独家揭秘丨GreatSQL 没开Binlog时多线程插入数据性能劣化之谜

独家揭秘丨GreatSQL 没开Binlog时多线程插入数据性能劣化之谜

一、问题发现

在一次数据迁移中，用到了INSERT INTO t1 SELECT * FROM t2这样的 SQL 用来搬迁大表，为了提高插入效率关闭了Binlog，考虑用多线程来插入提高速度。表的类型信息和插入效率如下所示。

测试环境：

• Linux node-76-11 4.19.90-17.ky10.aarch64，128核CPU，512G内存。

GreatSQL参数配置如下（为降低 I/O 因素影响，关闭 Binlog）：

#**********************Performance*********************
#******connect
max_connections=10000
max_connect_errors=1000000
open_files_limit=65535
back_log=1500
table_definition_cache=10000
thread_stack=256K
thread_cache_size=3000

#******timeout
lock_wait_timeout=600
connect_timeout=10
interactive_timeout=31536000
wait_timeout=31536000
net_read_timeout=86400
net_write_timeout=86400
net_retry_count=10
#**********************InnoDB**************************
transaction_isolation=READ-COMMITTED
innodb_buffer_pool_size=200G
innodb_buffer_pool_instances=16
innodb_max_dirty_pages_pct=90
innodb_flush_log_at_trx_commit=0
innodb_log_buffer_size=1G
innodb_page_cleaners=8
innodb_buffer_pool_dump_at_shutdown=ON
innodb_buffer_pool_load_at_startup=ON
innodb_buffer_pool_dump_pct=100
innodb_checksum_algorithm=NONE
innodb_log_checksums=NO
innodb_undo_log_truncate=OFF
innodb_change_buffering = none
innodb_spin_wait_delay=6
innodb_spin_wait_pause_multiplier=50
innodb_sync_spin_loops=30
#******feature
innodb_open_files=65535
innodb_flush_method=O_DIRECT
innodb_flush_neighbors=0
innodb_flush_sync=ON
innodb_io_capacity=20000
innodb_io_capacity_max=40000
innodb_lru_scan_depth=9000
innodb_lock_wait_timeout=30
innodb_print_all_deadlocks=ON
innodb_online_alter_log_max_size=4G
innodb_thread_concurrency=0
innodb_read_io_threads=32
innodb_write_io_threads=32
innodb_doublewrite=ON
innodb_doublewrite_pages=64
innodb_adaptive_hash_index=OFF
innodb_status_file=OFF

1、窄表 + 有自增主键

greatsql> CREATE TABLE t1 (
c1 int invisible auto_increment primary key,
c2 int,
str1 int DEFAULT(100) NOT NULL,
str2 int DEFAULT(100) NOT NULL,
str3 int DEFAULT(100) NOT NULL,
str4 int DEFAULT(100) NOT NULL
) engine=InnoDB;

greatsql> CREATE TABLE t2 LIKE t1;

行平均长度约 30 字节

2、中等宽度表 + 有自增主键

greatsql> CREATE TABLE t1 (
c1 int invisible auto_increment primary key,
c2 int,
str1 varchar(512) CHARACTER SET latin1 DEFAULT(repeat('a',512)) NOT NULL
) engine=InnoDB;

greatsql> CREATE TABLE t2 LIKE t1;

行平均长度约 500多字节

3、宽表 + 有自增主键

greatsql> CREATE TABLE t1 (
c1 int invisible auto_increment primary key,
c2 int,
str1 varchar(1024) CHARACTER SET latin1 DEFAULT(repeat('a1',512)) NOT NULL,
str2 varchar(1024) CHARACTER SET latin1 DEFAULT(repeat('b2',512)) NOT NULL,
str3 varchar(1024) CHARACTER SET latin1 DEFAULT(repeat('c3',512)) NOT NULL,
str4 varchar(1024) CHARACTER SET latin1 DEFAULT(repeat('c3',512)) NOT NULL
) engine=InnoDB;

greatsql> CREATE TABLE t2 LIKE t1;

行平均长度约 5000多字节

4、窄表 + 无主键（GIPK关）

greatsql> CREATE TABLE t1 (
c1 int invisible auto_increment primary key,
c2 int,
str1 int DEFAULT(100) NOT NULL,
str2 int DEFAULT(100) NOT NULL,
str3 int DEFAULT(100) NOT NULL,
str4 int DEFAULT(100) NOT NULL
) engine=InnoDB;

greatsql> CREATE TABLE t2 (
c2 int,
str1 int DEFAULT(100) NOT NULL,
str2 int DEFAULT(100) NOT NULL,
str3 int DEFAULT(100) NOT NULL,
str4 int DEFAULT(100) NOT NULL
) engine=InnoDB;

行平均宽度约 30 字节，没用 GIPKs 特性

5、结论

从上面的测试结果可以看出，无主键表并发插入劣化严重，有主键的情况下，窄表的并发性能提升效果好，但是对于宽表反而会造成劣化。

二、问题调查过程

1、首先调查无主键的情况下长数据造成性能劣化的情况。用perf查看造成性能劣化的瓶颈在哪里。

+ 12.55% 0.01% mysqld mysqld [.] lock_clust_rec_read_check_and_lock
+ 12.34% 0.13% mysqld [kernel.kallsyms] [k] x64_sys_call
+ 12.03% 0.01% mysqld mysqld [.] Buf_fetch::mtr_add_page
+ 11.92% 0.01% mysqld mysqld [.] btr_cur_ins_lock_and_undo
+ 11.27% 0.19% mysqld [kernel.kallsyms] [k] __x64_sys_futex
- 11.18% 11.11% mysqld mysqld [.] ut_delay
10.89% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 10.75% Query_result_insert::send_data
write_record
handler::ha_write_row
ha_innobase::write_row
row_insert_for_mysql
row_insert_for_mysql_using_ins_graph
row_ins_step
row_ins
row_ins_index_entry_step
row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 10.16% btr_pcur_t::open
- btr_cur_search_to_nth_level
- 10.10% buf_page_get_gen
- 10.08% Buf_fetch::single_page
- 10.07% Buf_fetch::mtr_add_page
rw_lock_x_lock_gen
- pfs_rw_lock_x_lock_func
- 10.07% rw_lock_x_lock_func
ut_delay
+ 11.08% 0.21% mysqld [kernel.kallsyms] [k] do_futex
+ 10.90% 0.02% mysqld mysqld [.] rw_lock_x_lock_func
+ 10.90% 0.00% mysqld mysqld [.] pfs_rw_lock_x_lock_func
+ 10.90% 0.01% mysqld mysqld [.] rw_lock_x_lock_gen
+ 9.44% 0.01% mysqld mysqld [.] locksys::owns_page_shard
+ 9.39% 0.05% mysqld mysqld [.] locksys::Latches::owns_page_shard
+ 9.29% 0.64% mysqld mysqld [.] PolicyMutex >::trylock
+ 7.66% 0.02% mysqld mysqld [.] locksys::rec_queue_latch_and_validate
+ 7.65% 0.17% mysqld mysqld [.] rw_lock_debug_mutex_exit
+ 7.39% 0.07% mysqld mysqld [.] trx_undo_report_row_operation
+ 7.17% 0.01% mysqld mysqld [.] buf_pool_validate_instance
+ 7.17% 0.00% mysqld mysqld [.] buf_validate
- 6.63% 5.87% mysqld mysqld [.] unlikely
- 5.84% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 4.44% Query_result_insert::send_data
write_record
handler::ha_write_row
ha_innobase::write_row
- row_insert_for_mysql
- 4.43% row_insert_for_mysql_using_ins_graph
- 4.42% row_ins_step
- 4.41% row_ins
- 4.41% row_ins_index_entry_step
- 4.35% row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 1.89% btr_pcur_t::open
- btr_cur_search_to_nth_level
- 1.08% page_cur_search_with_match
0.52% dtuple_t::compare
- 1.87% btr_cur_optimistic_insert
1.13% page_cur_tuple_insert
0.56% btr_cur_ins_lock_and_undo
+ 1.40% TableScanIterator::Read
0.76% unlikely
+ 6.38% 0.45% mysqld [kernel.kallsyms] [k] futex_wait
+ 5.88% 0.02% mysqld mysqld [.] Buf_fetch_normal::get
+ 5.76% 0.01% mysqld mysqld [.] lock_rec_lock

可以看到多线程数据插入时候，在无主键的情况下频繁的索引分裂影响性能，所以导致性能劣化严重。

那么有自增主键的情况下性能是什么情况呢？

看一下有自增主键的情况下性能情况，在有自增主键的时候与上面无主键的性能瓶颈处差不多，但是没有那么严重的频繁的索引分裂的性能问题。

+ 10.16% 0.67% mysqld mysqld [.] PolicyMutex<TTASEventMutex<GenericPolicy> >::trylock
+ 9.25% 0.03% mysqld mysqld [.] trx_undo_report_row_operation
+ 8.49% 0.31% mysqld [kernel.kallsyms] [k] futex_wait
+ 7.77% 0.00% mysqld libstdc++.so.6.0.32 [.] 0x00007ffff7958793
+ 7.59% 0.17% mysqld mysqld [.] rw_lock_debug_mutex_exit
- 7.30% 6.87% mysqld mysqld [.] unlikely
6.58% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 5.01% Query_result_insert::send_data
- 5.00% write_record
handler::ha_write_row
- ha_innobase::write_row
- 4.99% row_insert_for_mysql
- row_insert_for_mysql_using_ins_graph
- 4.96% row_ins_step
- row_ins
- 4.95% row_ins_index_entry_step
- 4.91% row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 2.63% btr_cur_optimistic_insert
- 1.35% page_cur_tuple_insert
0.67% page_cur_insert_rec_low
- 0.87% btr_cur_ins_lock_and_undo
0.59% trx_undo_report_row_operation
- 1.22% btr_pcur_t::open
1.20% btr_cur_search_to_nth_level
- 0.55% btr_cur_pessimistic_insert
- 0.55% btr_page_split_and_insert
0.51% page_validate
+ 1.57% TableScanIterator::Read
+ 7.06% 0.03% mysqld mysqld [.] mtr_t::commit
+ 7.02% 0.00% mysqld mysqld [.] buf_validate
+ 7.01% 0.02% mysqld mysqld [.] buf_pool_validate_instance

我们知道对自增主键插入新数据时，是先获取一个区段锁，这样可以避免频繁持锁造成的性能劣化。而无显式定义主键表（其他可用于聚集索引的非空唯一索引也没有）时，会采用实例级的 DB_ROW_ID 作为该表的聚集索引，这个 DB_ROW_ID 每插入一行都需要请求加锁，因此会比自增主键表更加耗时。所以上面可以看到无主键表的多线程插入性能反而比单线程劣化。

2、接着调查有主键的情况下宽表造成性能劣化的情况。用perf查看造成性能劣化的瓶颈在哪里。

+ 12.66% 0.05% mysqld [kernel.kallsyms] [k] do_syscall_64
- 12.65% 12.30% mysqld mysqld [.] ut_delay
- 7.46% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 7.27% Query_result_insert::send_data
write_record
handler::ha_write_row
ha_innobase::write_row
row_insert_for_mysql
row_insert_for_mysql_using_ins_graph
row_ins_step
row_ins
row_ins_index_entry_step
row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 4.53% btr_pcur_t::open
- btr_cur_search_to_nth_level
- 2.52% mtr_t::sx_lock
rw_lock_sx_lock_gen
- pfs_rw_lock_sx_lock_func
+ 2.52% rw_lock_sx_lock_func
- 1.85% buf_page_get_gen
- 1.84% Buf_fetch<Buf_fetch_normal>::single_page
- 1.81% Buf_fetch<Buf_fetch_normal>::mtr_add_page
rw_lock_s_lock_gen
rw_lock_s_lock_func
rw_lock_s_lock_spin
ut_delay
- 2.07% btr_height_get
btr_root_block_get
btr_block_get
btr_block_get_func
- buf_page_get_gen
- 2.06% Buf_fetch<Buf_fetch_normal>::single_page
- 2.05% Buf_fetch<Buf_fetch_normal>::mtr_add_page
rw_lock_s_lock_gen
rw_lock_s_lock_func
rw_lock_s_lock_spin
ut_delay
0.50% btr_cur_optimistic_insert
- 4.85% 0x7ffff7958793
- 4.70% std::thread::_State_impl<std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> > >::_M_run
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::operator()
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::_M_invoke<0ul, 1ul, 2ul>
std::__invoke<Detached_thread, void (*)(unsigned long), unsigned long>
std::__invoke_impl<void, Detached_thread, void (*)(unsigned long), unsigned long>
Detached_thread::operator()<void (*)(unsigned long), unsigned long>
std::_Bind<void (*(unsigned long))(unsigned long)>::operator()<, void>
std::_Bind<void (*(unsigned long))(unsigned long)>::__call<void, , 0ul>
std::__invoke<void (*&)(unsigned long), unsigned long&>
- std::__invoke_impl<void, void (*&)(unsigned long), unsigned long&>
- 4.53% io_handler_thread
- fil_aio_wait
- 4.14% buf_page_io_complete
- 1.48% buf_flush_write_complete
- 1.48% mutex_enter_inline<PolicyMutex<TTASEventMutex<GenericPolicy> > >
PolicyMutex<TTASEventMutex<GenericPolicy> >::enter
TTASEventMutex<GenericPolicy>::enter
TTASEventMutex<GenericPolicy>::spin_and_try_lock
TTASEventMutex<GenericPolicy>::is_free
ut_delay
- 1.38% ibuf_merge_or_delete_for_page
- 1.19% ibuf_bitmap_get_map_page
buf_page_get_gen
Buf_fetch<Buf_fetch_normal>::single_page
Buf_fetch<Buf_fetch_normal>::mtr_add_page
rw_lock_x_lock_gen
pfs_rw_lock_x_lock_func
rw_lock_x_lock_func
ut_delay
- 1.04% mutex_enter_inline<PolicyMutex<TTASEventMutex<GenericPolicy> > >
PolicyMutex<TTASEventMutex<GenericPolicy> >::enter
TTASEventMutex<GenericPolicy>::enter
TTASEventMutex<GenericPolicy>::spin_and_try_lock
TTASEventMutex<GenericPolicy>::is_free
ut_delay
+ 12.57% 0.41% mysqld [kernel.kallsyms] [k] x64_sys_call
+ 9.93% 0.00% mysqld mysqld [.] buf_validate
+ 9.91% 0.06% mysqld mysqld [.] buf_pool_validate_instance
+ 9.73% 0.11% mysqld [kernel.kallsyms] [k] __x64_sys_futex
+ 9.72% 0.30% mysqld mysqld [.] rw_lock_debug_mutex_enter
+ 9.61% 0.13% mysqld [kernel.kallsyms] [k] do_futex
+ 8.23% 0.03% mysqld mysqld [.] TableScanIterator::Read
+ 8.20% 0.02% mysqld mysqld [.] handler::ha_rnd_next
+ 8.17% 0.00% mysqld mysqld [.] ha_innobase::rnd_next
+ 8.17% 0.00% mysqld mysqld [.] ha_innobase::general_fetch
+ 8.08% 0.05% mysqld mysqld [.] row_search_mvcc
+ 7.75% 0.02% mysqld mysqld [.] buf_page_t::Latching_rules_helpers::assert_latches_let_distinguish
+ 7.71% 0.03% mysqld mysqld [.] buf_page_t::is_io_fix_write
+ 7.41% 0.04% mysqld mysqld [.] ut::Stateful_latching_rules<buf_io_fix, 3ul>::assert_latches_let_distinguish
+ 7.10% 0.01% mysqld mysqld [.] btr_cur_optimistic_insert
+ 6.98% 0.02% mysqld mysqld [.] Buf_fetch_normal::get
+ 6.76% 0.29% mysqld mysqld [.] PolicyMutex<TTASEventMutex<GenericPolicy> >::trylock
+ 6.50% 0.02% mysqld mysqld [.] Buf_fetch<Buf_fetch_normal>::mtr_add_page
+ 6.15% 0.04% mysqld mysqld [.] ut::Stateful_latching_rules<buf_io_fix, 3ul>::assert_latches_let_distinguish
+ 6.11% 0.02% mysqld mysqld [.] ut::Stateful_latching_rules<buf_io_fix, 3ul>::can_leave
+ 5.92% 0.27% mysqld [kernel.kallsyms] [k] futex_wait
+ 5.89% 0.11% mysqld mysqld [.] rw_lock_debug_mutex_exit
+ 5.89% 0.01% mysqld mysqld [.] btr_block_get
+ 5.88% 0.00% mysqld mysqld [.] btr_block_get_func
+ 5.74% 0.02% mysqld mysqld [.] rw_lock_s_lock_func
+ 5.50% 0.01% mysqld mysqld [.] PolicyMutex<TTASEventMutex<GenericPolicy> >::enter
- 5.49% 4.80% mysqld mysqld [.] unlikely
- 3.89% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 3.37% Query_result_insert::send_data
write_record
handler::ha_write_row
ha_innobase::write_row
row_insert_for_mysql
row_insert_for_mysql_using_ins_graph
row_ins_step
row_ins
- row_ins_index_entry_step
- 3.33% row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 1.34% btr_pcur_t::open
- 1.34% btr_cur_search_to_nth_level
0.87% page_cur_search_with_match
- 1.26% btr_cur_pessimistic_insert
1.19% btr_page_split_and_insert
+ 0.52% TableScanIterator::Read
0.90% 0x7ffff7958793
0.69% unlikely

可以看到除了上面第一点提到的索引分裂的影响外，还增加了页分裂以及页读写相关的 I/O 操作影响性能，宽表情况下对于读写性能比短数据更加依赖机器的性能和配置，并且会随着写入数据的增加降低写入效率。

同样的，看看单线程情况下宽表的 perf 情况。

+ 8.05% 0.02% mysqld mysqld [.] ut::Stateful_latching_rules<buf_io_fix, 3ul>::can_leave
+ 7.95% 0.00% mysqld mysqld [.] mutex_enter_inline<PolicyMutex<TTASEventMutex<GenericPolicy> > >
+ 7.81% 0.03% mysqld [kernel.kallsyms] [k] x64_sys_call
- 7.50% 7.50% mysqld mysqld [.] ut_delay
- 7.41% 0x7ffff7958793
- 7.36% std::thread::_State_impl<std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> > >::_M_run
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::operator()
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::_M_invoke<0ul, 1ul, 2ul>
std::__invoke<Detached_thread, void (*)(unsigned long), unsigned long>
std::__invoke_impl<void, Detached_thread, void (*)(unsigned long), unsigned long>
Detached_thread::operator()<void (*)(unsigned long), unsigned long>
std::_Bind<void (*(unsigned long))(unsigned long)>::operator()<, void>
std::_Bind<void (*(unsigned long))(unsigned long)>::__call<void, , 0ul>
std::__invoke<void (*&)(unsigned long), unsigned long&>
- std::__invoke_impl<void, void (*&)(unsigned long), unsigned long&>
- 7.34% io_handler_thread
fil_aio_wait
- buf_page_io_complete
- 5.01% buf_flush_write_complete
mutex_enter_inline<PolicyMutex<TTASEventMutex<GenericPolicy> > >
PolicyMutex<TTASEventMutex<GenericPolicy> >::enter
TTASEventMutex<GenericPolicy>::enter
TTASEventMutex<GenericPolicy>::spin_and_try_lock
TTASEventMutex<GenericPolicy>::is_free
ut_delay
- 1.25% ibuf_merge_or_delete_for_page
ibuf_bitmap_get_map_page
buf_page_get_gen
Buf_fetch<Buf_fetch_normal>::single_page
Buf_fetch<Buf_fetch_normal>::mtr_add_page
rw_lock_x_lock_gen
pfs_rw_lock_x_lock_func
rw_lock_x_lock_func
ut_delay
- 1.08% mutex_enter_inline<PolicyMutex<TTASEventMutex<GenericPolicy> > >
PolicyMutex<TTASEventMutex<GenericPolicy> >::enter
TTASEventMutex<GenericPolicy>::enter
TTASEventMutex<GenericPolicy>::spin_and_try_lock
TTASEventMutex<GenericPolicy>::is_free
ut_delay
+ 7.30% 0.04% mysqld mysqld [.] buf_page_t::Latching_rules_helpers::assert_latches_let_distinguish
+ 4.37% 0.00% mysqld mysqld [.] Fil_system::flush_file_spaces
- 4.14% 3.88% mysqld mysqld [.] unlikely
- 2.75% start_thread
pfs_spawn_thread
handle_connection
do_command
dispatch_command
dispatch_sql_command
mysql_execute_command
Sql_cmd_dml::execute
Sql_cmd_dml::execute_inner
Query_expression::execute
- Query_expression::ExecuteIteratorQuery
- 2.46% Query_result_insert::send_data
write_record
handler::ha_write_row
ha_innobase::write_row
row_insert_for_mysql
row_insert_for_mysql_using_ins_graph
row_ins_step
- row_ins
- 2.44% row_ins_index_entry_step
- 2.41% row_ins_index_entry
row_ins_clust_index_entry
- row_ins_clust_index_entry_low
- 0.97% btr_pcur_t::open
- btr_cur_search_to_nth_level
0.55% page_cur_search_with_match
- 0.80% btr_cur_pessimistic_insert
0.70% btr_page_split_and_insert
- 1.13% 0x7ffff7958793
- 1.02% std::thread::_State_impl<std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> > >::_M_run
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::operator()
std::thread::_Invoker<std::tuple<Detached_thread, void (*)(unsigned long), unsigned long> >::_M_invoke<0ul, 1ul, 2ul>
std::__invoke<Detached_thread, void (*)(unsigned long), unsigned long>
std::__invoke_impl<void, Detached_thread, void (*)(unsigned long), unsigned long>
Detached_thread::operator()<void (*)(unsigned long), unsigned long>
std::_Bind<void (*(unsigned long))(unsigned long)>::operator()<, void>
std::_Bind<void (*(unsigned long))(unsigned long)>::__call<void, , 0ul>
std::__invoke<void (*&)(unsigned long), unsigned long&>
- std::__invoke_impl<void, void (*&)(unsigned long), unsigned long&>
- 0.70% io_handler_thread
- fil_aio_wait
- 0.65% buf_page_io_complete
buf_flush_write_complete
dblwr::write_complete
Double_write::write_complete
fil_flush_file_spaces
Fil_system::flush_file_spaces
- Fil_shard::flush_file_spaces
+ 0.65% Fil_shard::acquire
+ 3.97% 0.58% mysqld mysqld [.] Fil_shard::flush_file_spaces

对比多线程和单线程的堆栈信息，可以看到多线程下抢 I/O 资源情况变严重，同时索引分裂和页分裂更严重，要花更多时间进行页位置比较、计算数据占用的空间和插入，另外由于抢锁导致多线程性能劣化更严重。

三、问题解决方案

通过上面分析发现，要想保证多线程插入速度比单线程快需要满足一定的条件：

1. 目标表有主键，当主键列没有设置自增属性的情况下，每个线程间的主键值需要是离散且单个线程内主键值需要连续，这是为了保证索引插入的性能最高。比如线程1主键值为[1-1000]，线程2主键值为[10000-11000]，线程3主键值为[30000-31000]这样排列效率会比[1-3000]分三个线程高很多。
2. 如果目标表主键是自增主键的话，因为无法定义自增主键的值，只能按照插入时候确定键值，因此自增主键会比非自增主键多线程离散值性能慢，但是因为自增主键持有的是区段锁，因此不会频繁持锁方面性能又会比非自增主键好。实际使用的时候还是要看源表的数据分布情况以及目标表结构来决定要怎么分配多线程的插入主键值。
3. 目标表是宽表时，从上面的测试数据来看单行数据超过 520Bytes 多线程就开始劣化了，因此多线程插入只针对窄表有效。

四、问题总结

一般我们都认为多线程插入数据肯定比单线程插入快，但是通过本次的测试和分析可以看到实际情况需要结合数据库参数配置、索引、存储页以及磁盘的 I/O 性能等一起看，还要看源表主键值分布情况和目标表的表结构，并不是所有多线程插入都能产生更好的效果节省时间，有时候反而可能多线程比单线程更耗时间以及资源。