Merge pull request #26120 from lthaooo/settings-merge_selecting_sleep_ms

add merge_selecting_sleep_ms setting

docs/en/operations/settings/settings.md

@@ -1998,6 +1998,16 @@ Possible values:
 
 Default value: 16.
 
+## merge_selecting_sleep_ms {#merge_selecting_sleep_ms}
+
+Sleep time for merge selecting when no part selected, a lower setting will trigger selecting tasks in background_schedule_pool frequently which result in large amount of requests to zookeeper in large-scale clusters
+
+Possible values:
+
+-   Any positive integer.
+
+Default value: 5000 
+
 ## parallel_distributed_insert_select {#parallel_distributed_insert_select}
 
 Enables parallel distributed `INSERT ... SELECT` query.

src/Storages/MergeTree/MergeTreeSettings.h

@@ -57,6 +57,7 @@ struct Settings;
     M(Bool, in_memory_parts_insert_sync, false, "If true insert of part with in-memory format will wait for fsync of WAL", 0) \
     M(UInt64, non_replicated_deduplication_window, 0, "How many last blocks of hashes should be kept on disk (0 - disabled).", 0) \
     M(UInt64, max_parts_to_merge_at_once, 100, "Max amount of parts which can be merged at once (0 - disabled). Doesn't affect OPTIMIZE FINAL query.", 0) \
+    M(UInt64, merge_selecting_sleep_ms, 5000, "Sleep time for merge selecting when no part selected, a lower setting will trigger selecting tasks in background_schedule_pool frequently which result in large amount of requests to zookeeper in large-scale clusters", 0) \
     \
     /** Inserts settings. */ \
     M(UInt64, parts_to_delay_insert, 150, "If table contains at least that many active parts in single partition, artificially slow down insert into table.", 0) \

src/Storages/StorageReplicatedMergeTree.cpp

@@ -155,7 +155,6 @@ namespace ActionLocks
 
 
 static const auto QUEUE_UPDATE_ERROR_SLEEP_MS        = 1 * 1000;
-static const auto MERGE_SELECTING_SLEEP_MS           = 5 * 1000;
 static const auto MUTATIONS_FINALIZING_SLEEP_MS      = 1 * 1000;
 static const auto MUTATIONS_FINALIZING_IDLE_SLEEP_MS = 5 * 1000;
 
@@ -3346,7 +3345,7 @@ void StorageReplicatedMergeTree::mergeSelectingTask()
     if (create_result != CreateMergeEntryResult::Ok
         && create_result != CreateMergeEntryResult::LogUpdated)
     {
-        merge_selecting_task->scheduleAfter(MERGE_SELECTING_SLEEP_MS);
+        merge_selecting_task->scheduleAfter(storage_settings_ptr->merge_selecting_sleep_ms);
     }
     else
     {