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Add support for DEFERRED, IMMEDIATE, and EXCLUSIVE transactions. (CVS 2000)

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FossilOrigin-Name: 81ff8107ad63113782cf5a9ba7a512496114ba08
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drh
2004-10-05 02:41:42 +00:00
parent 9a43267ba2
commit 684917c269
18 changed files with 249 additions and 119 deletions
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www/lang.tcl
+38 -2
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@@ -1,7 +1,7 @@
#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.72 2004/09/08 13:06:21 drh Exp $}
set rcsid {$Id: lang.tcl,v 1.73 2004/10/05 02:41:43 drh Exp $}
source common.tcl
header {Query Language Understood by SQLite}
puts {
@@ -169,7 +169,7 @@ the main database were ":memory:".
Section {BEGIN TRANSACTION} transaction
Syntax {sql-statement} {
BEGIN [TRANSACTION [<name>]]
BEGIN [ DEFERRED | IMMEDIATE | EXCLUSIVE ] [TRANSACTION [<name>]]
}
Syntax {sql-statement} {
END [TRANSACTION [<name>]]
@@ -207,6 +207,42 @@ clause for additional information about the ROLLBACK
conflict resolution algorithm.
</p>
<p>
In SQLite version 3.0.8 and later, transactions can be deferred,
immediate, or exclusive. Deferred means that no locks are acquired
on the database until the database is first accessed. Thus with a
deferred transaction, the BEGIN statement itself does nothing. Locks
are not acquired until the first read or write operation. The first read
operation against a database creates a SHARED lock and the first
write operation creates a RESERVED lock. Because the acquisition of
locks is deferred until they are needed, it is possible that another
thread or process could create a separate transaction and write to
the database after the BEGIN on the current thread has executed.
If the transation is immediate, then RESERVED locks
are acquired on all databases as soon as the BEGIN command is
executed, without waiting for the
database to be used. After a BEGIN IMMEDIATE, you are guaranteed that
no other thread or process will be able to write to the database or
do a BEGIN IMMEDIATE or BEGIN EXCLUSIVE. Other processes can continue
to read from the database, however. An exclusive transaction causes
EXCLUSIVE locks to be acquired on all databases. After a BEGIN
EXCLUSIVE, you are guaranteed that no other thread or process will
be able to read or write the database until the transaction is
complete.
</p>
<p>
A description of the meaning of SHARED, RESERVED, and EXCLUSIVE locks
is available <a href="lockingv3.html">separately</a>.
</p>
<p>
The default behavior for SQLite version 3.0.8 is a
deferred transaction. For SQLite version 3.0.0 through 3.0.7,
deferred is the only kind of transaction available. For SQLite
version 2.8 and earlier, all transactions are exclusive.
</p>
<p>
The COMMIT command does not actually perform a commit until all
pending SQL commands finish. Thus if two or more SELECT statements