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一、数据结构
静态变量
你好currenttransactionstate(当前事务处理率)
/*
*当前交易速率移动当前交易速率(当前事务处理率)
*块它将指向太平洋
* transactionatall，或henianatop-level transaction(交易量高，或henianatop-level transaction ).
*当前交易率贺盛瑞贺盛瑞。
*你好你好你好，哎哎哎toptransactionstatedata
*/
静态交易数据=& amp大型旅行车的。state=TRANS_DEFAULT。blockState=TBLOCK_DEFAULT，
}:
/*
* unreported xid holds 6 to suspublications thathvnoter
* reportedianandload _ xact _ assign记录.
*未报告的氧化物云娥xload _ xact _ assignment(移转工单)405 .吴登盛。
*/
staticintnunreportedxids
静态站dun reported xis[pgproc _ max _ cached _ sub xis]；
statutorsationstecurrencansatedata=顶级交易atedata
/*
* substancioniandcommandassignandcounter规则
*要完成交易，请播种edonotkeeptheminthestatestack。
*减法d你好commandID(命令身份证)李亚玲！李亚玲！李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲：李亚玲，吴经熊（音译),哦，天啊别动什么事。
*/
静态事务id当前事务id:
静态命令id当前命令：
静态cboolincurrentcommandidusedTransactionState
安其林安其林安其林安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳安赛琳
/*
*事务状态-事务来自服务器前景
*杨俊钦先生-吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊，吴经熊
*/
typedefensumtransstate
{
TRANS_DEFAULT
; /* idle 空闲 */
TRANS_START, /* transaction starting 事务启动 */
TRANS_INPROGRESS, /* inside a valid transaction 进行中 */
TRANS_COMMIT, /* commit in progress 提交中 */
TRANS_ABORT, /* abort in progress 回滚中 */
TRANS_PREPARE /* prepare in progress 准备中 */
} 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:subtransaction只用于非顶层事务;其他字段用于顶层事务.
*/
typedef enum TBlockState
{
/* not-in-transaction-block states 未进入事务块状态 */
TBLOCK_DEFAULT, /* idle 空闲 */
TBLOCK_STARTED, /* running single-query transaction 单个查询事务 */
/* transaction block states 事务块状态 */
TBLOCK_BEGIN, /* starting transaction block 开始事务块 */
TBLOCK_INPROGRESS, /* live transaction 进行中 */
TBLOCK_IMPLICIT_INPROGRESS, /* live transaction after implicit BEGIN 隐式事务,进行中 */
TBLOCK_PARALLEL_INPROGRESS, /* live transaction inside parallel worker 并行worker中的事务,进行中 */
TBLOCK_END, /* COMMIT received 接收到COMMIT */
TBLOCK_ABORT, /* failed xact, awaiting ROLLBACK 失败,等待ROLLBACK */
TBLOCK_ABORT_END, /* failed xact, ROLLBACK received 失败,已接收ROLLBACK */
TBLOCK_ABORT_PENDING, /* live xact, ROLLBACK received 进行中,接收到ROLLBACK */
TBLOCK_PREPARE, /* live xact, PREPARE received 进行中,接收到PREPARE */
/* subtransaction states 子事务状态 */
TBLOCK_SUBBEGIN, /* starting a subtransaction 开启 */
TBLOCK_SUBINPROGRESS, /* live subtransaction 进行中 */
TBLOCK_SUBRELEASE, /* RELEASE received 接收到RELEASE */
TBLOCK_SUBCOMMIT, /* COMMIT received while TBLOCK_SUBINPROGRESS 进行中,接收到COMMIT */
TBLOCK_SUBABORT, /* failed subxact, awaiting ROLLBACK 失败,等待ROLLBACK */
TBLOCK_SUBABORT_END, /* failed subxact, ROLLBACK received 失败,已接收ROLLBACK */
TBLOCK_SUBABORT_PENDING, /* live subxact, ROLLBACK received 进行中,接收到ROLLBACK */
TBLOCK_SUBRESTART, /* live subxact, ROLLBACK TO received 进行中,接收到ROLLBACK TO */
TBLOCK_SUBABORT_RESTART /* failed subxact, ROLLBACK TO received 失败,已接收ROLLBACK TO */
} TBlockState;
/*
* transaction state structure
* 事务状态结构体
*/
typedef struct TransactionStateData
{
//事务ID
TransactionId transactionId; /* my XID, or Invalid if none */
//子事务ID
SubTransactionId subTransactionId; /* my subxact ID */
//保存点名称
char *name; /* savepoint name, if any */
//保存点级别
int savepointLevel; /* savepoint level */
//低级别的事务状态
TransState state; /* low-level state */
//高级别的事务状态
TBlockState blockState; /* high-level state */
//事务嵌套深度
int nestingLevel; /* transaction nesting depth */
//GUC上下文嵌套深度
int gucNestLevel; /* GUC context nesting depth */
//事务生命周期上下文
MemoryContext curTransactionContext; /* my xact-lifetime context */
//查询资源
ResourceOwner curTransactionOwner; /* my query resources */
//按XID顺序保存的已提交的子事务ID
TransactionId *childXids; /* subcommitted child XIDs, in XID order */
//childXids数组大小
int nChildXids; /* # of subcommitted child XIDs */
//分配的childXids数组空间
int maxChildXids; /* allocated size of childXids[] */
//上一个CurrentUserId
Oid prevUser; /* previous CurrentUserId setting */
//上一个SecurityRestrictionContext
int prevSecContext; /* previous SecurityRestrictionContext */
//上一事务是否只读?
bool prevXactReadOnly; /* entry-time xact r/o state */
//是否处于Recovery?
bool startedInRecovery; /* did we start in recovery? */
//XID是否已保存在WAL Record中?
bool didLogXid; /* has xid been included in WAL record? */
//Enter/ExitParallelMode计数器
int parallelModeLevel; /* Enter/ExitParallelMode counter */
//父事务状态
struct TransactionStateData *parent; /* back link to parent */
} TransactionStateData;
//结构体指针
typedef TransactionStateData *TransactionState;
二、源码解读
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.
/*
* AssignTransactionId
*
* Assigns a new permanent XID to the given TransactionState.
* We do not assign XIDs to transactions until/unless this is called.
* Also, any parent TransactionStates that don't yet have XIDs are assigned
* one; this maintains the invariant that a child transaction has an XID
* following its parent's.
* 为给定的TransactionState分配一个新的持久化事务号XID.
* 在此函数调用前,我们不会为事务分配XIDs.
* 同时,所有尚未获得XIDs的父TransactionStates也会分配事务号,
* 这可以确保子事务的事务号在父事务之后.
*/
static void
AssignTransactionId(TransactionState s)
{
bool isSubXact = (s->parent != NULL);
ResourceOwner currentOwner;
bool log_unknown_top = false;
/* Assert that caller didn't screw up */
//确保调用者没有搞砸
Assert(!TransactionIdIsValid(s->transactionId));
Assert(s->state == TRANS_INPROGRESS);
/*
* Workers synchronize transaction state at the beginning of each parallel
* operation, so we can't account for new XIDs at this point.
* 在每个并行操作前,Parallel Workers同步事务状态,
* 因此我们不能在这时候请求XIDs
*/
if (IsInParallelMode() || IsParallelWorker())
elog(ERROR, "cannot assign XIDs during a parallel operation");
/*
* Ensure parent(s) have XIDs, so that a child always has an XID later
* than its parent. Mustn't recurse here, or we might get a stack overflow
* if we're at the bottom of a huge stack of subtransactions none of which
* have XIDs yet.
* 确保父事务已分配XIDs,这样可以确保子事务的XID后于父事务.
* 不能在这里递归执行,否则如果我们在一个未分配XID子事务大栈的底部,可能会遇到栈溢出
*/
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;
}
/*
* This is technically a recursive call, but the recursion will never
* be more than one layer deep.
* 递归调用,但递归不会超过一层
*/
while (parentOffset != 0)
AssignTransactionId(parents[--parentOffset]);
pfree(parents);
}
/*
* When wal_level=logical, guarantee that a subtransaction's xid can only
* be seen in the WAL stream if its toplevel xid has been logged before.
* If necessary we log an xact_assignment record with fewer than
* PGPROC_MAX_CACHED_SUBXIDS. Note that it is fine if didLogXid isn't set
* for a transaction even though it appears in a WAL record, we just might
* superfluously log something. That can happen when an xid is included
* somewhere inside a wal record, but not in XLogRecord->xl_xid, like in
* xl_standby_locks.
* 如wal_level=logical,确保子事务XID在顶层XID已被"日志"的情况只可以被WAL stream看到.
* 如果有必要，我们将使用小于PGPROC_MAX_CACHED_SUBXIDS的值来记录xact_assignment记录.
* 请注意，即使didLogXid出现在WAL记录中，如果它没有为事务设置，也没有问题，
* 我们可能只是多余地记录了一些东西。
* 当一个xid出现在WAL Record中的某个地方，但不在XLogRecord->xl_xid中
* (比如在xl_standby_locks中)时，就会发生这种情况。
*/
if (isSubXact && XLogLogicalInfoActive() &&
!TopTransactionStateData.didLogXid)
log_unknown_top = true;
/*
* Generate a new Xid and record it in PG_PROC and pg_subtrans.
* 生成一个新的XID,并记录在PG_PROC和pg_subtrans中
*
* NB: we must make the subtrans entry BEFORE the Xid appears anywhere in
* shared storage other than PG_PROC; because if there's no room for it in
* PG_PROC, the subtrans entry is needed to ensure that other backends see
* the Xid as "running". See GetNewTransactionId.
* 注意:我们必须在Xid出现在除PG_PROC之外的共享存储之前构造subtrans条目.
* 因为如果在PG_PROC没有空闲空间,子事务条目需要确保其他进程看到该XID正在运行.
* 参考函数GetNewTransactionId说明.
*
*/
s->transactionId = GetNewTransactionId(isSubXact);
if (!isSubXact)
XactTopTransactionId = s->transactionId;
if (isSubXact)
SubTransSetParent(s->transactionId, s->parent->transactionId);
/*
* If it's a top-level transaction, the predicate locking system needs to
* be told about it too.
* 如为顶层事务,谓词锁系统也需要了解此事务.
*/
if (!isSubXact)
RegisterPredicateLockingXid(s->transactionId);
/*
* Acquire lock on the transaction XID. (We assume this cannot block.) We
* have to ensure that the lock is assigned to the transaction's own
* ResourceOwner.
* 请求锁(我们假定这样做不好引起阻塞).我们必须确保锁已被分配给事务自己的ResourceOwner.
*/
currentOwner = CurrentResourceOwner;
CurrentResourceOwner = s->curTransactionOwner;
XactLockTableInsert(s->transactionId);
CurrentResourceOwner = currentOwner;
/*
* Every PGPROC_MAX_CACHED_SUBXIDS assigned transaction ids within each
* top-level transaction we issue a WAL record for the assignment. We
* include the top-level xid and all the subxids that have not yet been
* reported using XLOG_XACT_ASSIGNMENT records.
* 在每个顶级事务中分配的每个PGPROC_MAX_CACHED_SUBXIDS事务id，
* 我们都会为分配记录一条WAL记录。
* 该记录包括顶级的xid和所有尚未使用XLOG_XACT_ASSIGNMENT记录报告的子xid。
*
* This is required to limit the amount of shared memory required in a hot
* standby server to keep track of in-progress XIDs. See notes for
* RecordKnownAssignedTransactionIds().
* 在跟踪进行中的XIDs的备机上,需要控制共享内存的大小.
* 参见RecordKnownAssignedTransactionIds()函数说明.
*
* We don't keep track of the immediate parent of each subxid, only the
* top-level transaction that each subxact belongs to. This is correct in
* recovery only because aborted subtransactions are separately WAL
* logged.
* 我们不需要跟踪父事务的每个子事务,只需要跟踪子事务归属的顶层事务即可.
* 这样可行是因为在恢复中,已回滚的子事务是通过WAL单独记录的.
*
* This is correct even for the case where several levels above us didn't
* have an xid assigned as we recursed up to them beforehand.
* 即使在我们之前递归到上面的几个级别时没有分配xid的情况下，这也是正确的。
*/
if (isSubXact && XLogStandbyInfoActive())
{
unreportedXids[nUnreportedXids] = s->transactionId;
nUnreportedXids++;
/*
* ensure this test matches similar one in
* RecoverPreparedTransactions()
* 确保在RecoverPreparedTransactions()中可以匹配到相似的.
*/
if (nUnreportedXids >= PGPROC_MAX_CACHED_SUBXIDS ||
log_unknown_top)
{
xl_xact_assignment xlrec;
/*
* xtop is always set by now because we recurse up transaction
* stack to the highest unassigned xid and then come back down
* xtop现在已经设置好了，因为我们将事务堆栈递归到最高的未分配的xid，然后再返回
*/
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;
/* mark top, not current xact as having been logged */
//标记为最顶层,而不是当前已记录日志的xact
TopTransactionStateData.didLogXid = true;
}
}
}
三、跟踪分析
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网站，小编将为大家输出更多高质量的实用文章！
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