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MergeTreePrefetchedReadPool disable for LIMIT only queries #58505

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merged 3 commits into from Jan 4, 2024
Merged

MergeTreePrefetchedReadPool disable for LIMIT only queries #58505

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b5997e6
MergeTreePrefetchedReadPool disable for LIMIT only queries
kitaisreal Jan 4, 2024
8573c66
Fixed code review issues
kitaisreal Jan 4, 2024
d9f68f4
Fixed tests
kitaisreal Jan 4, 2024
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7 changes: 6 additions & 1 deletion src/Interpreters/InterpreterSelectQuery.cpp
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Expand Up @@ -2501,7 +2501,12 @@ void InterpreterSelectQuery::executeFetchColumns(QueryProcessingStage::Enum proc
max_block_size = std::max<UInt64>(1, max_block_limited);
max_threads_execute_query = max_streams = 1;
}
if (max_block_limited < local_limits.local_limits.size_limits.max_rows)
if (local_limits.local_limits.size_limits.max_rows != 0)
{
if (max_block_limited < local_limits.local_limits.size_limits.max_rows)
query_info.limit = max_block_limited;
}
else
{
query_info.limit = max_block_limited;
}
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7 changes: 6 additions & 1 deletion src/Planner/PlannerJoinTree.cpp
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Expand Up @@ -645,7 +645,12 @@ JoinTreeQueryPlan buildQueryPlanForTableExpression(QueryTreeNodePtr table_expres
max_threads_execute_query = 1;
}

if (max_block_size_limited < select_query_info.local_storage_limits.local_limits.size_limits.max_rows)
if (select_query_info.local_storage_limits.local_limits.size_limits.max_rows != 0)
{
if (max_block_size_limited < select_query_info.local_storage_limits.local_limits.size_limits.max_rows)
table_expression_query_info.limit = max_block_size_limited;
}
else
{
table_expression_query_info.limit = max_block_size_limited;
}
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8 changes: 7 additions & 1 deletion src/Processors/QueryPlan/ReadFromMergeTree.cpp
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Expand Up @@ -418,7 +418,13 @@ Pipe ReadFromMergeTree::readFromPool(
&& settings.allow_prefetched_read_pool_for_local_filesystem
&& MergeTreePrefetchedReadPool::checkReadMethodAllowed(reader_settings.read_settings.local_fs_method);

if (allow_prefetched_remote || allow_prefetched_local)
/** Do not use prefetched read pool if query is trivial limit query.
* Because time spend during filling per thread tasks can be greater than whole query
* execution for big tables with small limit.
*/
bool use_prefetched_read_pool = query_info.limit != 0 && (allow_prefetched_remote || allow_prefetched_local);

if (use_prefetched_read_pool)
{
pool = std::make_shared<MergeTreePrefetchedReadPool>(
std::move(parts_with_range),
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