Merge pull request ClickHouse#80572 from rschu1ze/zero-prefetch-setting

Complain earlier about `filesystem_prefetch_max_memory_usage = 0`

Author: rschu1ze

src/Core/Settings.cpp

@@ -5649,7 +5649,7 @@ Prefetch step in bytes. Zero means `auto` - approximately the best prefetch step
     DECLARE(UInt64, filesystem_prefetch_step_marks, 0, R"(
 Prefetch step in marks. Zero means `auto` - approximately the best prefetch step will be auto deduced, but might not be 100% the best. The actual value might be different because of setting filesystem_prefetch_min_bytes_for_single_read_task
 )", 0) \
-    DECLARE(UInt64, filesystem_prefetch_max_memory_usage, "1Gi", R"(
+    DECLARE(NonZeroUInt64, filesystem_prefetch_max_memory_usage, "1Gi", R"(
 Maximum memory usage for prefetches.
 )", 0) \
     DECLARE(UInt64, filesystem_prefetches_limit, 200, R"(

src/Storages/MergeTree/MergeTreePrefetchedReadPool.cpp

@@ -27,11 +27,11 @@ namespace DB
 {
 namespace Setting
 {
-    extern const SettingsUInt64 filesystem_prefetches_limit;
-    extern const SettingsUInt64 filesystem_prefetch_max_memory_usage;
-    extern const SettingsUInt64 filesystem_prefetch_step_marks;
-    extern const SettingsUInt64 filesystem_prefetch_step_bytes;
+    extern const SettingsNonZeroUInt64 filesystem_prefetch_max_memory_usage;
     extern const SettingsBool merge_tree_determine_task_size_by_prewhere_columns;
+    extern const SettingsUInt64 filesystem_prefetch_step_bytes;
+    extern const SettingsUInt64 filesystem_prefetch_step_marks;
+    extern const SettingsUInt64 filesystem_prefetches_limit;
     extern const SettingsUInt64 prefetch_buffer_size;
 }
 
@@ -420,8 +420,6 @@ void MergeTreePrefetchedReadPool::fillPerThreadTasks(size_t threads, size_t sum_
         total_size_approx);
 
     size_t allowed_memory_usage = settings[Setting::filesystem_prefetch_max_memory_usage];
-    if (!allowed_memory_usage)
-        throw Exception(ErrorCodes::BAD_ARGUMENTS, "Setting `filesystem_prefetch_max_memory_usage` must be non-zero");
 
     std::optional<size_t> allowed_prefetches_num
         = settings[Setting::filesystem_prefetches_limit] ? std::optional<size_t>(settings[Setting::filesystem_prefetches_limit]) : std::nullopt;

tests/queries/0_stateless/01293_show_settings.reference

@@ -5,7 +5,7 @@ connect_timeout_with_failover_secure_ms	Milliseconds	3000
 external_storage_connect_timeout_sec	UInt64	10
 parallel_replicas_connect_timeout_ms	Milliseconds	300
 s3_connect_timeout_ms	UInt64	1000
-filesystem_prefetch_max_memory_usage	UInt64	1073741824
+filesystem_prefetch_max_memory_usage	NonZeroUInt64	1073741824
 max_memory_usage	UInt64	5000000000
 max_memory_usage_for_user	UInt64	32000000000
 max_untracked_memory	UInt64	1048576

tests/queries/0_stateless/03519_zero_filesystem_prefetch_max_memory_usage.reference

@@ -0,0 +1,3 @@
+-- Checks that session setting 'filesystem_prefetch_max_memory_usage' must not be 0
+
+SET filesystem_prefetch_max_memory_usage = 0; -- { serverError BAD_ARGUMENTS }