m4_comment([$Id: txn_begin.so,v 10.80 2006/12/13 18:09:09 bostic Exp $])

define(M4PAGELOCAL,
    [txn_begin, DB_READ_COMMITTED, DB_READ_UNCOMMITTED, DB_TXN_NOSYNC,
    DB_TXN_NOWAIT, DB_TXN_NOWAIT, DB_TXN_SNAPSHOT, DB_TXN_SYNC, DB_TXN_WAIT,
    DB_TXN_WRITE_NOSYNC])
include(m4/m4.seealso)

m4_pf_header(m4_ref(txn_begin),
ifelse(M4API, C_API, [dnl
int
DB_ENV-__GT__txn_begin(DB_ENV *env,
    DB_TXN *parent, DB_TXN **tid, u_int32_t flags);
])
ifelse(M4API, CXX_API, [dnl
int
DbEnv::txn_begin(DbTxn *parent, DbTxn **tid, u_int32_t flags);
]))

m4_p([dnl
The m4_ref(txn_begin) method creates a new transaction in the environment
and copies a pointer to a m4_ref(DbTxn) that uniquely identifies it into
the memory to which m4_arg(tid) refers.  Calling the m4_ref(txn_abort),
m4_ref(txn_commit) or m4_refT(txn_discard)s will discard the returned
handle.])

m4_p([m4_bold([dnl
Note: Transactions may only span threads if they do so serially;
that is, each transaction must be active in only a single thread
of control at a time.  This restriction holds for parents of nested
transactions as well; no two children may be concurrently active in
more than one thread of control at any one time.])])

m4_p([m4_bold([dnl
Note: Cursors may not span transactions; that is, each cursor must be
opened and closed within a single transaction.])])

m4_p([m4_bold([dnl
Note: A parent transaction may not issue any m4_db operations -- except for
m4_ref(txn_begin), m4_ref(txn_abort) and m4_ref(txn_commit) -- while it has
active child transactions (child transactions that have not yet been
committed or aborted).])])

m4_return(txn_begin, std)

m4_parambegin
m4_param(flags, [dnl
m4_sf_or_may

m4_tagbegin
m4_tag(m4_idef(DB_READ_COMMITTED), [dnl
This transaction will have degree 2 isolation.  This provides for cursor
stability but not repeatable reads.  Data items which have been
previously read by this transaction may be deleted or modified by other
transactions before this transaction completes.])

m4_tag(m4_idef(DB_READ_UNCOMMITTED), [dnl
This transaction will have degree 1 isolation.  Read operations
performed by the transaction may read modified but not yet committed
data.  Silently ignored if the m4_ref(DB_READ_UNCOMMITTED) flag was not
specified when the underlying database was opened.])

m4_tag(m4_idef(DB_TXN_NOSYNC), [dnl
Do not synchronously flush the log when this transaction commits or
prepares. This means the transaction will exhibit the ACI (atomicity,
consistency, and isolation) properties, but not D (durability); that is,
database integrity will be maintained but it is possible that this
transaction may be undone during recovery.
m4_p([dnl
This behavior may be set for a m4_db environment using the
m4_refT(dbenv_set_flags).  Any value specified to this method overrides
that setting.])])

m4_tag(m4_idef(DB_TXN_NOWAIT), [dnl
If a lock is unavailable for any m4_db operation performed in the context
of this transaction, cause the operation to
ifelse(M4EXCEPT, return_only, [dnl
return m4_ref(DB_LOCK_DEADLOCK) (or m4_ref(DB_LOCK_NOTGRANTED) if the
database environment has been configured using the
m4_ref(DB_TIME_NOTGRANTED) flag).],[dnl
either return m4_ref(DB_LOCK_DEADLOCK) or throw a
m4_ref(DbDeadlockException) exception (or return
m4_ref(DB_LOCK_NOTGRANTED) or throw a m4_ref(DbLockNotGrantedException)
exception if the database environment has been configured using the
m4_ref(DB_TIME_NOTGRANTED) flag).])
m4_p([dnl
This behavior may be set for a m4_db environment using the
m4_refT(dbenv_set_flags).  Any value specified to this method overrides
that setting.])])

m4_tag(m4_idef(DB_TXN_SNAPSHOT), [dnl
This transaction will execute with m4_link(M4RELDIR/ref/transapp/read,
snapshot isolation).  For databases with the m4_ref(DB_MULTIVERSION)
flag set, data values will be read as they are when the transaction
begins, without taking read locks.  Silently ignored for operations on
databases with m4_ref(DB_MULTIVERSION) not set on the underlying
database (read locks are acquired).
m4_p([dnl
The error m4_idef(DB_LOCK_DEADLOCK) will be returned from update
operations if a snapshot transaction attempts to update data
which was modified after the snapshot transaction read it.])])

m4_tag(m4_idef(DB_TXN_SYNC), [dnl
Synchronously flush the log when this transaction commits or prepares.
This means the transaction will exhibit all of the ACID (atomicity,
consistency, isolation, and durability) properties.
m4_p([dnl
This behavior is the default for m4_db environments unless the
m4_ref(DB_TXN_NOSYNC) flag was specified to the
m4_refT(dbenv_set_flags).  Any value specified to this method overrides
that setting.])])

m4_tag(m4_idef(DB_TXN_WAIT), [dnl
If a lock is unavailable for any m4_db operation performed in the context
of this transaction, wait for the lock.
m4_p([dnl
This behavior is the default for m4_db environments unless the
m4_ref(DB_TXN_NOWAIT) flag was specified to the
m4_refT(dbenv_set_flags).  Any value specified to this method overrides
that setting.])])

m4_tag(m4_idef(DB_TXN_WRITE_NOSYNC), [dnl
Write, but do not synchronously flush, the log when this transaction
commits.  This means the transaction will exhibit the ACI (atomicity,
consistency, and isolation) properties, but not D (durability); that is,
database integrity will be maintained, but if the system fails, it is
possible some number of the most recently committed transactions may be
undone during recovery.  The number of transactions at risk is governed
by how often the system flushes dirty buffers to disk and how often the
log is flushed or checkpointed.
m4_p([dnl
This behavior may be set for a m4_db environment using the
m4_refT(dbenv_set_flags).  Any value specified to this method overrides
that setting.])])
m4_tagend])

m4_param(parent, [dnl
If the m4_arg(parent) parameter is non-NULL, the new transaction will
be a nested transaction, with the transaction indicated by
m4_arg(parent) as its parent.  Transactions may be nested to any level.
In the presence of distributed transactions and two-phase commit, only
the parental transaction, that is a transaction without a m4_arg(parent)
specified, should be passed as an parameter to m4_ref(txn_prepare).])
m4_paramend

m4_err(txn_begin, memory,
[maximum number of concurrent transactions has been reached])

m4_seealso(DbTxn)
m4_page_footer