xact.c

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/*-------------------------------------------------------------------------
 *
 * xact.c
 *	  top level transaction system support routines
 *
 * See src/backend/access/transam/README for more information.
 *
 * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.215.2.1 2005/11/22 18:23:05 momjian Exp $
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

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

#include "access/multixact.h"
#include "access/subtrans.h"
#include "access/twophase.h"
#include "access/xact.h"
#include "catalog/heap.h"
#include "catalog/index.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 "storage/fd.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/flatfiles.h"
#include "utils/guc.h"
#include "utils/inval.h"
#include "utils/memutils.h"
#include "utils/portal.h"
#include "utils/relcache.h"
#include "utils/resowner.h"
#include "pgstat.h"


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

bool		DefaultXactReadOnly = false;
bool		XactReadOnly;

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


/*
 *	transaction states - transaction state from server perspective
 */
typedef enum TransState
{
	TRANS_DEFAULT,
	TRANS_START,
	TRANS_INPROGRESS,
	TRANS_COMMIT,
	TRANS_ABORT,
	TRANS_PREPARE
} 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;	/* nest depth */
	MemoryContext curTransactionContext;		/* my xact-lifetime context */
	ResourceOwner curTransactionOwner;	/* my query resources */
	List	   *childXids;		/* subcommitted child XIDs */
	Oid			currentUser;	/* subxact start current_user */
	bool		prevXactReadOnly;		/* entry-time xact r/o state */
	struct TransactionStateData *parent;		/* back link to parent */
} TransactionStateData;

typedef TransactionStateData *TransactionState;

/*
 * childXids is currently implemented as an Oid List, relying on the
 * assumption that TransactionIds are no wider than Oid.  We use these
 * macros to provide some isolation in case that changes in the future.
 */
#define lfirst_xid(lc)				((TransactionId) lfirst_oid(lc))
#define lappend_xid(list, datum)	lappend_oid(list, (Oid) (datum))

/*
 * 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,							/* nesting level */
	NULL,						/* cur transaction context */
	NULL,						/* cur transaction resource owner */
	NIL,						/* subcommitted child Xids */
	0,							/* entry-time current userid */
	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;

/*
 * This is the value of now(), ie, the transaction start time.
 * This does not change as we enter and exit subtransactions, so we don't
 * keep it inside the TransactionState stack.
 */
static TimestampTz xactStartTimestamp;

/*
 * 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;


/*
 * 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 AssignSubTransactionId(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 void RecordTransactionAbort(void);
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 currently running a query
 *	within an executing transaction.
 */
bool
IsTransactionState(void)
{
	TransactionState s = CurrentTransactionState;

	switch (s->state)
	{
		case TRANS_DEFAULT:
			return false;
		case TRANS_START:
			return true;
		case TRANS_INPROGRESS:
			return true;
		case TRANS_COMMIT:
			return true;
		case TRANS_ABORT:
			return true;
		case TRANS_PREPARE:
			return true;
	}

	/*
	 * Shouldn't get here, but lint is not happy without this...
	 */
	return false;
}

/*
 *	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
 *
 * Get the ID of the main transaction, even if we are currently inside
 * a subtransaction.
 */
TransactionId
GetTopTransactionId(void)
{
	return TopTransactionStateData.transactionId;
}


/*
 *	GetCurrentTransactionId
 *
 * We do not assign XIDs to subtransactions until/unless this is called.
 * When we do assign an XID to a subtransaction, recursively make sure
 * its parent has one as well (this maintains the invariant that a child
 * transaction has an XID following its parent's).
 */
TransactionId
GetCurrentTransactionId(void)
{
	TransactionState s = CurrentTransactionState;

	if (!TransactionIdIsValid(s->transactionId))
		AssignSubTransactionId(s);

	return s->transactionId;
}

static void
AssignSubTransactionId(TransactionState s)
{
	ResourceOwner currentOwner;

	Assert(s->parent != NULL);
	Assert(s->state == TRANS_INPROGRESS);
	if (!TransactionIdIsValid(s->parent->transactionId))
		AssignSubTransactionId(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(true);

	SubTransSetParent(s->transactionId, s->parent->transactionId);

	/*
	 * Acquire lock on the transaction XID.  (We assume this cannot block.) We
	 * have to be sure that the lock is assigned to the transaction's
	 * 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;
}


/*
 *	GetCurrentTransactionIdIfAny
 *
 * Unlike GetCurrentTransactionId, this will return InvalidTransactionId
 * if we are currently not in a transaction, or in a transaction or
 * subtransaction that has not yet assigned itself an XID.
 */
TransactionId
GetCurrentTransactionIdIfAny(void)
{
	TransactionState s = CurrentTransactionState;

	return s->transactionId;
}


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

	return s->subTransactionId;
}


/*
 *	GetCurrentCommandId
 */
CommandId
GetCurrentCommandId(void)
{
	/* this is global to a transaction, not subtransaction-local */
	return currentCommandId;
}

/*
 *	GetCurrentTransactionStartTimestamp
 */
TimestampTz
GetCurrentTransactionStartTimestamp(void)
{
	return xactStartTimestamp;
}

/*
 *	GetCurrentTransactionNestLevel
 *
 * Note: this will return zero when not inside any transaction, one when
 * inside a top-level transaction, etc.
 */
int
GetCurrentTransactionNestLevel(void)
{
	TransactionState s = CurrentTransactionState;

	return s->nestingLevel;
}


/*
 *	TransactionIdIsCurrentTransactionId
 */
bool
TransactionIdIsCurrentTransactionId(TransactionId xid)
{
	TransactionState s;

	/*
	 * We always say that BootstrapTransactionId is "not my transaction ID"
	 * even when it is (ie, during bootstrap).	Along with the fact that
	 * transam.c always treats BootstrapTransactionId as already committed,
	 * this causes the tqual.c routines to see all tuples as committed, which
	 * is what we need during bootstrap.  (Bootstrap mode only inserts tuples,
	 * it never updates or deletes them, so all tuples can be presumed good
	 * immediately.)
	 */
	if (xid == BootstrapTransactionId)
		return false;

	/*
	 * We will return true for the Xid of the current subtransaction, any of
	 * its subcommitted children, any of its parents, or any of their
	 * previously subcommitted children.  However, a transaction being aborted
	 * is no longer "current", even though it may still have an entry on the
	 * state stack.
	 */
	for (s = CurrentTransactionState; s != NULL; s = s->parent)
	{
		ListCell   *cell;

		if (s->state == TRANS_ABORT)
			continue;
		if (!TransactionIdIsValid(s->transactionId))
			continue;			/* it can't have any child XIDs either */
		if (TransactionIdEquals(xid, s->transactionId))
			return true;
		foreach(cell, s->childXids)
		{
			if (TransactionIdEquals(xid, lfirst_xid(cell)))
				return true;
		}
	}

	return false;