifetime")
+            == -1
+        )
+        nodes[i].query("ALTER TABLE test MODIFY COMMENT 'new description'")
+        assert (
+            nodes[i]
+            .query(
+                "SELECT comment from system.tables WHERE database = currentDatabase() AND name = 'test'"
+            )
+            .find("new description")
+            != -1
+        )
+
 
 @pytest.mark.order(1)
 def test_restart():

tests/queries/0_stateless/03008_local_plain_rewritable.reference

@@ -9,6 +9,7 @@
 4	4	4
 4	7	7
 5	5	5
+1
 10006
 0	0	0
 1	1	1
@@ -20,3 +21,4 @@
 4	4	4
 4	7	7
 5	5	5
+0

tests/queries/0_stateless/03008_local_plain_rewritable.sh

@@ -9,8 +9,10 @@ CUR_DIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
 ${CLICKHOUSE_CLIENT} --query "drop table if exists test_mt sync"
 
 ${CLICKHOUSE_CLIENT} -nm --query "
-create table test_mt (a Int32, b Int64, c Int64) engine = MergeTree() partition by intDiv(a, 1000) order by tuple(a, b)
+create table test_mt (a Int32, b Int64, c Int64)
+engine = MergeTree() partition by intDiv(a, 1000) order by tuple(a, b)
 settings disk = disk(
+    name = disk_s3_plain,
     type = object_storage,
     object_storage_type = local,
     metadata_type = plain_rewritable,
@@ -29,7 +31,23 @@ select (*) from test_mt order by tuple(a, b) limit 10;
 
 ${CLICKHOUSE_CLIENT} --query "optimize table test_mt final"
 
+${CLICKHOUSE_CLIENT} -nm --query "
+alter table test_mt modify setting disk = 'disk_s3_plain', old_parts_lifetime = 3600;
+select engine_full from system.tables WHERE database = currentDatabase() AND name = 'test_mt';
+" | grep -c "old_parts_lifetime = 3600"
+
 ${CLICKHOUSE_CLIENT} -nm --query "
 select count(*) from test_mt;
 select (*) from test_mt order by tuple(a, b) limit 10;
 "
+
+${CLICKHOUSE_CLIENT} -nm --query "
+alter table test_mt update c = 0 where a % 2 = 1;
+alter table test_mt add column d Int64 after c;
+alter table test_mt drop column c;
+" 2>&1 | grep -Fq "SUPPORT_IS_DISABLED"
+
+${CLICKHOUSE_CLIENT} -nm --query "
+truncate table test_mt;
+select count(*) from test_mt;
+"