Review fix

src/Core/Settings.h

@@ -723,7 +723,7 @@ class IColumn;
     M(Bool, skip_download_if_exceeds_query_cache, true, "Skip download from remote filesystem if exceeds query cache size", 0) \
     M(UInt64, filesystem_cache_max_download_size, (128UL * 1024 * 1024 * 1024), "Max remote filesystem cache size that can be downloaded by a single query", 0) \
     M(Bool, throw_on_error_from_cache_on_write_operations, false, "Ignore error from cache when caching on write operations (INSERT, merges)", 0) \
-    M(UInt64, filesystem_cache_getorset_batch_size, 20, "A batch size for holding file segments for a single read range", 0) \
+    M(UInt64, filesystem_cache_segments_batch_size, 20, "Limit on size of a single batch of file segments that a read buffer can request from cache. Too low value will lead to excessive requests to cache, too large may slow down eviction from cache", 0) \
     \
     M(Bool, load_marks_asynchronously, false, "Load MergeTree marks asynchronously", 0) \
     M(Bool, enable_filesystem_read_prefetches_log, false, "Log to system.filesystem prefetch_log during query. Should be used only for testing or debugging, not recommended to be turned on by default", 0) \

src/Disks/IO/CachedOnDiskReadBufferFromFile.cpp

@@ -116,18 +116,19 @@ void CachedOnDiskReadBufferFromFile::appendFilesystemCacheLog(
 
 bool CachedOnDiskReadBufferFromFile::nextFileSegmentsBatch()
 {
+    chassert(!file_segments || file_segments->empty());
     size_t size = getRemainingSizeToRead();
     if (!size)
         return false;
 
     if (settings.read_from_filesystem_cache_if_exists_otherwise_bypass_cache)
     {
-        file_segments = cache->get(cache_key, file_offset_of_buffer_end, size, settings.filesystem_cache_getorset_batch_size);
+        file_segments = cache->get(cache_key, file_offset_of_buffer_end, size, settings.filesystem_cache_segments_batch_size);
     }
     else
     {
         CreateFileSegmentSettings create_settings(FileSegmentKind::Regular);
-        file_segments = cache->getOrSet(cache_key, file_offset_of_buffer_end, size, file_size.value(), create_settings, settings.filesystem_cache_getorset_batch_size);
+        file_segments = cache->getOrSet(cache_key, file_offset_of_buffer_end, size, file_size.value(), create_settings, settings.filesystem_cache_segments_batch_size);
     }
     return !file_segments->empty();
 }

src/IO/ReadSettings.h

@@ -100,7 +100,7 @@ struct ReadSettings
     bool enable_filesystem_cache_log = false;
     /// Don't populate cache when the read is not part of query execution (e.g. background thread).
     bool avoid_readthrough_cache_outside_query_context = true;
-    size_t filesystem_cache_getorset_batch_size = 100;
+    size_t filesystem_cache_segments_batch_size = 20;
 
     size_t filesystem_cache_max_download_size = (128UL * 1024 * 1024 * 1024);
     bool skip_download_if_exceeds_query_cache = true;

src/Interpreters/Context.cpp

@@ -4761,7 +4761,7 @@ ReadSettings Context::getReadSettings() const
     res.enable_filesystem_cache = settings.enable_filesystem_cache;
     res.read_from_filesystem_cache_if_exists_otherwise_bypass_cache = settings.read_from_filesystem_cache_if_exists_otherwise_bypass_cache;
     res.enable_filesystem_cache_log = settings.enable_filesystem_cache_log;
-    res.filesystem_cache_getorset_batch_size = settings.filesystem_cache_getorset_batch_size;
+    res.filesystem_cache_segments_batch_size = settings.filesystem_cache_segments_batch_size;
 
     res.filesystem_cache_max_download_size = settings.filesystem_cache_max_download_size;
     res.skip_download_if_exceeds_query_cache = settings.skip_download_if_exceeds_query_cache;