PostgreSQL的学习心得和知识总结（一百四十五）|深入理解PostgreSQL数据库之ShowTransactionState的使用及父子事务有限状态机

目录结构

注：提前言明本文借鉴了以下博主、书籍或网站的内容，其列表如下：

1、参考书籍：《PostgreSQL数据库内核分析》
2、参考书籍：《数据库事务处理的艺术：事务管理与并发控制》
3、PostgreSQL数据库仓库链接，点击前往
4、日本著名PostgreSQL数据库专家铃木启修网站主页，点击前往
5、参考书籍：《PostgreSQL中文手册》
6、参考书籍：《PostgreSQL指南：内幕探索》，点击前往

1、本文内容全部来源于开源社区 GitHub和以上博主的贡献，本文也免费开源（可能会存在问题，评论区等待大佬们的指正）
2、本文目的：开源共享抛砖引玉一起学习
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5、本文内容基于PostgreSQL master源码开发而成

深入理解PostgreSQL数据库之ShowTransactionState的使用及父子事务有限状态机

文章快速说明索引
重点数据结构说明
源码解析案例分解
- INFO0
- INFO1
- INFO2
- INFO3
- INFO4
- INFO5
- INFO6
- INFO7
- INFO8
- INFO9

文章快速说明索引

学习目标：

做数据库内核开发久了就会有一种少年得志，年少轻狂的错觉，然鹅细细一品觉得自己其实不算特别优秀远远没有达到自己想要的。也许光鲜的表面掩盖了空洞的内在，每每想到于此，皆有夜半临渊如履薄冰之感。为了睡上几个踏实觉，即日起暂缓其他基于PostgreSQL数据库的兼容功能开发，近段时间将着重于学习分享Postgres的基础知识和实践内幕。

学习内容：（详见目录）

1、深入理解PostgreSQL数据库之ShowTransactionState的使用及父子事务有限状态机

学习时间：

2024年06月02日 21:22:11

学习产出：

1、PostgreSQL数据库基础知识回顾 1个
2、CSDN 技术博客 1篇
3、PostgreSQL数据库内核深入学习

注：下面我们所有的学习环境是Centos8+PostgreSQL master+Oracle19C+MySQL8.0

postgres=# select version();version                                                   
------------------------------------------------------------------------------------------------------------PostgreSQL 17devel on x86_64-pc-linux-gnu, compiled by gcc (GCC) 8.5.0 20210514 (Red Hat 8.5.0-21), 64-bit
(1 row)postgres=##-----------------------------------------------------------------------------#SQL> select * from v$version;          BANNER        Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production	
BANNER_FULL	  Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production Version 19.17.0.0.0	
BANNER_LEGACY Oracle Database 19c EE Extreme Perf Release 19.0.0.0.0 - Production	
CON_ID 0#-----------------------------------------------------------------------------#mysql> select version();
+-----------+
| version() |
+-----------+
| 8.0.27    |
+-----------+
1 row in set (0.06 sec)mysql>

重点数据结构说明

// src/backend/access/transam/xact.c/**	transaction states - transaction state from server perspective*	事务状态 - 从服务器角度的事务状态*/
typedef enum TransState
{TRANS_DEFAULT,				/* idle */TRANS_START,				/* transaction starting */TRANS_INPROGRESS,			/* inside a valid transaction */TRANS_COMMIT,				/* commit in progress */TRANS_ABORT,				/* abort in progress */TRANS_PREPARE,				/* prepare in progress */
} TransState;/**	transaction block states - transaction state of client queries*	事务块状态 - 客户端查询的事务状态** Note: the subtransaction states are used only for non-topmost* transactions; the others appear only in the topmost transaction.* 注意：子事务(subtransaction)状态仅用于非最顶层事务；其他状态仅出现在最顶层事务中。*/
typedef enum TBlockState
{/* not-in-transaction-block states */TBLOCK_DEFAULT,				/* idle */TBLOCK_STARTED,				/* running single-query transaction *//* transaction block states */TBLOCK_BEGIN,				/* starting transaction block */TBLOCK_INPROGRESS,			/* live transaction */TBLOCK_IMPLICIT_INPROGRESS, /* live transaction after implicit BEGIN */TBLOCK_PARALLEL_INPROGRESS, /* live transaction inside parallel worker */TBLOCK_END,					/* COMMIT received */TBLOCK_ABORT,				/* failed xact, awaiting ROLLBACK */TBLOCK_ABORT_END,			/* failed xact, ROLLBACK received */TBLOCK_ABORT_PENDING,		/* live xact, ROLLBACK received */TBLOCK_PREPARE,				/* live xact, PREPARE received *//* subtransaction states */TBLOCK_SUBBEGIN,			/* starting a subtransaction */TBLOCK_SUBINPROGRESS,		/* live subtransaction */TBLOCK_SUBRELEASE,			/* RELEASE received */TBLOCK_SUBCOMMIT,			/* COMMIT received while TBLOCK_SUBINPROGRESS */TBLOCK_SUBABORT,			/* failed subxact, awaiting ROLLBACK */TBLOCK_SUBABORT_END,		/* failed subxact, ROLLBACK received */TBLOCK_SUBABORT_PENDING,	/* live subxact, ROLLBACK received */TBLOCK_SUBRESTART,			/* live subxact, ROLLBACK TO received */TBLOCK_SUBABORT_RESTART,	/* failed subxact, ROLLBACK TO received */
} TBlockState;

首先我们看一下今天的重点函数ShowTransactionState的内部实现，如下：

/** ShowTransactionState*		Debug support*/
static void
ShowTransactionState(const char *str)
{/* skip work if message will definitely not be printed */if (message_level_is_interesting(DEBUG5))ShowTransactionStateRec(str, CurrentTransactionState);
}/** ShowTransactionStateRec*		Recursive subroutine for ShowTransactionState*		ShowTransactionState 的递归子程序*/
static void
ShowTransactionStateRec(const char *str, TransactionState s)
{StringInfoData buf;if (s->parent){/** Since this function recurses, it could be driven to stack overflow.* This is just a debugging aid, so we can leave out some details* instead of erroring out with check_stack_depth().*  * 由于此函数递归，可能会导致堆栈溢出* 这只是一个调试辅助工具，因此我们可以省略一些细节* 而不是使用 check_stack_depth() 出错*/if (stack_is_too_deep())ereport(DEBUG5,(errmsg_internal("%s(%d): parent omitted to avoid stack overflow",str, s->nestingLevel)));elseShowTransactionStateRec(str, s->parent);}initStringInfo(&buf);if (s->nChildXids > 0){int			i;appendStringInfo(&buf, ", children: %u", s->childXids[0]);for (i = 1; i < s->nChildXids; i++)appendStringInfo(&buf, " %u", s->childXids[i]);}ereport(DEBUG5,(errmsg_internal("%s(%d) name: %s; blockState: %s; state: %s, xid/subid/cid: %u/%u/%u%s%s",str, s->nestingLevel,PointerIsValid(s->name) ? s->name : "unnamed",BlockStateAsString(s->blockState),TransStateAsString(s->state),(unsigned int) XidFromFullTransactionId(s->fullTransactionId),(unsigned int) s->subTransactionId,(unsigned int) currentCommandId,currentCommandIdUsed ? " (used)" : "",buf.data)));pfree(buf.data);
}

我们对上面逻辑进行修改，patch如下：

[postgres@localhost:~/postgres → master]$ git diff src/backend/access/transam/xact.c
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 4f4ce75762..336b4d1ee7 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -5599,7 +5599,7 @@ static voidShowTransactionState(const char *str){/* skip work if message will definitely not be printed */
-       if (message_level_is_interesting(DEBUG5))
+       // if (message_level_is_interesting(DEBUG5))ShowTransactionStateRec(str, CurrentTransactionState);}@@ -5620,7 +5620,7 @@ ShowTransactionStateRec(const char *str, TransactionState s)* instead of erroring out with check_stack_depth().*/if (stack_is_too_deep())
-                       ereport(DEBUG5,
+                       ereport(INFO,(errmsg_internal("%s(%d): parent omitted to avoid stack overflow",str, s->nestingLevel)));else
@@ -5636,7 +5636,7 @@ ShowTransactionStateRec(const char *str, TransactionState s)for (i = 1; i < s->nChildXids; i++)appendStringInfo(&buf, " %u", s->childXids[i]);}
-       ereport(DEBUG5,
+       ereport(INFO,(errmsg_internal("%s(%d) name: %s; blockState: %s; state: %s, xid/subid/cid: %u/%u/%u%s%s",str, s->nestingLevel,PointerIsValid(s->name) ? s->name : "unnamed",
[postgres@localhost:~/postgres → master]$

源码解析案例分解

案例展示，如下：

-- INFO0
[postgres@localhost:~/test/bin]$ ./psql 
INFO:  CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 0/1/0
psql (17beta1)
Type "help" for help.-- INFO1
postgres=# create table t1 (id int);
INFO:  StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
INFO:  CommitTransaction(1) name: unnamed; blockState: STARTED; state: INPROGRESS, xid/subid/cid: 738/1/1
CREATE TABLE
-- INFO2
postgres=# begin;
INFO:  StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0
BEGIN
postgres=*# insert into t1 values(1);
INSERT 0 1
-- INFO3
postgres=*# savepoint sp1;
INFO:  StartSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/1
INFO:  StartSubTransaction(2) name: sp1; blockState: SUBBEGIN; state: INPROGRESS, xid/subid/cid: 0/2/1
SAVEPOINT
postgres=*# insert into t1 values(2);
INSERT 0 1
-- INFO4
postgres=*# savepoint sp2;
INFO:  StartSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/2
INFO:  StartSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/2
INFO:  StartSubTransaction(3) name: sp2; blockState: SUBBEGIN; state: INPROGRESS, xid/subid/cid: 0/3/2
SAVEPOINT
postgres=*# insert into t1 values(3);
INSERT 0 1
-- INFO5
postgres=*# savepoint sp3;
INFO:  StartSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/3
INFO:  StartSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/3
INFO:  StartSubTransaction(3) name: sp2; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 741/3/3
INFO:  StartSubTransaction(4) name: sp3; blockState: SUBBEGIN; state: INPROGRESS, xid/subid/cid: 0/4/3
SAVEPOINT
postgres=*# select * from t1;id 
----123
(3 rows)postgres=*# insert into t1 values(4);
INSERT 0 1
-- INFO6
postgres=*# release savepoint sp2;
INFO:  CommitSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/4
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/4
INFO:  CommitSubTransaction(3) name: sp2; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 741/3/4
INFO:  CommitSubTransaction(4) name: sp3; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 742/4/4
INFO:  CommitSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/4
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/4
INFO:  CommitSubTransaction(3) name: sp2; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 741/3/4, children: 742
RELEASE
postgres=*# select * from t1;id 
----1234
(4 rows)-- INFO7
postgres=*# savepoint sp1;
INFO:  StartSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/4
INFO:  StartSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/4, children: 741 742
INFO:  StartSubTransaction(3) name: sp1; blockState: SUBBEGIN; state: INPROGRESS, xid/subid/cid: 0/5/4
SAVEPOINT
postgres=*# insert into t1 values(5);
INSERT 0 1
-- INFO8
postgres=*# rollback to savepoint sp1;
INFO:  AbortSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  AbortSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 741 742
INFO:  AbortSubTransaction(3) name: unnamed; blockState: SUBRESTART; state: INPROGRESS, xid/subid/cid: 743/5/5
INFO:  CleanupSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CleanupSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 741 742
INFO:  CleanupSubTransaction(3) name: unnamed; blockState: SUBRESTART; state: ABORT, xid/subid/cid: 743/5/5
INFO:  StartSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  StartSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 741 742
INFO:  StartSubTransaction(3) name: sp1; blockState: SUBBEGIN; state: INPROGRESS, xid/subid/cid: 0/6/5
ROLLBACK
postgres=*# select * from t1;id 
----1234
(4 rows)-- INFO9
postgres=*# end;
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 741 742
INFO:  CommitSubTransaction(3) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 0/6/5
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 741 742
INFO:  CommitTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5, children: 740 741 742
COMMIT
postgres=#

接下来，我们对上面这10个info块逐个进行分析，如下：

INFO0

..."setupCommands": [{"description": "为 gdb 启用整齐打印","text": "-enable-pretty-printing","ignoreFailures": true},{"description": "将反汇编风格设置为 Intel","text": "-gdb-set disassembly-flavor intel","ignoreFailures": true},{"text": "-gdb-set follow-fork-mode child"} ## here]
...

在这里插入图片描述

此时的堆栈，如下：

ShowTransactionStateRec(const char * str, TransactionState s)
ShowTransactionState(const char * str)
StartTransactionCommand()
InitPostgres(const char * in_dbname, Oid dboid, const char * username, Oid useroid, bits32 flags, char * out_dbname)
PostgresMain(const char * dbname, const char * username)
BackendMain(char * startup_data, size_t startup_data_len)
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock)
BackendStartup(ClientSocket * client_sock)
ServerLoop()
PostmasterMain(int argc, char ** argv)
main(int argc, char ** argv)

-- 这里实际上会打印下面这样一行
-- 没有打印的原因：现在正在建立连接的初始状态中 尚无法往client发送INFO:  StartTransaction(1) name: unnamed; blockState: DEFAULT; state: INPROGRESS, xid/subid/cid: 0/1/0

在这里插入图片描述

## 该过程中，相关状态机的变化：state的值改变：TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS## StartTransaction() 之后
blockState的值改变：TBLOCK_DEFAULT -> TBLOCK_STARTED## 继续：

## 此时的函数堆栈，如下：ShowTransactionStateRec(const char * str, TransactionState s)
ShowTransactionState(const char * str)
CommitTransaction()
CommitTransactionCommandInternal()
CommitTransactionCommand()
InitPostgres(const char * in_dbname, Oid dboid, const char * username, Oid useroid, bits32 flags, char * out_dbname)
PostgresMain(const char * dbname, const char * username)
BackendMain(char * startup_data, size_t startup_data_len)
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock)
BackendStartup(ClientSocket * client_sock)
ServerLoop()
PostmasterMain(int argc, char ** argv)
main(int argc, char ** argv)

在这里插入图片描述

## 上面INFO打印之后，相关状态机的变化：state的值改变：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT## CommitTransaction() 之后
blockState的值改变：TBLOCK_STARTED -> TBLOCK_DEFAULT## INFO0结束！

接下来我们调试的将不再是附加postmaster进程，而是上面这个backend进程！

INFO1

此时函数堆栈，如下：

ShowTransactionStateRec(const char * str, TransactionState s)
ShowTransactionState(const char * str)
StartTransaction()
StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string) ## here
PostgresMain(const char * dbname, const char * username)
BackendMain(char * startup_data, size_t startup_data_len)
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock)
BackendStartup(ClientSocket * client_sock)
ServerLoop()
PostmasterMain(int argc, char ** argv)
main(int argc, char ** argv)

在这里插入图片描述

## 该过程中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS## StartTransaction() 之后：
blockState的值改变： TBLOCK_DEFAULT->TBLOCK_STARTED## 继续

接下来是执行这个create语句！

## 函数堆栈，如下：ShowTransactionStateRec(const char * str, TransactionState s)
ShowTransactionState(const char * str)
CommitTransaction()
CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command() ## here
exec_simple_query(const char * query_string)
PostgresMain(const char * dbname, const char * username)
BackendMain(char * startup_data, size_t startup_data_len)
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock)
BackendStartup(ClientSocket * client_sock)
ServerLoop()
PostmasterMain(int argc, char ** argv)
main(int argc, char ** argv)

在这里插入图片描述

## 上面INFO打印之后，相关状态机的变化：State的值改变： TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT## CommitTransaction() 之后：
blockState的值改变： TBLOCK_STARTED -> TBLOCK_DEFAULT## INFO1结束！

INFO2

此时的函数堆栈，如下：

ShowTransactionStateRec(const char * str, TransactionState s)
ShowTransactionState(const char * str)
StartTransaction() 
StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)  ## here 
PostgresMain(const char * dbname, const char * username) 
BackendMain(char * startup_data, size_t startup_data_len) 
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock) 
BackendStartup(ClientSocket * client_sock) 
ServerLoop() 
PostmasterMain(int argc, char ** argv) 
main(int argc, char ** argv)

在这里插入图片描述

## 该过程中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS## StartTransaction() 之后：
blockState的值改变： TBLOCK_DEFAULT -> TBLOCK_STARTED## 继续

接下来就是执行这个begin命令，再接下来的函数堆栈，如下：

BeginTransactionBlock()
standard_ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc) 
ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc) 
PortalRunUtility(Portal portal, PlannedStmt * pstmt, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, QueryCompletion * qc) 
PortalRunMulti(Portal portal, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
PortalRun(Portal portal, long count, _Bool isTopLevel, _Bool run_once, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc) ## here
exec_simple_query(const char * query_string)
...

# 在 BeginTransactionBlock() 中blockState的值改变： TBLOCK_STARTED -> TBLOCK_BEGIN

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) ## here
PostgresMain(const char * dbname, const char * username)
BackendMain(char * startup_data, size_t startup_data_len)
postmaster_child_launch(BackendType child_type, char * startup_data, size_t startup_data_len, ClientSocket * client_sock)
BackendStartup(ClientSocket * client_sock)
ServerLoop()
PostmasterMain(int argc, char ** argv)
main(int argc, char ** argv)

## 在 CommitTransactionCommandInternal() 中blockState的值改变： TBLOCK_BEGIN -> TBLOCK_INPROGRESS

接下来开始insert into t1 values(1);语句，首先这里也会进入到StartTransactionCommand，不过处理如下：

// blockState的值为TBLOCK_INPROGRESS，如下：.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/
...

然后真正执行INSERT，继续

之后的函数堆栈，如下：

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command() ## here
exec_simple_query(const char * query_string) 
...

## 此时blockState的值为TBLOCK_INPROGRESS，仅作如下处理：CommandCounterIncrement();

在这里插入图片描述

至此，INFO2结束！

INFO3

接下来 savepoint sp1; 开启相关子事务，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

在这里插入图片描述

在DefineSavepoint中，因为blockState = TBLOCK_INPROGRESS，处理如下：

// src/backend/access/transam/xact.c...case TBLOCK_INPROGRESS:case TBLOCK_SUBINPROGRESS:/* Normal subtransaction start */PushTransaction();s = CurrentTransactionState;	/* changed by push */ // 上面入栈，自然 current 是指向子事务/** Savepoint names, like the TransactionState block itself, live* in TopTransactionContext.*/if (name)s->name = MemoryContextStrdup(TopTransactionContext, name);break;
...

在 PushTransaction() 中创建了一个子事务块 TransactionStateData，自然相关状态机init 和 入栈操作 如下：

	...s->parent = p;s->nestingLevel = p->nestingLevel + 1;...s->state = TRANS_DEFAULT;s->blockState = TBLOCK_SUBBEGIN;...CurrentTransactionState = s;

之后savepoint完成，继续

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command() 
exec_simple_query(const char * query_string) 
...

此时因为栈顶为子事务sp1，其 blockState = TBLOCK_SUBBEGIN，如下：

## 在CommitTransactionCommandInternal->StartSubTransaction之中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS

接下来在 ShowTransactionState(const char *str) 的打印中，因为current有parent，自然打印(递归)如下：

在这里插入图片描述

提神醒脑一：

## StartSubTransaction() 之后子事务sp1的状态机值(含变化)如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此，savepoint sp1;相关的整个执行完成，继续

接下来insert into t1 values(2);，照常如下：

StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string)
...

因此此时current是sp1，相关状态如下：

blockState：TBLOCK_SUBINPROGRESS
state     ：TRANS_INPROGRESS.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:break;
...

接下来就是真正执行INSERT，继续

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) 
...

因为blockState：TBLOCK_SUBINPROGRESS，此时的处理，如下：

			/** This is the case when we have finished executing a command* someplace within a transaction block.  We increment the command* counter and return.*  * 当我们在事务块的某个地方执行完命令时，就会出现这种情况* 我们增加命令计数器并返回*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:CommandCounterIncrement();break;

至此INFO3结束！

INFO4

接下来savepoint sp2;继续开启相关子事务，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

在这里插入图片描述

在DefineSavepoint中，因为blockState = TBLOCK_SUBINPROGRESS，处理如下：

// src/backend/access/transam/xact.c...case TBLOCK_INPROGRESS:case TBLOCK_SUBINPROGRESS:/* Normal subtransaction start */PushTransaction();s = CurrentTransactionState;	/* changed by push */ // 上面入栈，自然 current 是指向子事务/** Savepoint names, like the TransactionState block itself, live* in TopTransactionContext.*/if (name)s->name = MemoryContextStrdup(TopTransactionContext, name);break;
...

在PushTransaction()中创建了一个子事务块TransactionStateData，自然相关状态机init 和 入栈操作 如下：

	...s->parent = p;s->nestingLevel = p->nestingLevel + 1;...s->state = TRANS_DEFAULT;s->blockState = TBLOCK_SUBBEGIN;...CurrentTransactionState = s;

之后savepoint完成，继续

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command() 
exec_simple_query(const char * query_string) 
...

此时因为栈顶为子事务sp2，其blockState = TBLOCK_SUBBEGIN，如下：

## 在CommitTransactionCommandInternal->StartSubTransaction之中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS

接下来在ShowTransactionState(const char *str)的打印中，因为current有parent，自然打印(递归)如下：

在这里插入图片描述

提神醒脑二：

## StartSubTransaction() 之后子事务sp2的状态机值(含变化)如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS子事务sp1的状态机值如下：
blockState: TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此，savepoint sp2;相关的整个执行完成，继续

接下来insert into t1 values(3);，照常如下：

StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string)
...

因此此时current是sp2，相关状态如下：

blockState：TBLOCK_SUBINPROGRESS
state     ：TRANS_INPROGRESS.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:break;
...

接下来就是真正执行INSERT，继续

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) 
...

因为blockState：TBLOCK_SUBINPROGRESS，此时的处理，如下：

			/** This is the case when we have finished executing a command* someplace within a transaction block.  We increment the command* counter and return.*  * 当我们在事务块的某个地方执行完命令时，就会出现这种情况* 我们增加命令计数器并返回*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:CommandCounterIncrement();break;

至此INFO4结束！

INFO5

接下来savepoint sp3;继续开启相关子事务，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

在这里插入图片描述

在DefineSavepoint中，因为blockState = TBLOCK_SUBINPROGRESS，处理如下：

// src/backend/access/transam/xact.c...case TBLOCK_INPROGRESS:case TBLOCK_SUBINPROGRESS:/* Normal subtransaction start */PushTransaction();s = CurrentTransactionState;	/* changed by push */ // 上面入栈，自然 current 是指向子事务/** Savepoint names, like the TransactionState block itself, live* in TopTransactionContext.*/if (name)s->name = MemoryContextStrdup(TopTransactionContext, name);break;
...

在PushTransaction()中创建了一个子事务块TransactionStateData，自然相关状态机init 和 入栈操作 如下：

	...s->parent = p;s->nestingLevel = p->nestingLevel + 1;...s->state = TRANS_DEFAULT;s->blockState = TBLOCK_SUBBEGIN;...CurrentTransactionState = s;

之后savepoint完成，继续

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command() 
exec_simple_query(const char * query_string) 
...

此时因为栈顶为子事务sp3，其blockState = TBLOCK_SUBBEGIN，如下：

## 在CommitTransactionCommandInternal->StartSubTransaction之中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS

接下来在ShowTransactionState(const char *str)的打印中，因为current有parent，自然打印(递归)如下：

在这里插入图片描述

提神醒脑三：

## StartSubTransaction() 之后子事务sp3的状态机值(含变化)如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS子事务sp2的状态机值如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS子事务sp1的状态机值如下：
blockState: TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此，savepoint sp3;相关的整个执行完成，继续

接下来是 select * from t1; 和 insert into t1 values(3);，照常如下：

StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string)
...

因此此时current是sp3，相关状态如下：

blockState：TBLOCK_SUBINPROGRESS
state     ：TRANS_INPROGRESS.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:break;
...

接下来就是真正执行SELECT 和 INSERT，继续

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) 
...

因为blockState：TBLOCK_SUBINPROGRESS，此时的处理，如下：

			/** This is the case when we have finished executing a command* someplace within a transaction block.  We increment the command* counter and return.*  * 当我们在事务块的某个地方执行完命令时，就会出现这种情况* 我们增加命令计数器并返回*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:CommandCounterIncrement();break;

至此INFO5结束！

注：这里我们先后执行了SELECT和INSERT，他们在具体的处理上有一处不同，如下：

在这里插入图片描述

前者的为假；后者为真。关于这个问题，后面我将另起一篇博客详细说明这里不再赘述！

INFO6

接下来release savepoint sp2;继续相关子事务的处理(如果这个时候记不住之前事务的状态，去看提神醒脑)，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

ReleaseSavepoint(const char * name)
standard_ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc)
ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc)
PortalRunUtility(Portal portal, PlannedStmt * pstmt, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, QueryCompletion * qc) 
PortalRunMulti(Portal portal, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
PortalRun(Portal portal, long count, _Bool isTopLevel, _Bool run_once, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
exec_simple_query(const char * query_string)
...

在这里插入图片描述

如上，在ReleaseSavepoint函数中的如下循环逻辑处理：

.../** Mark "commit pending" all subtransactions up to the target* subtransaction.  The actual commits will happen when control gets to* CommitTransactionCommand.*  * 将所有子事务标记为“提交挂起”，直至目标子事务* 实际的提交将在控制到达CommitTransactionCommand时发生*/xact = CurrentTransactionState;for (;;){Assert(xact->blockState == TBLOCK_SUBINPROGRESS);xact->blockState = TBLOCK_SUBRELEASE;if (xact == target)break;xact = xact->parent;Assert(PointerIsValid(xact));}
...

// 将 sp2的子事务 sp3 的blockState的值改变： TBLOCK_SUBINPROGRESS -> TBLOCK_SUBRELEASE
// 和 sp2的blockState的值改变： TBLOCK_SUBINPROGRESS -> TBLOCK_SUBRELEASE

继续：

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string)
...

因为current是sp3，其blockState = TBLOCK_SUBRELEASE，后续处理，如下：

.../** The user issued a RELEASE command, so we end the current* subtransaction and return to the parent transaction. The parent* might be ended too, so repeat till we find an INPROGRESS* transaction or subtransaction.*  * 用户发出了RELEASE命令，因此我们结束当前子事务并返回到父事务* 父事务也可能被终止，因此重复此操作，直到找到INPROGRESS事务或子事务*/case TBLOCK_SUBRELEASE:do{CommitSubTransaction();s = CurrentTransactionState;	/* changed by pop */} while (s->blockState == TBLOCK_SUBRELEASE);Assert(s->blockState == TBLOCK_INPROGRESS ||s->blockState == TBLOCK_SUBINPROGRESS);break;
...

如上循环依次提交了栈顶TBLOCK_SUBRELEASE状态的子事务，首先是sp3 CommitSubTransaction的打印和状态修改，如下：

INFO:  CommitSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/4
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/4
INFO:  CommitSubTransaction(3) name: sp2; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 752/3/4
INFO:  CommitSubTransaction(4) name: sp3; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 753/4/4sp3的 state：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT以及 sp3 的 PopTransaction

接下来是sp2 CommitSubTransaction的打印和状态修改，如下：

INFO:  CommitSubTransaction(1) name: unnamed; blockState: INPROGRESS; state: INPROGRESS, xid/subid/cid: 739/1/4
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBINPROGRESS; state: INPROGRESS, xid/subid/cid: 740/2/4
INFO:  CommitSubTransaction(3) name: sp2; blockState: SUBRELEASE; state: INPROGRESS, xid/subid/cid: 752/3/4, children: 753sp2的 state：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT以及 sp2 的 PopTransaction

提神醒脑四：

## CommitSubTransaction() 之后子事务sp1的状态机值如下：
blockState: TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此，release savepoint sp2;相关的整个执行完成，继续

接下来select * from t1;，照常如下：

StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string)
...

因此此时current是sp1，相关状态如下：

blockState：TBLOCK_SUBINPROGRESS
state     ：TRANS_INPROGRESS.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:break;
...

接下来就是真正执行SELECT，因为上面 release 实质上commit了两个事务，所以相关insert得以保留。继续：

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) 
...

因为blockState：TBLOCK_SUBINPROGRESS，此时的处理，如下：

			/** This is the case when we have finished executing a command* someplace within a transaction block.  We increment the command* counter and return.*  * 当我们在事务块的某个地方执行完命令时，就会出现这种情况* 我们增加命令计数器并返回*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:CommandCounterIncrement();break;

至此INFO6结束！

INFO7

接下来savepoint sp1;继续开启相关子事务(创建同名savepoint)，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

在这里插入图片描述

在DefineSavepoint中，因为blockState = TBLOCK_SUBINPROGRESS，处理如下：

// src/backend/access/transam/xact.c...case TBLOCK_INPROGRESS:case TBLOCK_SUBINPROGRESS:/* Normal subtransaction start */PushTransaction();s = CurrentTransactionState;	/* changed by push */ // 上面入栈，自然 current 是指向子事务/** Savepoint names, like the TransactionState block itself, live* in TopTransactionContext.*/if (name)s->name = MemoryContextStrdup(TopTransactionContext, name);break;
...

在PushTransaction()中创建了一个子事务块TransactionStateData，自然相关状态机init 和 入栈操作 如下：

	...s->parent = p;s->nestingLevel = p->nestingLevel + 1;...s->state = TRANS_DEFAULT;s->blockState = TBLOCK_SUBBEGIN;...CurrentTransactionState = s;

之后savepoint完成，继续

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command() 
exec_simple_query(const char * query_string) 
...

此时因为栈顶为子事务第二个 sp1，其blockState = TBLOCK_SUBBEGIN，如下：

## 在CommitTransactionCommandInternal->StartSubTransaction之中，相关状态机的变化：State的值改变： TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS

接下来在ShowTransactionState(const char *str)的打印中，因为current有parent，自然打印(递归)如下：

在这里插入图片描述

提神醒脑五：

## CommitTransactionCommandInternal -> StartSubTransaction() 之后子事务sp1的状态机值(含变化)如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS子事务sp1的状态机值如下：
blockState: TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此，savepoint sp1;相关的整个执行完成，继续

接下来insert into t1 values(5);，照常如下：

StartTransactionCommand()
start_xact_command()
exec_simple_query(const char * query_string)
...

因此此时current是第二个 sp1，相关状态如下：

blockState：TBLOCK_SUBINPROGRESS
state     ：TRANS_INPROGRESS.../** We are somewhere in a transaction block or subtransaction and* about to start a new command.  For now we do nothing, but* someday we may do command-local resource initialization. (Note* that any needed CommandCounterIncrement was done by the* previous CommitTransactionCommand.)*  * 我们在某个事务块或子事务中，即将启动一个新命令* 现在我们什么都不做，但将来我们可能会进行命令本地资源初始化* (注意，任何需要的CommandCounterIncrement都是由之前的CommitTransactionCommand完成的)*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:break;
...

接下来就是真正执行INSERT，继续

CommitTransactionCommandInternal() 
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string) 
...

因为blockState：TBLOCK_SUBINPROGRESS，此时的处理，如下：

			/** This is the case when we have finished executing a command* someplace within a transaction block.  We increment the command* counter and return.*  * 当我们在事务块的某个地方执行完命令时，就会出现这种情况* 我们增加命令计数器并返回*/case TBLOCK_INPROGRESS:case TBLOCK_IMPLICIT_INPROGRESS:case TBLOCK_SUBINPROGRESS:CommandCounterIncrement();break;

至此INFO7结束！

INFO8

接下来rollback to savepoint sp1;继续相关子事务的处理(如果这个时候记不住之前事务的状态，继续去看提神醒脑)，首先也会进入如下的处理：

StartTransactionCommand() 
start_xact_command() 
exec_simple_query(const char * query_string)
...

不过由于blockState = TBLOCK_INPROGRESS，所以不做下一步处理。

继续：

RollbackToSavepoint(const char * name)
standard_ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc)
ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc) 
PortalRunUtility(Portal portal, PlannedStmt * pstmt, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, QueryCompletion * qc) 
PortalRunMulti(Portal portal, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
PortalRun(Portal portal, long count, _Bool isTopLevel, _Bool run_once, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
exec_simple_query(const char * query_string)
...

看一下相关的处理，如下：

...for (target = s; PointerIsValid(target); target = target->parent){if (PointerIsValid(target->name) && strcmp(target->name, name) == 0)break;}
.../** Mark "abort pending" all subtransactions up to the target* subtransaction.  The actual aborts will happen when control gets to* CommitTransactionCommand.*  * 将所有子事务标记为“中止挂起”，直至目标子事务* 实际的中止将在控制到达CommitTransactionCommand时发生*/xact = CurrentTransactionState;for (;;){if (xact == target)break;if (xact->blockState == TBLOCK_SUBINPROGRESS)xact->blockState = TBLOCK_SUBABORT_PENDING;else if (xact->blockState == TBLOCK_SUBABORT)xact->blockState = TBLOCK_SUBABORT_END;elseelog(FATAL, "RollbackToSavepoint: unexpected state %s",BlockStateAsString(xact->blockState));xact = xact->parent;Assert(PointerIsValid(xact));}/* And mark the target as "restart pending" */if (xact->blockState == TBLOCK_SUBINPROGRESS)xact->blockState = TBLOCK_SUBRESTART;else if (xact->blockState == TBLOCK_SUBABORT)xact->blockState = TBLOCK_SUBABORT_RESTART;
...

虽然这里有两个sp1，但是rollback to savepoint sp1;寻找是倒着进行的，自然将要被回滚的就是第二次的savepoint。这里将其blockState TBLOCK_SUBINPROGRESS -> TBLOCK_SUBRESTART。

继续：

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string)
...

当前current是第二个sp1，其blockState：TBLOCK_SUBRESTART，相关处理如下：

.../** The current subtransaction is the target of a ROLLBACK TO* command.  Abort and pop it, then start a new subtransaction* with the same name.*  * 当前子事务是ROLLBACK TO命令的目标* 中止并弹出它，然后启动具有相同名称的新子事务*/case TBLOCK_SUBRESTART:{char	   *name;int			savepointLevel;/* save name and keep Cleanup from freeing it */name = s->name;s->name = NULL;savepointLevel = s->savepointLevel;AbortSubTransaction();CleanupSubTransaction();DefineSavepoint(NULL);s = CurrentTransactionState;	/* changed by push */s->name = name;s->savepointLevel = savepointLevel;/* This is the same as TBLOCK_SUBBEGIN case */Assert(s->blockState == TBLOCK_SUBBEGIN);StartSubTransaction();s->blockState = TBLOCK_SUBINPROGRESS;}break;
...

在这里插入图片描述

这里AbortSubTransaction的打印如上所示，其中：

state：TRANS_INPROGRESS -> TRANS_ABORT

在这里插入图片描述

这里CleanupSubTransaction的打印如上所示，其中：

state：TRANS_ABORT -> TRANS_DEFAULT以及 PopTransaction

PushTransaction()
DefineSavepoint(const char * name)
CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string)
...

在DefineSavepoint之中，(栈内就剩两个事务)，current是sp1 其blockState：TBLOCK_SUBINPROGRESS，如下：

在PushTransaction()中创建了一个子事务块TransactionStateData，自然相关状态机init 和 入栈操作 如下：

	...s->parent = p; // sp1s->nestingLevel = p->nestingLevel + 1;...s->state = TRANS_DEFAULT;s->blockState = TBLOCK_SUBBEGIN;...CurrentTransactionState = s;

之后重新命令为sp1(指的是第二个sp1)，然后就可以StartSubTransaction，如下：

state：TRANS_DEFAULT -> TRANS_START -> TRANS_INPROGRESS

该过程的打印，如下：

在这里插入图片描述

在StartSubTransaction之后，新的sp1的 blockState ：TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS。

注：在整个过程中旧的sp1(第二个)被AbortSubTransaction，然后又StartSubTransaction同名的sp1。此时的提神醒脑如下：

提神醒脑六：

## CommitTransactionCommandInternal -> StartSubTransaction() 之后子事务sp1的状态机值(含变化)如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS-- 下面这个是没有的(被abotr && pop)，写在这里 只是为了方便理解
子事务sp1的状态机值如下：
blockState: TBLOCK_SUBBEGIN -> TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS子事务sp1的状态机值如下：
blockState: TBLOCK_SUBINPROGRESS
state: TRANS_INPROGRESS父事务的状态机值如下：
blockState: TBLOCK_INPROGRESS
state: TRANS_INPROGRESS

至此rollback to savepoint sp1;，结束

接下来select * from t1;，相关不再赘述。上面我们总共insert 5次，其中第5个被回滚。

注：后面我再另起文档重点介绍一下被回滚的insert 5的可见性。

至此，INFO8结束

INFO9

直接上干货，如下：

EndTransactionBlock(_Bool chain)
standard_ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc)
ProcessUtility(PlannedStmt * pstmt, const char * queryString, _Bool readOnlyTree, ProcessUtilityContext context, ParamListInfo params, QueryEnvironment * queryEnv, DestReceiver * dest, QueryCompletion * qc)
PortalRunUtility(Portal portal, PlannedStmt * pstmt, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, QueryCompletion * qc) 
PortalRunMulti(Portal portal, _Bool isTopLevel, _Bool setHoldSnapshot, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
PortalRun(Portal portal, long count, _Bool isTopLevel, _Bool run_once, DestReceiver * dest, DestReceiver * altdest, QueryCompletion * qc)
exec_simple_query(const char * query_string)
...

父sp1sp1

接下来按照反顺序，依次commit，如下：

			/** We are in a live subtransaction block.  Set up to subcommit all* open subtransactions and then commit the main transaction.*  * 我们在一个活动子事务块中* 设置为提交所有打开的子事务，然后提交主事务。*/case TBLOCK_SUBINPROGRESS:while (s->parent != NULL){if (s->blockState == TBLOCK_SUBINPROGRESS)s->blockState = TBLOCK_SUBCOMMIT;elseelog(FATAL, "EndTransactionBlock: unexpected state %s",BlockStateAsString(s->blockState));s = s->parent;}if (s->blockState == TBLOCK_INPROGRESS)s->blockState = TBLOCK_END;elseelog(FATAL, "EndTransactionBlock: unexpected state %s",BlockStateAsString(s->blockState));result = true;break;

sp1 blockState: TBLOCK_SUBINPROGRESS -> TBLOCK_SUBCOMMITsp1 blockState: TBLOCK_SUBINPROGRESS -> TBLOCK_SUBCOMMIT父 blockState: TBLOCK_INPROGRESS -> TBLOCK_END

继续：

CommitTransactionCommandInternal()
CommitTransactionCommand()
finish_xact_command()
exec_simple_query(const char * query_string)
...

当前current的blockState：TBLOCK_SUBCOMMIT，相关处理如下：

.../** The user issued a COMMIT, so we end the current subtransaction* hierarchy and perform final commit. We do this by rolling up* any subtransactions into their parent, which leads to O(N^2)* operations with respect to resource owners - this isn't that* bad until we approach a thousands of savepoints but is* necessary for correctness should after triggers create new* resource owners.*  * 用户发出了COMMIT，因此我们结束当前的子事务层次结构并执行最后的COMMIT* 我们通过将任何子事务卷到它们的父事务中来实现这一点，* 这导致了对资源所有者的O(N^2)次操作——在我们接近数千个保存点之前，这并不是那么糟糕，但是在触发器创建新的资源所有者之后，这对于正确性是必要的。*/case TBLOCK_SUBCOMMIT:do{CommitSubTransaction();s = CurrentTransactionState;	/* changed by pop */} while (s->blockState == TBLOCK_SUBCOMMIT);/* If we had a COMMIT command, finish off the main xact too */if (s->blockState == TBLOCK_END){Assert(s->parent == NULL);CommitTransaction();s->blockState = TBLOCK_DEFAULT;if (s->chain){StartTransaction();s->blockState = TBLOCK_INPROGRESS;s->chain = false;RestoreTransactionCharacteristics(&savetc);}}else if (s->blockState == TBLOCK_PREPARE){Assert(s->parent == NULL);PrepareTransaction();s->blockState = TBLOCK_DEFAULT;}elseelog(ERROR, "CommitTransactionCommand: unexpected state %s",BlockStateAsString(s->blockState));break;
...

sp1的CommitSubTransaction打印及相关状态改变，如下：

postgres=*# end;
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 752 753
INFO:  CommitSubTransaction(3) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 0/6/5state ：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT以及 PopTransaction

sp1的CommitSubTransaction打印及相关状态改变，如下：

postgres=*# end;
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 752 753
INFO:  CommitSubTransaction(3) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 0/6/5
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5 // here
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 752 753 // herestate ：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT以及 PopTransaction

父事务的CommitTransaction打印及相关状态改变，如下：

postgres=*# end;
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 752 753
INFO:  CommitSubTransaction(3) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 0/6/5
INFO:  CommitSubTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5 
INFO:  CommitSubTransaction(2) name: sp1; blockState: SUBCOMMIT; state: INPROGRESS, xid/subid/cid: 740/2/5, children: 752 753 
INFO:  CommitTransaction(1) name: unnamed; blockState: END; state: INPROGRESS, xid/subid/cid: 739/1/5, children: 740 752 753 // herestate ：TRANS_INPROGRESS -> TRANS_COMMIT -> TRANS_DEFAULT
blockState： TBLOCK_END -> TBLOCK_DEFAULT