tests: avoid extra remote_data_paths usage in 02286_drop_filesystem_cache (slow)

Now it is 2x faster

Author: azat

tests/queries/0_stateless/02286_drop_filesystem_cache.sh

@@ -39,7 +39,6 @@ for STORAGE_POLICY in 's3_cache' 'local_cache' 'azure_cache'; do
 
     $CLICKHOUSE_CLIENT --query "SELECT * FROM test_02286 FORMAT Null"
     $CLICKHOUSE_CLIENT --query "SELECT count() FROM system.filesystem_cache"
-
     $CLICKHOUSE_CLIENT --query "SELECT count()
                                    FROM (
                                        SELECT
@@ -53,20 +52,26 @@ for STORAGE_POLICY in 's3_cache' 'local_cache' 'azure_cache'; do
                                    ON data_paths.cache_path = caches.cache_path"
 
     $CLICKHOUSE_CLIENT --query "DROP TABLE test_02286 SYNC"
-    $CLICKHOUSE_CLIENT --query "SELECT count() FROM system.filesystem_cache"
 
-    $CLICKHOUSE_CLIENT --query "SELECT cache_path FROM system.filesystem_cache"
-    $CLICKHOUSE_CLIENT --query "SELECT cache_path, local_path
-                                   FROM (
-                                       SELECT
-                                           arrayJoin(cache_paths) AS cache_path,
-                                           local_path,
-                                           remote_path
-                                       FROM
-                                           system.remote_data_paths
-                                       ) AS data_paths
-                                   INNER JOIN system.filesystem_cache AS caches
-                                   ON data_paths.cache_path = caches.cache_path"
+    cache_entries=$($CLICKHOUSE_CLIENT --query "SELECT count() FROM system.filesystem_cache")
+    echo "$cache_entries"
+    # system.remote_data_paths is very slow for web disks, so let's avoid extra
+    # call to it (we need it only for debugging of this tests, and only when we
+    # have cache entries, which tests does not expect)
+    if [ $cache_entries -gt 0 ]; then
+        $CLICKHOUSE_CLIENT --query "SELECT cache_path FROM system.filesystem_cache"
+        $CLICKHOUSE_CLIENT --query "SELECT cache_path, local_path
+                                       FROM (
+                                           SELECT
+                                               arrayJoin(cache_paths) AS cache_path,
+                                               local_path,
+                                               remote_path
+                                           FROM
+                                               system.remote_data_paths
+                                           ) AS data_paths
+                                       INNER JOIN system.filesystem_cache AS caches
+                                       ON data_paths.cache_path = caches.cache_path "
+    fi
 
     $CLICKHOUSE_CLIENT --query "DROP TABLE IF EXISTS test_022862"
 done