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mysql 1280_技术分享 | MySQL 一次奇怪的故障分析

發布時間：2024/4/18 数据库 53 豆豆

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一、問題來源

這是一個朋友問我的典型案例。整個故障現象表現為，MySQL 數據庫頻繁的出現大量的請求不能響應。下面是一些他提供的證據：

1. show processlist從狀態信息來看出現如下情況：insert 操作：狀態為 update

update/delete 操作：狀態為 updating

select 操作：狀態為 sending data

因此可以推斷應該是語句執行期間出現了問題，由于篇幅原因只給出一部分，并且我將語句部分也做了相應截斷：show?processlist----------------------------......11827639????root????dbmis???Execute?9???updating????UPDATE17224594????root????dbmis???Execute?8???Sending?data????SELECT?sum(exchange_coin)?as?exchange_coin?FROM17224595????root????dbmis???Execute?8???update??INSERT?INTO17224596????root????dg??Execute?8???update??INSERT?INTO17224597????root????dbmis???Execute?8???update??INSERT?INTO17224598????root????dbmis???Execute?7???update??INSERT?INTO17224599????root????dbmis???Execute?7???Sending?data????SELECT?COUNT(*)?AS?tp_count?FROM17224600????root????dg??Execute?7???update??INSERT?INTO17224601????root????dbmis???Execute?6???update??INSERT?INTO17224602????root????dbmis???Execute?6???Sending?data????SELECT?sum(exchange_coin)?as?exchange_coin?FROM17224606????root????dbmis???Execute?5???update??INSERT?INTO17224619????root????dbmis???Execute?2???update??INSERT?INTO17224620????root????dbmis???Execute?2???update??INSERT?INTO17224621????root????dbmis???Execute?2???Sending?data????SELECT?sum(exchange_coin)?as?exchange_coin17224622????root????dg??Execute?2???update??INSERT?INTO17224623????root????dbmis???Execute?1???update??INSERT?INTO17224624????root????dbmis???Execute?1???update??INSERT?INTO17224625????root????dg??Execute?1???update??INSERT?INTO17224626????root????dbmis???Execute?0???update??INSERT?INTO

2. 系統 IO/CPU

從 vmstat 來看，CPU 使用不大，而 IO 也在可以接受的范圍內(vmstat wa% 不高且 b 列為 0 )如下：vmstat--------------------------------------

procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----

r ?b ? swpd ? free ? buff ?cache ? si ? so ? ?bi ? ?bo ? in ? cs us sy id wa st

2 ?0 927300 3057100 ? ? ?0 53487316 ? ?0 ? ?0 ? ? 5 ? 192 ? ?0 ? ?0 ?3 ?1 96 ?0 ?0

iostat--------------------------------------

Linux 3.10.0-693.el7.x86_64 (fang-data1) ? ? 09/23/2019 ?_x86_64_ ? ?(32 CPU)

avg-cpu: ?%user ? %nice %system %iowait ?%steal ? %idle

2.72 ? ?0.00 ? ?0.52 ? ?0.45 ? ?0.00 ? 96.31

Device: ? ? ? ? rrqm/s ? wrqm/s ? ? r/s ? ? w/s ? ?rkB/s ? ?wkB/s avgrq-sz avgqu-sz ? await r_await w_await ?svctm ?%util

sdb ? ? ? ? ? ? ? 9.73 ? ?11.28 ? ?3.93 ?264.54 ? 415.23 ?2624.20 ? ?22.64 ? ? 0.25 ? ?0.93 ? ?3.25 ? ?0.90 ? 0.80 ?21.61

sda ? ? ? ? ? ? ?10.13 ? ?11.59 ? ?6.34 ?264.22 ? 450.68 ?2624.20 ? ?22.73 ? ? 0.01 ? ?0.05 ? ?2.55 ? ?1.00 ? 0.93 ?25.19

sdc ? ? ? ? ? ? ?11.60 ? ?11.36 ? ?5.03 ?263.12 ? 453.02 ?2592.44 ? ?22.71 ? ? 0.17 ? ?0.62 ? ?5.08 ? ?0.53 ? 0.81 ?21.60

sde ? ? ? ? ? ? ? 0.01 ? ? 0.10 ? ?0.11 ?160.45 ? ? 6.69 ? 920.23 ? ?11.55 ? ? 0.16 ? ?1.01 ? ?1.80 ? ?1.01 ? 0.83 ?13.32

sdd ? ? ? ? ? ? ?11.26 ? ?11.30 ? ?2.23 ?263.18 ? 412.90 ?2592.44 ? ?22.65 ? ? 0.17 ? ?0.65 ? 10.37 ? ?0.56 ? 0.82 ?21.78

md126 ? ? ? ? ? ? 0.00 ? ? 0.00 ? 11.30 ?468.80 ? 164.79 ?5216.64 ? ?22.42 ? ? 0.00 ? ?0.00 ? ?0.00 ? ?0.00 ? 0.00 ? 0.00

dm-0 ? ? ? ? ? ? ?0.00 ? ? 0.00 ? ?0.11 ? 58.80 ? ? 6.69 ? 920.23 ? ?31.47 ? ? 0.15 ? ?2.56 ? ?1.96 ? ?2.56 ? 2.16 ?12.74

dm-1 ? ? ? ? ? ? ?0.00 ? ? 0.00 ? ?0.06 ? ?0.08 ? ? 0.24 ? ? 0.31 ? ? 8.00 ? ? 0.01 ? 41.80 ? ?1.20 ? 72.78 ? 0.83 ? 0.01

dm-2 ? ? ? ? ? ? ?0.00 ? ? 0.00 ? 11.24 ?408.66 ? 164.55 ?5216.33 ? ?25.63 ? ? 0.14 ? ?0.32 ? ?1.02 ? ?0.30 ? 0.46 ?19.29

這就比較奇怪了，一般來說數據庫不能及時響應請求很大可能是由于系統負載過高。如果說 DML 還可能是 Innodb 鎖造成的堵塞，但是大量 sending data 狀態下的 select 操作一般可能都和系統負載過高有聯系，但是這里系統負載還在可以接受的范圍內。

二、pstack 分析借助 pstack 查看線程的棧幀，查看 pstack 發現如下(由于篇幅限制只給出部分說明問題的部分)：

1. insert 線程：Thread?85?(Thread?0x7fbb0d42b700?(LWP?20174)):#0??0x00007fbfae164c73?in?select?()?from?/lib64/libc.so.6#1??0x0000000000987c0f?in?os_thread_sleep?(tm=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/os/os0thread.cc:287#2??0x00000000009e4dea?in?srv_conc_enter_innodb_with_atomics?(trx=trx@entry=0x7fba4802f9c8)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:276#3??srv_conc_enter_innodb?(trx=trx@entry=0x7fba4802f9c8)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:511#4??0x000000000093b948?in?innobase_srv_conc_enter_innodb?(trx=0x7fba4802f9c8)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:1280#5??ha_innobase::write_row?(this=0x7fb8440ab260,?record=0x7fb8440ab650?"")?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:6793#6??0x00000000005b440f?in?handler::ha_write_row?(this=0x7fb8440ab260,?buf=0x7fb8440ab650?"")?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:7351#7??0x00000000006dd3a8?in?write_record?(thd=thd@entry=0x1d396c90,?table=table@entry=0x7fb8440aa970,?info=info@entry=0x7fbb0d429400,?update=update@entry=0x7fbb0d429480)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_insert.cc:1667#8??0x00000000006e2541?in?mysql_insert?(thd=thd@entry=0x1d396c90,?table_list=,?fields=...,?values_list=...,?update_fields=...,?update_values=...,?duplic=DUP_REPLACE,?ignore=false)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_insert.cc:1072#9??0x00000000006fa90a?in?mysql_execute_command?(thd=thd@entry=0x1d396c90)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_parse.cc:3500

2. update 線程Thread?81?(Thread?0x7fbb24b67700?(LWP?27490)):#0??0x00007fbfae164c73?in?select?()?from?/lib64/libc.so.6#1??0x0000000000987c0f?in?os_thread_sleep?(tm=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/os/os0thread.cc:287#2??0x00000000009e4dea?in?srv_conc_enter_innodb_with_atomics?(trx=trx@entry=0x7fb94003c608)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:276#3??srv_conc_enter_innodb?(trx=trx@entry=0x7fb94003c608)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:511#4??0x000000000093ae4e?in?innobase_srv_conc_enter_innodb?(trx=0x7fb94003c608)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:1280#5??ha_innobase::index_read?(this=0x7fb95c05b540,?buf=0x7fb95c2ae4f0?"\377\377\377",?key_ptr=,?key_len=,?find_flag=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:7675#6??0x00000000005ab6e0?in?ha_index_read_map?(find_flag=HA_READ_KEY_EXACT,?keypart_map=3,?key=0x7fb940017048?"7\307\017e\257h",?buf=,?this=0x7fb95c05b540)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:2753#7??handler::read_range_first?(this=0x7fb95c05b540,?start_key=,?end_key=,?eq_range_arg=,?sorted=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:6717#8??0x00000000005aa206?in?handler::multi_range_read_next?(this=0x7fb95c05b540,?range_info=0x7fbb24b65240)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:5871#9??0x0000000000804acb?in?QUICK_RANGE_SELECT::get_next?(this=0x7fb94000f720)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/opt_range.cc:10644#10?0x000000000082ae2d?in?rr_quick?(info=0x7fbb24b65410)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/records.cc:369#11?0x0000000000766e1b?in?mysql_update?(thd=thd@entry=0x1d1f2250,?table_list=,?fields=...,?values=...,?conds=0x7fb9400009c8,?order_num=,?order=,?limit=18446744073709551615,?handle_duplicates=DUP_ERROR,?ignore=false,?found_return=found_return@entry=0x7fbb24b65800,?updated_return=updated_return@entry=0x7fbb24b65d60)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_update.cc:744

3. select 線程Thread?66?(Thread?0x7fbb3c355700?(LWP?16028)):#0??0x00007fbfae164c73?in?select?()?from?/lib64/libc.so.6#1??0x0000000000987c0f?in?os_thread_sleep?(tm=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/os/os0thread.cc:287#2??0x00000000009e4dea?in?srv_conc_enter_innodb_with_atomics?(trx=trx@entry=0x7fb988354858)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:276#3??srv_conc_enter_innodb?(trx=trx@entry=0x7fb988354858)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/srv/srv0conc.cc:511#4??0x000000000093ae4e?in?innobase_srv_conc_enter_innodb?(trx=0x7fb988354858)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:1280#5??ha_innobase::index_read?(this=0x7fb9880e33a0,?buf=0x7fb988351b50?"\377\377\377\377",?key_ptr=,?key_len=,?find_flag=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/storage/innobase/handler/ha_innodb.cc:7675#6??0x00000000005ab6e0?in?ha_index_read_map?(find_flag=HA_READ_AFTER_KEY,?keypart_map=7,?key=0x7fb988134a48?"",?buf=,?this=0x7fb9880e33a0)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:2753#7??handler::read_range_first?(this=0x7fb9880e33a0,?start_key=,?end_key=,?eq_range_arg=,?sorted=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:6717#8??0x00000000005aa206?in?handler::multi_range_read_next?(this=0x7fb9880e33a0,?range_info=0x7fbb3c353400)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/handler.cc:5871#9??0x0000000000804acb?in?QUICK_RANGE_SELECT::get_next?(this=0x7fb988002050)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/opt_range.cc:10644#10?0x000000000082ae2d?in?rr_quick?(info=0x7fb98809c210)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/records.cc:369#11?0x00000000006d44fd?in?sub_select?(join=0x7fb98809a728,?join_tab=0x7fb98809c180,?end_of_records=)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_executor.cc:1259#12?0x00000000006d2823?in?do_select?(join=0x7fb98809a728)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_executor.cc:936#13?JOIN::exec?(this=0x7fb98809a728)?at?/home/install/lnmp1.5/src/mysql-5.6.40/sql/sql_executor.cc:194

好了有了這些棧幀視乎發現一些共同點他們都處于 innobase_srv_conc_enter_innodb 函數下，本函數正是下面參數實現的方式：innodb_thread_concurrency

innodb_concurrency_tickets

所以我隨即告訴他檢查這兩個參數，如果設置了可以嘗試取消。過后數據庫故障得到解決。

三、參數和相關說明實際上涉及到的參數主要是 innodb_thread_concurrency 和 innodb_concurrency_tickets。將高壓力下線程之間搶占 CPU 而造成線程上下文切換的情況盡量阻塞在 Innodb 層之外，這就需要 innodb_thread_concurrency 參數了。同時又要保證對于那些(長時間處理線程)不會長時間的堵塞(短時間處理線程)，比如某些 select 操作需要查詢很久，而某些 select 操作查詢量很小，如果等待(長時間的 select 操作)結束后(短時間 select 操作)才執行，那么顯然會出現(短時間 select 操作)饑餓問題，換句話說對(短時間 select 操作)是不公平的，因此就引入了 innodb_concurrency_tickets 參數。

1. innodb_thread_concurrency

同一時刻能夠進入 Innodb 層的會話(線程)數。如果在 Innodb 層干活的會話(線程)數量超過這個參數的設置，新會話(線程)將不能從 MySQL 層進入到 Innodb 層，它們將進入一個短暫的睡眠狀態。休眠多久則通過參數 innodb_thread_sleep_delay 參數指定，如果還設置了參數 innodb_adaptive_max_sleep_delay 那么 Innodb 將會自動調整休眠時間，具體的算法實際上就在 srv_conc_enter_innodb_with_atomics 函數中，感興趣的可以執行查看。其次這種休眠實際上是一個定時醒來的時鐘，通過 ::nanosleep 或者 select(多路 IO 轉接函數)進行實現，定時喚醒后會話(線程)重新判斷是否可以進入 Innodb 層。函數 os_thread_sleep 部分如下：#elif defined(HAVE_NANOSLEEP)

struct timespec t;

t.tv_sec = tm / 1000000;

t.tv_nsec = (tm % 1000000) * 1000;

::nanosleep(&t, NULL);

#else

struct timeval ?t;

t.tv_sec = tm / 1000000;

t.tv_usec = tm % 1000000;

select(0, NULL, NULL, NULL, &t);

關于到底如何設置這個值，官方文檔有如下建議：Use?the?following?guidelines?to?help?find?and?maintain?an?appropriate?setting:-?If?the?number?of?concurrent?user?threads?for?a?workload?is?less?than?64,?setinnodb_thread_concurrency=0.-?If?your?workload?is?consistently?heavy?or?occasionally?spikes,?start?by?settinginnodb_thread_concurrency=128?and?then?lowering?the?value?to?96,?80,?64,?and?so?on,?untilyou?find?the?number?of?threads?that?provides?the?best?performance.?For?example,?suppose?yoursystem?typically?has?40?to?50?users,?but?periodically?the?number?increases?to?60,?70,?or?even?200.You?find?that?performance?is?stable?at?80?concurrent?users?but?starts?to?show?a?regression?abovethis?number.?In?this?case,?you?would?set?innodb_thread_concurrency=80?to?avoid?impactingperformance.-?If?you?do?not?want?InnoDB?to?use?more?than?a?certain?number?of?virtual?CPUs?for?user?threads(20?virtual?CPUs,?for?example),?set?innodb_thread_concurrency?to?this?number?(or?possiblylower,?depending?on?performance?results).?If?your?goal?is?to?isolate?MySQL?from?other?applications,you?may?consider?binding?the?mysqld?process?exclusively?to?the?virtual?CPUs.?Be?aware,however,?that?exclusive?binding?could?result?in?non-optimal?hardware?usage?if?the?mysqld?processis?not?consistently?busy.?In?this?case,?you?might?bind?the?mysqld?process?to?the?virtual?CPUs?butalso?allow?other?applications?to?use?some?or?all?of?the?virtual?CPUs.-?innodb_thread_concurrency?values?that?are?too?high?can?cause?performance?regression?dueto?increased?contention?on?system?internals?and?resources.-?In?some?cases,?the?optimal?innodb_thread_concurrency?setting?can?be?smaller?than?thenumber?of?virtual?CPUs.-?Monitor?and?analyze?your?system?regularly.?Changes?to?workload,?number?of?users,?or?computingenvironment?may?require?that?you?adjust?the?innodb_thread_concurrency?setting

可以發現要合理的設置這個值并不那么容易并且要求較高。

2. innodb_concurrency_tickets實際上這里的 tickets 可以理解為 MySQL 層和 Innodb 層交互的次數，比如一個 select 一條數據就是需要 Innodb 層返回一條數據然后 MySQL 層進行 where 條件的過濾然后返回給客戶端，拋開 where 條件過濾的情況，如果我們一條語句需要查詢 100 條數據，那么實際上需要進入 Innodb 層 100 次，那么實際上消耗的 tickets 就是 100。當然對于 insert select 這種操作，需要的 tickets 是普通 select 的兩倍，因為查詢需要進入 Innodb 層一次，insert 需要再次進入 Innodb 層一次，后面我們就使用 insert select 的方式來模擬堵塞的情況，最后還會給出說明。這樣我們也就理解為什么 innodb_concurrency_tickets 可以避免(長時間處理線程)長時間堵塞(短時間處理線程)的原因了。假設 innodb_concurrency_tickets 為 5000(默認值)，有一個需要查詢 100W 行數據的大 select 操作和一個需要查詢 100 行數據的小 select 操作，大 select 操作先進行，但是當查詢了 5000 行數據后將丟失CPU使用權，小 select 操作將會進行并且一次性完成。最后關于這里涉及的參數可以繼續參考官方文檔中的說明，我們線上并沒有設置這些參數，因為感覺很難設置合適，如果設置不當反而會遇到問題，就如本案例一樣。

3. 事務操作狀態

實際上如果是處于這種堵塞情況，我們完全可以在 information_schema.innodb_trx 和 show engine innodb status 中看到如下：---TRANSACTION 162307, ACTIVE 133 sec sleeping before entering InnoDB (這里)

mysql tables in use 2, locked 2

767 lock struct(s), heap size 106968, 212591 row lock(s), undo log entries 15451

MySQL thread id 14, OS thread handle 140736751912704, query id 1077 localhost root Sending data

insert into testui select * from testui

---TRANSACTION 162302, ACTIVE 320 sec, thread declared inside InnoDB 1

mysql tables in use 2, locked 2

2477 lock struct(s), heap size 336344, 609049 row lock(s), undo log entries 83582

MySQL thread id 13, OS thread handle 140737153779456, query id 1050 localhost root Sending data

insert into testti3 select * from testti3

mysql> select trx_id,trx_state,trx_query,trx_operation_state,trx_concurrency_tickets from information_schema.innodb_trx \G

*************************** 1. row ***************************

trx_id: 84325

trx_state: RUNNING

trx_query: insert into ?baguait4 select * from testgp

trx_operation_state: sleeping before entering InnoDB(這里)

trx_concurrency_tickets: 0

*************************** 2. row ***************************

trx_id: 84319

trx_state: RUNNING

trx_query: insert into ?baguait3 select * from testgp

trx_operation_state: sleeping before entering InnoDB

trx_concurrency_tickets: 0

我們可以看到事務操作狀態被標記為sleeping before entering InnoDB。但是需要注意一點的是對于只讀事務比如 select 操作而言，show engine innodb status 可能看不到。但是遺憾的是案例中朋友并沒有采集 trx_operation_state 的值。

四、模擬測試這里我們簡單模擬，我們一共啟用3個事務，其中兩個 insert select 操作，一個單純的 select 操作，當然這里的都是耗時操作，涉及的表每個表都有大概 100W 的數據。

同時為了方便觀察我們需要設置參數：innodb_thread_concurrency=1

innodb_concurrency_tickets=10

操作步驟如下：

如果多觀察幾次你可以看到如下的現象：mysql> select trx_id,trx_state,trx_query,trx_operation_state,trx_concurrency_tickets from information_schema.innodb_trx \G show processlist;

*************************** 1. row ***************************

trx_id: 84529

trx_state: RUNNING

trx_query: insert into ?baguait4 select * from testgp

trx_operation_state: sleeping before entering InnoDB

trx_concurrency_tickets: 0

*************************** 2. row ***************************

trx_id: 84524

trx_state: RUNNING

trx_query: insert into ?baguait3 select * from testgp

trx_operation_state: inserting

trx_concurrency_tickets: 1

*************************** 3. row ***************************

trx_id: 422211785606640

trx_state: RUNNING

trx_query: select * from baguait1

trx_operation_state: sleeping before entering InnoDB

trx_concurrency_tickets: 0

3 rows in set (0.00 sec)

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

5 rows in set (0.00 sec)

mysql>

mysql> select trx_id,trx_state,trx_query,trx_operation_state,trx_concurrency_tickets from information_schema.innodb_trx \G show processlist;

*************************** 1. row ***************************

trx_id: 84529

trx_state: RUNNING

trx_query: insert into ?baguait4 select * from testgp

trx_operation_state: sleeping before entering InnoDB

trx_concurrency_tickets: 0

*************************** 2. row ***************************

trx_id: 84524

trx_state: RUNNING

trx_query: insert into ?baguait3 select * from testgp

trx_operation_state: sleeping before entering InnoDB

trx_concurrency_tickets: 0

*************************** 3. row ***************************

trx_id: 422211785606640

trx_state: RUNNING

trx_query: select * from baguait1

trx_operation_state: fetching rows

trx_concurrency_tickets: 3

3 rows in set (0.00 sec)

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

+----+-----------------+-----------+---------+---------+------+------------------------+--------------------------------------------+-----------+---------------+

5 rows in set (0.00 sec)

我們可以觀察到 trx_operation_state 的狀態 3 個操作都在交替的變化，但是總有 2 個處于sleeping before entering InnoDB狀態。并且我們可以觀察到 trx_concurrency_tickets 總是不會大于 10 的。因此我們有理由相信在同一時刻只有一個操作進入了 Innodb 層。但是需要注意的是在 show engine innodb status 中觀察不到 select 的操作如下：------------TRANSACTIONS------------Trx?id?counter?84538Purge?done?for?trx's?n:o?=?84529,?sees?=?84524,?sees?

但是我們還需要注意 show engine innodb status 有如下輸出第一行說明了有 2 個會話(線程)堵塞在 Innodb 層以外。--------------ROW?OPERATIONS--------------1?queries?inside?InnoDB,?2?queries?in?queue3?read?views?open?inside?InnoDB2?RW?transactions?active?inside?InnoDB

五、實現方法前面我們已經描述了每次 MySQL 層和 Innodb 層的交互都會進行一次這樣的判斷，它用來決定會話(線程)是否能夠進入 Innodb 層，下面就是大概的邏輯，由函數 innobase_srv_conc_enter_innodb 調入。->是否設置了參數innodb_thread_concurrency??->是?????->是否tickets大于0????????->是、直接進入Innodb層并且tickets減1????????->否、調入函數srv_conc_enter_innodb???????????->調入函數srv_conc_enter_innodb_with_atomics??????????????->開啟死循環?????????????????->是否活躍線程數小于innodb_thread_concurrency設置????????????????????->是、增加活躍線程數，并且自動調整delay參數，退出死循環，滿tickets進入Innodb層????????????????????->否、自動調整delay參數后設置事務操作狀態為"sleeping?before?entering?InnoDB"，然后進入休眠狀態直到時間達到后重新醒來繼續循環??->否、直接進入Innodb層

我們可以看到這個實現方式，在 Inndob 以外的會話(線程)會一直等待直到 Inndob 層內活躍的線程數小于 innodb_thread_concurrency 為止，并且每次進入 Innodb 層都會將 tickets 減 1。

其他：關于 insert select 操作消耗 tickets 的說明這里額外說明一下，因為我在測試的時候看了一下，對于一行數據而言首先需要 select 查詢出來然后再 insert 插入到表中，這里實際上一行數據涉及到進入 Innodb 層兩次，那么就需要消耗 2 個 tickets，下面留下兩個棧幀供自己后面參考：

1. insert select 查詢數據進入 Innodb 層#0??innobase_srv_conc_enter_innodb?(prebuilt=0x7ffedcb98d10)?at?/mysqldata/percona-server-locks-detail-5.7.22/storage/innobase/handler/ha_innodb.cc:1740#1??0x0000000001a53f7c?in?ha_innobase::general_fetch?(this=0x7ffedcb9d760,?buf=0x7ffedc9469b0?"\375\n",?direction=1,?match_mode=0)????at?/mysqldata/percona-server-locks-detail-5.7.22/storage/innobase/handler/ha_innodb.cc:9846#2??0x0000000001a545ee?in?ha_innobase::rnd_next?(this=0x7ffedcb9d760,?buf=0x7ffedc9469b0?"\375\n")????at?/mysqldata/percona-server-locks-detail-5.7.22/storage/innobase/handler/ha_innodb.cc:10083#3??0x0000000000f836d6?in?handler::ha_rnd_next?(this=0x7ffedcb9d760,?buf=0x7ffedc9469b0?"\375\n")?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/handler.cc:3146#4??0x00000000014e2a55?in?rr_sequential?(info=0x7ffedcb4f120)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/records.cc:521#5??0x0000000001581277?in?sub_select?(join=0x7ffedcb4ea20,?qep_tab=0x7ffedcb4f0d0,?end_of_records=false)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:1280#6??0x0000000001580be6?in?do_select?(join=0x7ffedcb4ea20)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:950#7??0x000000000157eaa2?in?JOIN::exec?(this=0x7ffedcb4ea20)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:199#8??0x0000000001620327?in?handle_query?(thd=0x7ffedc012960,?lex=0x7ffedc014f90,?result=0x7ffedcc46680,?added_options=1342177280,?removed_options=0)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_select.cc:185#9??0x000000000180466d?in?Sql_cmd_insert_select::execute?(this=0x7ffedcc46608,?thd=0x7ffedc012960)

2. insert select 插入數據進入 Innodb 層#0??innobase_srv_conc_enter_innodb?(prebuilt=0x7ffedcb9c6f0)?at?/mysqldata/percona-server-locks-detail-5.7.22/storage/innobase/handler/ha_innodb.cc:1740#1??0x0000000001a50587?in?ha_innobase::write_row?(this=0x7ffedc946470,?record=0x7ffedcb78d00?"\375\n")????at?/mysqldata/percona-server-locks-detail-5.7.22/storage/innobase/handler/ha_innodb.cc:8341#2??0x0000000000f9041d?in?handler::ha_write_row?(this=0x7ffedc946470,?buf=0x7ffedcb78d00?"\375\n")?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/handler.cc:8466#3??0x00000000018004b9?in?write_record?(thd=0x7ffedc012960,?table=0x7ffedcb8f940,?info=0x7ffedcc466c8,?update=0x7ffedcc46740)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_insert.cc:1881#4??0x00000000018019b9?in?Query_result_insert::send_data?(this=0x7ffedcc46680,?values=...)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_insert.cc:2279#5??0x00000000015853a8?in?end_send?(join=0x7ffedcb4ea20,?qep_tab=0x7ffedcb4f248,?end_of_records=false)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:2925#6??0x0000000001581f71?in?evaluate_join_record?(join=0x7ffedcb4ea20,?qep_tab=0x7ffedcb4f0d0)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:1645#7??0x0000000001581372?in?sub_select?(join=0x7ffedcb4ea20,?qep_tab=0x7ffedcb4f0d0,?end_of_records=false)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:1297#8??0x0000000001580be6?in?do_select?(join=0x7ffedcb4ea20)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:950#9??0x000000000157eaa2?in?JOIN::exec?(this=0x7ffedcb4ea20)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:199#10?0x0000000001620327?in?handle_query?(thd=0x7ffedc012960,?lex=0x7ffedc014f90,?result=0x7ffedcc46680,?added_options=1342177280,?removed_options=0)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_select.cc:185#11?0x000000000180466d?in?Sql_cmd_insert_select::execute?(this=0x7ffedcc46608,?thd=0x7ffedc012960)

實際上插入數據正是在查詢完數據后調用函數 evaluate_join_record 的時候，通過回調了函數 Query_result_insert::send_data 來實現，這點和單純的 select 不一樣單純的 select 這里調入是函數 Query_result_send::send_data 如下：#0??Query_result_send::send_data?(this=0x7ffedcc465f8,?items=...)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_class.cc:2915#1??0x00000000015853a8?in?end_send?(join=0x7ffedcb4e930,?qep_tab=0x7ffedcb4f4b0,?end_of_records=false)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:2925#2??0x0000000001581f71?in?evaluate_join_record?(join=0x7ffedcb4e930,?qep_tab=0x7ffedcb4f338)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:1645#3??0x0000000001581372?in?sub_select?(join=0x7ffedcb4e930,?qep_tab=0x7ffedcb4f338,?end_of_records=false)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:1297#4??0x0000000001580be6?in?do_select?(join=0x7ffedcb4e930)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:950#5??0x000000000157eaa2?in?JOIN::exec?(this=0x7ffedcb4e930)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_executor.cc:199#6??0x0000000001620327?in?handle_query?(thd=0x7ffedc012960,?lex=0x7ffedc014f90,?result=0x7ffedcc465f8,?added_options=0,?removed_options=0)????at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_select.cc:185#7??0x00000000015d1f77?in?execute_sqlcom_select?(thd=0x7ffedc012960,?all_tables=0x7ffedcc45cf0)?at?/mysqldata/percona-server-locks-detail-5.7.22/sql/sql_parse.cc:5445

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