xact.c

postgresql8.3.4源码,开源数据库

/*-------------------------------------------------------------------------
 *
 * xact.c
 *	  top level transaction system support routines
 *
 * See src/backend/access/transam/README for more information.
 *
 * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.257.2.2 2008/04/26 23:35:33 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <time.h>
#include <unistd.h>

#include "access/multixact.h"
#include "access/subtrans.h"
#include "access/transam.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/namespace.h"
#include "commands/async.h"
#include "commands/tablecmds.h"
#include "commands/trigger.h"
#include "executor/spi.h"
#include "libpq/be-fsstubs.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/lmgr.h"
#include "storage/procarray.h"
#include "storage/sinvaladt.h"
#include "storage/smgr.h"
#include "utils/combocid.h"
#include "utils/flatfiles.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/relcache.h"
#include "utils/xml.h"


/*
 *	User-tweakable parameters
 */
int			DefaultXactIsoLevel = XACT_READ_COMMITTED;
int			XactIsoLevel;

bool		DefaultXactReadOnly = false;
bool		XactReadOnly;

bool		XactSyncCommit = true;

int			CommitDelay = 0;	/* precommit delay in microseconds */
int			CommitSiblings = 5; /* # concurrent xacts needed to sleep */

/*
 * MyXactAccessedTempRel is set when a temporary relation is accessed.
 * We don't allow PREPARE TRANSACTION in that case.  (This is global
 * so that it can be set from heapam.c.)
 */
bool		MyXactAccessedTempRel = false;


/*
 *	transaction states - transaction state from server perspective
 */
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
 *
 * Note: the subtransaction states are used only for non-topmost
 * transactions; the others appear only in the topmost transaction.
 */
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_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_SUBEND,				/* RELEASE received */
	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;

/*
 *	transaction state structure
 */
typedef struct TransactionStateData
{
	TransactionId transactionId;	/* my XID, or Invalid if none */
	SubTransactionId subTransactionId;	/* my subxact ID */
	char	   *name;			/* savepoint name, if any */
	int			savepointLevel; /* savepoint level */
	TransState	state;			/* low-level state */
	TBlockState blockState;		/* high-level state */
	int			nestingLevel;	/* transaction nesting depth */
	int			gucNestLevel;	/* GUC context nesting depth */
	MemoryContext curTransactionContext;		/* my xact-lifetime context */
	ResourceOwner curTransactionOwner;	/* my query resources */
	TransactionId *childXids;	/* subcommitted child XIDs, in XID order */
	int			nChildXids;		/* # of subcommitted child XIDs */
	int			maxChildXids;	/* allocated size of childXids[] */
	Oid			prevUser;		/* previous CurrentUserId setting */
	bool		prevSecDefCxt;	/* previous SecurityDefinerContext setting */
	bool		prevXactReadOnly;		/* entry-time xact r/o state */
	struct TransactionStateData *parent;		/* back link to parent */
} TransactionStateData;

typedef TransactionStateData *TransactionState;

/*
 * CurrentTransactionState always points to the current transaction state
 * block.  It will point to TopTransactionStateData when not in a
 * transaction at all, or when in a top-level transaction.
 */
static TransactionStateData TopTransactionStateData = {
	0,							/* transaction id */
	0,							/* subtransaction id */
	NULL,						/* savepoint name */
	0,							/* savepoint level */
	TRANS_DEFAULT,				/* transaction state */
	TBLOCK_DEFAULT,				/* transaction block state from the client
								 * perspective */
	0,							/* transaction nesting depth */
	0,							/* GUC context nesting depth */
	NULL,						/* cur transaction context */
	NULL,						/* cur transaction resource owner */
	NULL,						/* subcommitted child Xids */
	0,							/* # of subcommitted child Xids */
	0,							/* allocated size of childXids[] */
	InvalidOid,					/* previous CurrentUserId setting */
	false,						/* previous SecurityDefinerContext setting */
	false,						/* entry-time xact r/o state */
	NULL						/* link to parent state block */
};

static TransactionState CurrentTransactionState = &TopTransactionStateData;

/*
 * The subtransaction ID and command ID assignment counters are global
 * to a whole transaction, so we do not keep them in the state stack.
 */
static SubTransactionId currentSubTransactionId;
static CommandId currentCommandId;
static bool currentCommandIdUsed;

/*
 * xactStartTimestamp is the value of transaction_timestamp().
 * stmtStartTimestamp is the value of statement_timestamp().
 * xactStopTimestamp is the time at which we log a commit or abort WAL record.
 * These do not change as we enter and exit subtransactions, so we don't
 * keep them inside the TransactionState stack.
 */
static TimestampTz xactStartTimestamp;
static TimestampTz stmtStartTimestamp;
static TimestampTz xactStopTimestamp;

/*
 * GID to be used for preparing the current transaction.  This is also
 * global to a whole transaction, so we don't keep it in the state stack.
 */
static char *prepareGID;

/*
 * Some commands want to force synchronous commit.
 */
static bool forceSyncCommit = false;

/*
 * Private context for transaction-abort work --- we reserve space for this
 * at startup to ensure that AbortTransaction and AbortSubTransaction can work
 * when we've run out of memory.
 */
static MemoryContext TransactionAbortContext = NULL;

/*
 * List of add-on start- and end-of-xact callbacks
 */
typedef struct XactCallbackItem
{
	struct XactCallbackItem *next;
	XactCallback callback;
	void	   *arg;
} XactCallbackItem;

static XactCallbackItem *Xact_callbacks = NULL;

/*
 * List of add-on start- and end-of-subxact callbacks
 */
typedef struct SubXactCallbackItem
{
	struct SubXactCallbackItem *next;
	SubXactCallback callback;
	void	   *arg;
} SubXactCallbackItem;

static SubXactCallbackItem *SubXact_callbacks = NULL;


/* local function prototypes */
static void AssignTransactionId(TransactionState s);
static void AbortTransaction(void);
static void AtAbort_Memory(void);
static void AtCleanup_Memory(void);
static void AtAbort_ResourceOwner(void);
static void AtCommit_LocalCache(void);
static void AtCommit_Memory(void);
static void AtStart_Cache(void);
static void AtStart_Memory(void);
static void AtStart_ResourceOwner(void);
static void CallXactCallbacks(XactEvent event);
static void CallSubXactCallbacks(SubXactEvent event,
					 SubTransactionId mySubid,
					 SubTransactionId parentSubid);
static void CleanupTransaction(void);
static void CommitTransaction(void);
static TransactionId RecordTransactionAbort(bool isSubXact);
static void StartTransaction(void);

static void RecordSubTransactionCommit(void);
static void StartSubTransaction(void);
static void CommitSubTransaction(void);
static void AbortSubTransaction(void);
static void CleanupSubTransaction(void);
static void PushTransaction(void);
static void PopTransaction(void);

static void AtSubAbort_Memory(void);
static void AtSubCleanup_Memory(void);
static void AtSubAbort_ResourceOwner(void);
static void AtSubCommit_Memory(void);
static void AtSubStart_Memory(void);
static void AtSubStart_ResourceOwner(void);

static void ShowTransactionState(const char *str);
static void ShowTransactionStateRec(TransactionState state);
static const char *BlockStateAsString(TBlockState blockState);
static const char *TransStateAsString(TransState state);


/* ----------------------------------------------------------------
 *	transaction state accessors
 * ----------------------------------------------------------------
 */

/*
 *	IsTransactionState
 *
 *	This returns true if we are inside a valid transaction; that is,
 *	it is safe to initiate database access, take heavyweight locks, etc.
 */
bool
IsTransactionState(void)
{
	TransactionState s = CurrentTransactionState;

	/*
	 * TRANS_DEFAULT and TRANS_ABORT are obviously unsafe states.  However, we
	 * also reject the startup/shutdown states TRANS_START, TRANS_COMMIT,
	 * TRANS_PREPARE since it might be too soon or too late within those
	 * transition states to do anything interesting.  Hence, the only "valid"
	 * state is TRANS_INPROGRESS.
	 */
	return (s->state == TRANS_INPROGRESS);
}

/*
 *	IsAbortedTransactionBlockState
 *
 *	This returns true if we are currently running a query
 *	within an aborted transaction block.
 */
bool
IsAbortedTransactionBlockState(void)
{
	TransactionState s = CurrentTransactionState;

	if (s->blockState == TBLOCK_ABORT ||
		s->blockState == TBLOCK_SUBABORT)
		return true;

	return false;
}


/*
 *	GetTopTransactionId
 *
 * This will return the XID of the main transaction, assigning one if
 * it's not yet set.  Be careful to call this only inside a valid xact.
 */
TransactionId
GetTopTransactionId(void)
{
	if (!TransactionIdIsValid(TopTransactionStateData.transactionId))
		AssignTransactionId(&TopTransactionStateData);
	return TopTransactionStateData.transactionId;
}

/*
 *	GetTopTransactionIdIfAny
 *
 * This will return the XID of the main transaction, if one is assigned.
 * It will return InvalidTransactionId if we are not currently inside a
 * transaction, or inside a transaction that hasn't yet been assigned an XID.
 */
TransactionId
GetTopTransactionIdIfAny(void)
{
	return TopTransactionStateData.transactionId;
}

/*
 *	GetCurrentTransactionId
 *
 * This will return the XID of the current transaction (main or sub
 * transaction), assigning one if it's not yet set.  Be careful to call this
 * only inside a valid xact.
 */
TransactionId
GetCurrentTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	if (!TransactionIdIsValid(s->transactionId))
		AssignTransactionId(s);
	return s->transactionId;
}

/*
 *	GetCurrentTransactionIdIfAny
 *
 * This will return the XID of the current sub xact, if one is assigned.
 * It will return InvalidTransactionId if we are not currently inside a
 * transaction, or inside a transaction that hasn't been assigned an XID yet.
 */
TransactionId
GetCurrentTransactionIdIfAny(void)
{
	return CurrentTransactionState->transactionId;
}


/*
 * 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.
 */
static void
AssignTransactionId(TransactionState s)
{
	bool		isSubXact = (s->parent != NULL);
	ResourceOwner currentOwner;

	/* Assert that caller didn't screw up */
	Assert(!TransactionIdIsValid(s->transactionId));
	Assert(s->state == TRANS_INPROGRESS);

	/*
	 * Ensure parent(s) have XIDs, so that a child always has an XID later
	 * than its parent.
	 */
	if (isSubXact && !TransactionIdIsValid(s->parent->transactionId))
		AssignTransactionId(s->parent);

	/*
	 * Generate a new Xid and record it in PG_PROC and pg_subtrans.
	 *
	 * 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.
	 */
	s->transactionId = GetNewTransactionId(isSubXact);

	if (isSubXact)
		SubTransSetParent(s->transactionId, s->parent->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.
	 */
	currentOwner = CurrentResourceOwner;
	PG_TRY();
	{
		CurrentResourceOwner = s->curTransactionOwner;
		XactLockTableInsert(s->transactionId);
	}
	PG_CATCH();
	{
		/* Ensure CurrentResourceOwner is restored on error */
		CurrentResourceOwner = currentOwner;
		PG_RE_THROW();
	}
	PG_END_TRY();
	CurrentResourceOwner = currentOwner;
}


/*
 *	GetCurrentSubTransactionId
 */
SubTransactionId
GetCurrentSubTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	return s->subTransactionId;
}


/*
 *	GetCurrentCommandId
 *
 * "used" must be TRUE if the caller intends to use the command ID to mark
 * inserted/updated/deleted tuples.  FALSE means the ID is being fetched
 * for read-only purposes (ie, as a snapshot validity cutoff).  See
 * CommandCounterIncrement() for discussion.
 */
CommandId
GetCurrentCommandId(bool used)
{
	/* this is global to a transaction, not subtransaction-local */
	if (used)
		currentCommandIdUsed = true;
	return currentCommandId;
}

/*
 *	GetCurrentTransactionStartTimestamp
 */