[fix](scanner) Fix incorrect _max_thread_num in scanner context when many queries are running.

be/src/pipeline/exec/scan_operator.cpp

@@ -997,16 +997,7 @@ Status ScanLocalState<Derived>::_start_scanners(
  auto& p = _parent->cast<typename Derived::Parent>();
  _scanner_ctx = vectorized::ScannerContext::create_shared(
  state(), this, p._output_tuple_desc, p.output_row_descriptor(), scanners, p.limit(),
- state()->scan_queue_mem_limit(), _scan_dependency,
- // NOTE: This will logic makes _max_thread_num of ScannerContext to be C(num of cores) * 2
- // For a query with C/2 instance and M scan node, scan task of this query will be C/2 * M * C*2
- // and will be C*C*N at most.
- // 1. If data distribution is ignored , we use 1 instance to scan.
- // 2. Else if this operator is not file scan operator, we use config::doris_scanner_thread_pool_thread_num scanners to scan.
- // 3. Else, file scanner will consume much memory so we use config::doris_scanner_thread_pool_thread_num / query_parallel_instance_num scanners to scan.
- p.ignore_data_distribution() || !p.is_file_scan_operator()
- ? 1
- : state()->query_parallel_instance_num());
+ _scan_dependency, p.ignore_data_distribution());
  return Status::OK();
 }
 

be/src/vec/exec/scan/scanner_context.cpp

@@ -23,16 +23,19 @@
 
 #include <mutex>
 #include <ostream>
+#include <tuple>
 #include <utility>
 
 #include "common/config.h"
 #include "common/status.h"
+#include "olap/tablet.h"
 #include "pipeline/exec/scan_operator.h"
 #include "runtime/descriptors.h"
 #include "runtime/exec_env.h"
 #include "runtime/runtime_state.h"
 #include "util/uid_util.h"
 #include "vec/core/block.h"
+#include "vec/exec/scan/scanner_scheduler.h"
 #include "vec/exec/scan/vscan_node.h"
 
 namespace doris::vectorized {
@@ -43,8 +46,7 @@ ScannerContext::ScannerContext(
  RuntimeState* state, pipeline::ScanLocalStateBase* local_state,
  const TupleDescriptor* output_tuple_desc, const RowDescriptor* output_row_descriptor,
  const std::list<std::shared_ptr<vectorized::ScannerDelegate>>& scanners, int64_t limit_,
- int64_t max_bytes_in_blocks_queue, std::shared_ptr<pipeline::Dependency> dependency,
- const int num_parallel_instances)
+ std::shared_ptr<pipeline::Dependency> dependency, bool ignore_data_distribution)
  : HasTaskExecutionCtx(state),
  _state(state),
  _local_state(local_state),
@@ -54,53 +56,142 @@ ScannerContext::ScannerContext(
  _output_row_descriptor(output_row_descriptor),
  _batch_size(state->batch_size()),
  limit(limit_),
- _max_bytes_in_queue(std::max(max_bytes_in_blocks_queue, (int64_t)1024) *
- num_parallel_instances),
- _scanner_scheduler(state->exec_env()->scanner_scheduler()),
+ _scanner_scheduler_global(state->exec_env()->scanner_scheduler()),
  _all_scanners(scanners.begin(), scanners.end()),
-_num_parallel_instances(num_parallel_instances) {
+_ignore_data_distribution(ignore_data_distribution) {
  DCHECK(_output_row_descriptor == nullptr ||
  _output_row_descriptor->tuple_descriptors().size() == 1);
  _query_id = _state->get_query_ctx()->query_id();
  ctx_id = UniqueId::gen_uid().to_string();
+ _scanners.enqueue_bulk(scanners.begin(), scanners.size());
+ if (limit < 0) {
+ limit = -1;
+ }
+ MAX_SCALE_UP_RATIO = _state->scanner_scale_up_ratio();
+ _query_thread_context = {_query_id, _state->query_mem_tracker(),
+ _state->get_query_ctx()->workload_group()};
+ _dependency = dependency;
+
+ DorisMetrics::instance()->scanner_ctx_cnt->increment(1);
+}
+
+// After init function call, should not access _parent
+Status ScannerContext::init() {
+ _scanner_profile = _local_state->_scanner_profile;
+ _scanner_sched_counter = _local_state->_scanner_sched_counter;
+ _newly_create_free_blocks_num = _local_state->_newly_create_free_blocks_num;
+ _scanner_wait_batch_timer = _local_state->_scanner_wait_batch_timer;
+ _scanner_ctx_sched_time = _local_state->_scanner_ctx_sched_time;
+ _scale_up_scanners_counter = _local_state->_scale_up_scanners_counter;
+ _scanner_memory_used_counter = _local_state->_memory_used_counter;
+
+#ifndef BE_TEST
+ // 3. get thread token
+ if (!_state->get_query_ctx()) {
+ return Status::InternalError("Query context of {} is not set",
+ print_id(_state->query_id()));
+ }
+
+ thread_token = _state->get_query_ctx()->get_token();
+
+ if (_state->get_query_ctx()->get_scan_scheduler()) {
+ _should_reset_thread_name = false;
+ }
+
+#endif
+ _local_state->_runtime_profile->add_info_string("UseSpecificThreadToken",
+ thread_token == nullptr ? "False" : "True");
+
+ const int num_parallel_instances = _state->query_parallel_instance_num();
+
+ // _max_bytes_in_queue controls the maximum memory that can be used by a single scan instance.
+ // scan_queue_mem_limit on FE is 100MB by default, on backend we will make sure its actual value
+ // is larger than 10MB.
+ _max_bytes_in_queue = std::max(_state->scan_queue_mem_limit(), (int64_t)1024 * 1024 * 10);
+
  // Provide more memory for wide tables, increase proportionally by multiples of 300
  _max_bytes_in_queue *= _output_tuple_desc->slots().size() / 300 + 1;
- if (scanners.empty()) {
+
+ // TODO: Where is the proper position to place this code?
+ if (_all_scanners.empty()) {
  _is_finished = true;
  _set_scanner_done();
  }
- _scanners.enqueue_bulk(scanners.begin(), scanners.size());
- if (limit < 0) {
- limit = -1;
+
+ // This is a track implementation.
+ // The logic is kept only for the purpose of the potential performance issue.
+ bool submit_many_scan_tasks_for_potential_performance_issue = true;
+ auto scanner = _all_scanners.front().lock();
+ DCHECK(scanner != nullptr);
+ // A query could have remote scan task and local scan task at the same time.
+ // So we need to compute the _scanner_scheduler in each scan operator instead of query context.
+ SimplifiedScanScheduler* simple_scan_scheduler = _state->get_query_ctx()->get_scan_scheduler();
+ SimplifiedScanScheduler* remote_scan_task_scheduler =
+ _state->get_query_ctx()->get_remote_scan_scheduler();
+ if (scanner->_scanner->get_storage_type() == TabletStorageType::STORAGE_TYPE_LOCAL) {
+ // scan_scheduler could be empty if query does not have a workload group.
+ if (simple_scan_scheduler) {
+ _scanner_scheduler = simple_scan_scheduler;
+ } else {
+ _scanner_scheduler = _scanner_scheduler_global->get_local_scan_thread_pool();
+ }
+ } else {
+ // remote_scan_task_scheduler could be empty if query does not have a workload group.
+ if (remote_scan_task_scheduler) {
+ _scanner_scheduler = remote_scan_task_scheduler;
+ } else {
+ _scanner_scheduler = _scanner_scheduler_global->get_remote_scan_thread_pool();
+ }
  }
- MAX_SCALE_UP_RATIO = _state->scanner_scale_up_ratio();
+
+ // _scannner_scheduler will be used to submit scan task.
+ if (_scanner_scheduler->get_queue_size() * 2 > config::doris_scanner_thread_pool_queue_size) {
+ submit_many_scan_tasks_for_potential_performance_issue = false;
+ }
+
  // _max_thread_num controls how many scanners of this ScanOperator can be submitted to scheduler at a time.
  // The overall target of our system is to make full utilization of the resources.
- // At the same time, we dont want too many tasks are queued by scheduler, that makes the query
- // waiting too long, and existing task can not be scheduled in time.
- // First of all, we try to make sure _max_thread_num of a ScanNode of a query on a single backend is less than
- // config::doris_scanner_thread_pool_thread_num.
+ // At the same time, we dont want too many tasks are queued by scheduler, that is not necessary.
+ // So, first of all, we try to make sure _max_thread_num of a ScanNode of a query on a single backend is less than
+ // 2 * config::doris_scanner_thread_pool_thread_num, so that we can make all io threads busy.
  // For example, on a 64-core machine, the default value of config::doris_scanner_thread_pool_thread_num will be 64*2 =128.
  // and the num_parallel_instances of this scan operator will be 64/2=32.
- // For a query who has two scan nodes, the _max_thread_num of each scan node instance will be 128 / 32 = 4.
- // We have 32 instances of this scan operator, so for the ScanNode, we have 4 * 32 = 128 scanner tasks can be submitted at a time.
- // Remember that we have to ScanNode in this query, so the total number of scanner tasks can be submitted at a time is 128 * 2 = 256.
- _max_thread_num =
- _state->num_scanner_threads() > 0
- ? _state->num_scanner_threads()
- : config::doris_scanner_thread_pool_thread_num / num_parallel_instances;
+ // For a query who has one scan nodes, the _max_thread_num of each scan node instance will be 4 * 128 / 32 = 16.
+ // We have 32 instances of this scan operator, so for the ScanNode, we have 16 * 32 = 8 * 64 = 512 scanner tasks can be submitted at a time.
+ _max_thread_num = _state->num_scanner_threads() > 0 ? _state->num_scanner_threads() : 0;
+
+ if (_max_thread_num == 0) {
+ // NOTE: When ignore_data_distribution is true, the parallelism
+ // of the scan operator is regarded as 1 (actually maybe not).
+ // That will make the number of scan task can be submitted to the scheduler
+ // in a vary large value. This logicl is kept from the older implementation.
+ if (submit_many_scan_tasks_for_potential_performance_issue || _ignore_data_distribution) {
+ _max_thread_num = config::doris_scanner_thread_pool_thread_num / 1;
+ } else {
+ _max_thread_num =
+ 4 * (config::doris_scanner_thread_pool_thread_num / num_parallel_instances);
+ // In some rare cases, user may set num_parallel_instances to 1 handly to make many query could be executed
+ // in parallel. We need to make sure the _max_thread_num is smaller than previous value.
+ _max_thread_num =
+ std::min(_max_thread_num, config::doris_scanner_thread_pool_thread_num);
+ }
+ }
+
  _max_thread_num = _max_thread_num == 0 ? 1 : _max_thread_num;
  // In some situation, there are not too many big tablets involed, so we can reduce the thread number.
- _max_thread_num = std::min(_max_thread_num, (int32_t)scanners.size());
+ // NOTE: when _all_scanners.size is zero, the _max_thread_num will be 0.
+ _max_thread_num = std::min(_max_thread_num, (int32_t)_all_scanners.size());
+
  // 1. Calculate max concurrency
  // For select * from table limit 10; should just use one thread.
  if (_local_state->should_run_serial()) {
  _max_thread_num = 1;
  }
+
  // when user not specify scan_thread_num, so we can try downgrade _max_thread_num.
  // becaue we found in a table with 5k columns, column reader may ocuppy too much memory.
  // you can refer https://github.com/apache/doris/issues/35340 for details.
- int32_t max_column_reader_num = state->query_options().max_column_reader_num;
+ int32_t max_column_reader_num = _state->query_options().max_column_reader_num;
  if (_max_thread_num != 1 && max_column_reader_num > 0) {
  int32_t scan_column_num = _output_tuple_desc->slots().size();
  int32_t current_column_num = scan_column_num * _max_thread_num;
@@ -110,46 +201,15 @@ ScannerContext::ScannerContext(
  if (new_max_thread_num < _max_thread_num) {
  int32_t origin_max_thread_num = _max_thread_num;
  _max_thread_num = new_max_thread_num;
- LOG(INFO) << "downgrade query:" << print_id(state->query_id())
+ LOG(INFO) << "downgrade query:" << print_id(_state->query_id())
  << " scan's max_thread_num from " << origin_max_thread_num << " to "
  << _max_thread_num << ",column num: " << scan_column_num
  << ", max_column_reader_num: " << max_column_reader_num;
  }
  }
  }
 
- _query_thread_context = {_query_id, _state->query_mem_tracker(),
- _state->get_query_ctx()->workload_group()};
- _dependency = dependency;
-
- DorisMetrics::instance()->scanner_ctx_cnt->increment(1);
-}
-
-// After init function call, should not access _parent
-Status ScannerContext::init() {
- _scanner_profile = _local_state->_scanner_profile;
- _scanner_sched_counter = _local_state->_scanner_sched_counter;
- _newly_create_free_blocks_num = _local_state->_newly_create_free_blocks_num;
- _scanner_wait_batch_timer = _local_state->_scanner_wait_batch_timer;
- _scanner_ctx_sched_time = _local_state->_scanner_ctx_sched_time;
- _scale_up_scanners_counter = _local_state->_scale_up_scanners_counter;
- _scanner_memory_used_counter = _local_state->_memory_used_counter;
-
-#ifndef BE_TEST
- // 3. get thread token
- if (_state->get_query_ctx()) {
- thread_token = _state->get_query_ctx()->get_token();
- _simple_scan_scheduler = _state->get_query_ctx()->get_scan_scheduler();
- if (_simple_scan_scheduler) {
- _should_reset_thread_name = false;
- }
- _remote_scan_task_scheduler = _state->get_query_ctx()->get_remote_scan_scheduler();
- }
-#endif
-
  COUNTER_SET(_local_state->_max_scanner_thread_num, (int64_t)_max_thread_num);
- _local_state->_runtime_profile->add_info_string("UseSpecificThreadToken",
- thread_token == nullptr ? "False" : "True");
 
  // submit `_max_thread_num` running scanners to `ScannerScheduler`
  // When a running scanners is finished, it will submit one of the remaining scanners.
@@ -205,7 +265,7 @@ bool ScannerContext::empty_in_queue(int id) {
 Status ScannerContext::submit_scan_task(std::shared_ptr<ScanTask> scan_task) {
  _scanner_sched_counter->update(1);
  _num_scheduled_scanners++;
- return _scanner_scheduler->submit(shared_from_this(), scan_task);
+ return _scanner_scheduler_global->submit(shared_from_this(), scan_task);
 }
 
 void ScannerContext::append_block_to_queue(std::shared_ptr<ScanTask> scan_task) {

be/src/vec/exec/scan/scanner_context.h

@@ -107,9 +107,8 @@ class ScannerContext : public std::enable_shared_from_this<ScannerContext>,
  const TupleDescriptor* output_tuple_desc,
  const RowDescriptor* output_row_descriptor,
  const std::list<std::shared_ptr<vectorized::ScannerDelegate>>& scanners,
- int64_t limit_, int64_t max_bytes_in_blocks_queue,
- std::shared_ptr<pipeline::Dependency> dependency,
- const int num_parallel_instances);
+ int64_t limit_, std::shared_ptr<pipeline::Dependency> dependency,
+ bool ignore_data_distribution);
 
  ~ScannerContext() override {
  SCOPED_SWITCH_THREAD_MEM_TRACKER_LIMITER(_query_thread_context.query_mem_tracker);
@@ -162,9 +161,7 @@ class ScannerContext : public std::enable_shared_from_this<ScannerContext>,
 
  bool empty_in_queue(int id);
 
- SimplifiedScanScheduler* get_simple_scan_scheduler() { return _simple_scan_scheduler; }
-
- SimplifiedScanScheduler* get_remote_scan_scheduler() { return _remote_scan_task_scheduler; }
+ SimplifiedScanScheduler* get_scan_scheduler() { return _scanner_scheduler; }
 
  void stop_scanners(RuntimeState* state);
 
@@ -212,17 +209,15 @@ class ScannerContext : public std::enable_shared_from_this<ScannerContext>,
  int64_t limit;
 
  int32_t _max_thread_num = 0;
- int64_t _max_bytes_in_queue;
- doris::vectorized::ScannerScheduler* _scanner_scheduler;
- SimplifiedScanScheduler* _simple_scan_scheduler = nullptr;
- SimplifiedScanScheduler* _remote_scan_task_scheduler = nullptr;
+ int64_t _max_bytes_in_queue = 0;
+ doris::vectorized::ScannerScheduler* _scanner_scheduler_global = nullptr;
+ SimplifiedScanScheduler* _scanner_scheduler = nullptr;
  moodycamel::ConcurrentQueue<std::weak_ptr<ScannerDelegate>> _scanners;
  int32_t _num_scheduled_scanners = 0;
  int32_t _num_finished_scanners = 0;
  int32_t _num_running_scanners = 0;
  // weak pointer for _scanners, used in stop function
  std::vector<std::weak_ptr<ScannerDelegate>> _all_scanners;
- const int _num_parallel_instances;
  std::shared_ptr<RuntimeProfile> _scanner_profile;
  RuntimeProfile::Counter* _scanner_sched_counter = nullptr;
  // This counter refers to scan operator's local state
@@ -233,6 +228,7 @@ class ScannerContext : public std::enable_shared_from_this<ScannerContext>,
  RuntimeProfile::Counter* _scale_up_scanners_counter = nullptr;
  QueryThreadContext _query_thread_context;
  std::shared_ptr<pipeline::Dependency> _dependency = nullptr;
+ bool _ignore_data_distribution = false;
 
  // for scaling up the running scanners
  size_t _estimated_block_size = 0;

be/src/vec/exec/scan/scanner_scheduler.cpp

@@ -170,13 +170,7 @@ Status ScannerScheduler::submit(std::shared_ptr<ScannerContext> ctx,
  scanner_delegate->_scanner->start_wait_worker_timer();
  TabletStorageType type = scanner_delegate->_scanner->get_storage_type();
  auto sumbit_task = [&]() {
- bool is_local = type == TabletStorageType::STORAGE_TYPE_LOCAL;
- SimplifiedScanScheduler* scan_sched =
- is_local ? ctx->get_simple_scan_scheduler() : ctx->get_remote_scan_scheduler();
- if (!scan_sched) { // query without workload group
- scan_sched =
- is_local ? _local_scan_thread_pool.get() : _remote_scan_thread_pool.get();
- }
+ SimplifiedScanScheduler* scan_sched = ctx->get_scan_scheduler();
  auto work_func = [scanner_ref = scan_task, ctx]() {
  DorisMetrics::instance()->scanner_task_queued->increment(-1);
  DorisMetrics::instance()->scanner_task_running->increment(1);

be/src/vec/exec/scan/scanner_scheduler.h

@@ -72,6 +72,12 @@ class ScannerScheduler {
 
  static int get_remote_scan_thread_queue_size();
 
+ SimplifiedScanScheduler* get_local_scan_thread_pool() { return _local_scan_thread_pool.get(); }
+
+ SimplifiedScanScheduler* get_remote_scan_thread_pool() {
+ return _remote_scan_thread_pool.get();
+ }
+
 private:
  static void _scanner_scan(std::shared_ptr<ScannerContext> ctx,
  std::shared_ptr<ScanTask> scan_task);

fe/fe-core/src/main/java/org/apache/doris/qe/SessionVariable.java

@@ -698,7 +698,10 @@ public class SessionVariable implements Serializable, Writable {
  @VariableMgr.VarAttr(name = EXEC_MEM_LIMIT)
  public long maxExecMemByte = 2147483648L;
 
- @VariableMgr.VarAttr(name = SCAN_QUEUE_MEM_LIMIT)
+ @VariableMgr.VarAttr(name = SCAN_QUEUE_MEM_LIMIT,
+ description = {"每个 Scan Instance 的 block queue 能够保存多少字节的 block",
+ "How many bytes of block can be saved in the block queue of each Scan Instance"})
+ // 100MB
  public long maxScanQueueMemByte = 2147483648L / 20;
 
  @VariableMgr.VarAttr(name = NUM_SCANNER_THREADS, needForward = true, description = {