本篇内容介绍了“postgresql中函数AssignTransactionId的实现逻辑是什么”的有关知识,在实际案例的操作过程中,不少人都会遇到这样的困境,接下来就让小编带领大家学习一下如何处理这些情况
本篇内容介绍了“postgresql中函数AssignTransactionId的实现逻辑是什么”的有关知识,在实际案例的操作过程中,不少人都会遇到这样的困境,接下来就让小编带领大家学习一下如何处理这些情况吧!希望大家仔细阅读,能够学有所成!
静态变量
当前事务状态CurrentTransactionState
static TransactionStateData TopTransactionStateData = {
.state = TRANS_DEFAULT,
.blockState = TBLOCK_DEFAULT,
};
static int nUnreportedXids;
static TransactionId unreportedXids[PGPROC_MAX_CACHED_SUBXIDS];
static TransactionState CurrentTransactionState = &TopTransactionStateData;
static SubTransactionId currentSubTransactionId;
static CommandId currentCommandId;
static bool currentCommandIdUsed;
TransactionState
事务状态结构体
typedef enum TransState
{
TRANS_DEFAULT,
TRANS_START,
TRANS_INPROGRESS,
TRANS_COMMIT,
TRANS_ABORT,
TRANS_PREPARE
} TransState;
typedef enum TBlockState
{
TBLOCK_DEFAULT,
TBLOCK_STARTED,
TBLOCK_BEGIN,
TBLOCK_INPROGRESS,
TBLOCK_IMPLICIT_INPROGRESS,
TBLOCK_PARALLEL_INPROGRESS,
TBLOCK_END,
TBLOCK_ABORT,
TBLOCK_ABORT_END,
TBLOCK_ABORT_PENDING,
TBLOCK_PREPARE,
TBLOCK_SUBBEGIN,
TBLOCK_SUBINPROGRESS,
TBLOCK_SUBRELEASE,
TBLOCK_SUBCOMMIT,
TBLOCK_SUBABORT,
TBLOCK_SUBABORT_END,
TBLOCK_SUBABORT_PENDING,
TBLOCK_SUBRESTART,
TBLOCK_SUBABORT_RESTART
} TBlockState;
typedef struct TransactionStateData
{
//事务ID
TransactionId transactionId;
//子事务ID
SubTransactionId subTransactionId;
//保存点名称
char *name;
//保存点级别
int savepointLevel;
//低级别的事务状态
TransState state;
//高级别的事务状态
TBlockState blockState;
//事务嵌套深度
int nestingLevel;
//GUC上下文嵌套深度
int gucNestLevel;
//事务生命周期上下文
MemoryContext curTransactionContext;
//查询资源
ResourceOwner curTransactionOwner;
//按XID顺序保存的已提交的子事务ID
TransactionId *childXids;
//childXids数组大小
int nChildXids;
//分配的childXids数组空间
int maxChildXids;
//上一个CurrentUserId
Oid prevUser;
//上一个SecurityRestrictionContext
int prevSecContext;
//上一事务是否只读?
bool prevXactReadOnly;
//是否处于Recovery?
bool startedInRecovery;
//XID是否已保存在WAL Record中?
bool didLogXid;
//Enter/ExitParallelMode计数器
int parallelModeLevel;
//父事务状态
struct TransactionStateData *parent;
} TransactionStateData;
//结构体指针
typedef TransactionStateData *TransactionState;
AssignTransactionId函数,给定的TransactionState分配一个新的持久化事务号XID,在此函数调用前,不会为事务分配XIDs.
static void
AssignTransactionId(TransactionState s)
{
bool isSubXact = (s->parent != NULL);
ResourceOwner currentOwner;
bool log_unknown_top = false;
//确保调用者没有搞砸
Assert(!TransactionIdIsValid(s->transactionId));
Assert(s->state == TRANS_INPROGRESS);
if (IsInParallelMode() || IsParallelWorker())
elog(ERROR, "cannot assign XIDs during a parallel operation");
if (isSubXact && !TransactionIdIsValid(s->parent->transactionId))
{
TransactionState p = s->parent;
TransactionState *parents;
size_t parentOffset = 0;
parents = palloc(sizeof(TransactionState) * s->nestingLevel);
while (p != NULL && !TransactionIdIsValid(p->transactionId))
{
parents[parentOffset++] = p;
p = p->parent;
}
while (parentOffset != 0)
AssignTransactionId(parents[--parentOffset]);
pfree(parents);
}
if (isSubXact && XLogLogicalInfoActive() &&
!TopTransactionStateData.didLogXid)
log_unknown_top = true;
s->transactionId = GetNewTransactionId(isSubXact);
if (!isSubXact)
XactTopTransactionId = s->transactionId;
if (isSubXact)
SubTransSetParent(s->transactionId, s->parent->transactionId);
if (!isSubXact)
ReGISterPredicateLockingXid(s->transactionId);
currentOwner = CurrentResourceOwner;
CurrentResourceOwner = s->curTransactionOwner;
XactLockTableInsert(s->transactionId);
CurrentResourceOwner = currentOwner;
if (isSubXact && XLogStandbyInfoActive())
{
unreportedXids[nUnreportedXids] = s->transactionId;
nUnreportedXids++;
if (nUnreportedXids >= PGPROC_MAX_CACHED_SUBXIDS ||
log_unknown_top)
{
xl_xact_assignment xlrec;
xlrec.xtop = GetTopTransactionId();
Assert(TransactionIdIsValid(xlrec.xtop));
xlrec.nsubxacts = nUnreportedXids;
XLogBeginInsert();
XLogRegisterData((char *) &xlrec, MinSizeOfXactAssignment);
XLogRegisterData((char *) unreportedXids,
nUnreportedXids * sizeof(TransactionId));
(void) XLogInsert(RM_XACT_ID, XLOG_XACT_ASSIGNMENT);
nUnreportedXids = 0;
//标记为最顶层,而不是当前已记录日志的xact
TopTransactionStateData.didLogXid = true;
}
}
}
执行txid_current,触发函数调用
11:10:36 (xdb@[local]:5432)testdb=# begin;
BEGIN
11:40:20 (xdb@[local]:5432)testdb=#* select txid_current_if_assigned();
txid_current_if_assigned
--------------------------
(1 row)
11:40:43 (xdb@[local]:5432)testdb=#* select txid_current();
启动gdb,设置断点
(gdb) b AssignTransactionId
Breakpoint 5 at 0x546a4c: file xact.c, line 491.
(gdb) c
Continuing.
Breakpoint 5, AssignTransactionId (s=0xf9c720 <TopTransactionStateData>) at xact.c:491
491 bool isSubXact = (s->parent != NULL);
(gdb)
查看调用栈
(gdb) bt
#0 AssignTransactionId (s=0xf9c720 <TopTransactionStateData>) at xact.c:491
#1 0x000000000054693D in GetTopTransactionId () at xact.c:392
#2 0x00000000009fe1f3 in txid_current (fcinfo=0x25835a0) at txid.c:443
#3 0x00000000006cfebd in ExecInterpExpr (state=0x25834b8, econtext=0x25831a8, isnull=0x7ffe3d4a31f7)
at execExprInterp.c:654
#4 0x00000000006d1ac6 in ExecInterpExprStillValid (state=0x25834b8, econtext=0x25831a8, isNull=0x7ffe3d4a31f7)
at execExprInterp.c:1786
#5 0x00000000007140dd in ExecEvalExprSwitchContext (state=0x25834b8, econtext=0x25831a8, isNull=0x7ffe3d4a31f7)
at ../../../src/include/executor/executor.h:303
#6 0x000000000071414b in ExecProject (projInfo=0x25834b0) at ../../../src/include/executor/executor.h:337
#7 0x0000000000714323 in ExecResult (pstate=0x2583090) at nodeResult.c:136
#8 0x00000000006e4c30 in ExecProcNodeFirst (node=0x2583090) at execProcnode.c:445
#9 0x00000000006d9974 in ExecProcNode (node=0x2583090) at ../../../src/include/executor/executor.h:237
#10 0x00000000006dc22d in ExecutePlan (estate=0x2582e78, planstate=0x2583090, use_parallel_mode=false,
operation=CMD_SELECT, sendTuples=true, numberTuples=0, direction=ForwardScanDirection, dest=0x24cd0a0,
execute_once=true) at execMain.c:1723
#11 0x00000000006d9f5c in standard_ExecutorRun (queryDesc=0x256b0c8, direction=ForwardScanDirection, count=0,
execute_once=true) at execMain.c:364
#12 0x00000000006d9d7f in ExecutorRun (queryDesc=0x256b0c8, direction=ForwardScanDirection, count=0, execute_once=true)
at execMain.c:307
#13 0x00000000008ccf5a in PortalRunSelect (portal=0x250c748, forward=true, count=0, dest=0x24cd0a0) at pquery.c:932
#14 0x00000000008ccbf3 in PortalRun (portal=0x250c748, count=9223372036854775807, isTopLevel=true, run_once=true,
dest=0x24cd0a0, altdest=0x24cd0a0, completionTag=0x7ffe3d4a3570 "") at pquery.c:773
#15 0x00000000008c6b1e in exec_simple_query (query_string=0x24a6ec8 "select txid_current();") at postgres.c:1145
#16 0x00000000008cae70 in PostgresMain (arGC=1, argv=0x24d2dc8, dbname=0x24d2c30 "testdb", username=0x24a3ba8 "xdb")
at postgres.c:4182
#17 0x000000000082642b in BackendRun (port=0x24c8c00) at postmaster.c:4361
---Type <return> to continue, or q <return> to quit---
#18 0x0000000000825b8f in BackendStartup (port=0x24c8c00) at postmaster.c:4033
#19 0x0000000000821f1c in ServerLoop () at postmaster.c:1706
#20 0x00000000008217b4 in PostmasterMain (argc=1, argv=0x24a1b60) at postmaster.c:1379
#21 0x00000000007488ef in main (argc=1, argv=0x24a1b60) at main.c:228
输入参数TransactionState(全局变量,指向TopTransactionStateData)
(gdb) p s
$13 = (TransactionState) 0xf9c720 <TopTransactionStateData>
(gdb) p *s
$14 = {transactionId = 0, subTransactionId = 1, name = 0x0, savepointLevel = 0, state = TRANS_INPROGRESS,
blockState = TBLOCK_INPROGRESS, nestingLevel = 1, gucNestLevel = 1, curTransactionContext = 0x2523850,
curTransactionOwner = 0x24d4868, childXids = 0x0, nChildXids = 0, maxChildXids = 0, prevUser = 10, prevSecContext = 0,
prevXactReadOnly = false, startedInRecovery = false, didLogXid = false, parallelModeLevel = 0, parent = 0x0}
(gdb)
初始化部分变量并验证
(gdb) n
493 bool log_unknown_top = false;
(gdb)
496 Assert(!TransactionIdIsValid(s->transactionId));
(gdb)
497 Assert(s->state == TRANS_INPROGRESS);
(gdb)
获取事务号
(gdb)
503 if (IsInParallelMode() || IsParallelWorker())
(gdb)
512 if (isSubXact && !TransactionIdIsValid(s->parent->transactionId))
(gdb)
545 if (isSubXact && XLogLogicalInfoActive() &&
(gdb)
557 s->transactionId = GetNewTransactionId(isSubXact);
(gdb)
558 if (!isSubXact)
(gdb) p s->transactionId
$15 = 2407
(gdb)
注册,并设置其他信息
(gdb) n
559 XactTopTransactionId = s->transactionId;
(gdb)
561 if (isSubXact)
(gdb)
568 if (!isSubXact)
(gdb)
569 RegisterPredicateLockingXid(s->transactionId);
(gdb)
576 currentOwner = CurrentResourceOwner;
(gdb)
577 CurrentResourceOwner = s->curTransactionOwner;
(gdb)
579 XactLockTableInsert(s->transactionId);
(gdb)
581 CurrentResourceOwner = currentOwner;
(gdb)
601 if (isSubXact && XLogStandbyInfoActive())
(gdb)
635 }
完成调用
(gdb)
GetTopTransactionId () at xact.c:393
393 return XactTopTransactionId;
(gdb)
“Postgresql中函数AssignTransactionId的实现逻辑是什么”的内容就介绍到这里了,感谢大家的阅读。如果想了解更多行业相关的知识可以关注编程网网站,小编将为大家输出更多高质量的实用文章!
--结束END--
本文标题: PostgreSQL中函数AssignTransactionId的实现逻辑是什么
本文链接: https://lsjlt.com/news/64274.html(转载时请注明来源链接)
有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341
2024-10-23
2024-10-22
2024-10-22
2024-10-22
2024-10-22
2024-10-22
2024-10-22
2024-10-22
2024-10-22
2024-10-22
回答
回答
回答
回答
回答
回答
回答
回答
回答
回答
0