Configure memory settings for ClickHouse merges

Added configuration options to reduce memory usage during merges in the system.metric_log table.

Author: lesandie

content/en/altinity-kb-setup-and-maintenance/configure_clickhouse_for_low_mem_envs.md

@@ -44,6 +44,9 @@ TLDR;
     <number_of_free_entries_in_pool_to_lower_max_size_of_merge>2</number_of_free_entries_in_pool_to_lower_max_size_of_merge>
     <number_of_free_entries_in_pool_to_execute_mutation>2</number_of_free_entries_in_pool_to_execute_mutation>
     <number_of_free_entries_in_pool_to_execute_optimize_entire_partition>2</number_of_free_entries_in_pool_to_execute_optimize_entire_partition>
+    <!-- Reduces memory usage during merges in system.metric_log table (enabled by default) by setting min_bytes_for_wide_part and vertical_merge_algorithm_min_bytes_to_activate to 128MB -->
+    <min_bytes_for_wide_part>134217728</min_bytes_for_wide_part>
+    <vertical_merge_algorithm_min_bytes_to_activate>134217728</vertical_merge_algorithm_min_bytes_to_activate>
   </merge_tree>
 
   <!-- shrink all pools to minimum-->