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2.0-Alpha-2 release (CVS 258)

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FossilOrigin-Name: d2a1aac46782c0d3852e34a3b32a6b2ccd93a256
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drh
2001-09-20 01:44:42 +00:00
parent 474d3d6156
commit 254cba2429
19 changed files with 361 additions and 526 deletions
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43
www/tclsqlite.tcl
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@ -1,7 +1,7 @@
#
# Run this Tcl script to generate the tclsqlite.html file.
#
set rcsid {$Id: tclsqlite.tcl,v 1.3 2000/10/23 13:16:33 drh Exp $}
set rcsid {$Id: tclsqlite.tcl,v 1.4 2001/09/20 01:44:44 drh Exp $}
puts {<html>
<head>
@ -44,27 +44,8 @@ way widgets are created in Tk.
</p>
<p>
The name of the database is usually either the name of a directory
that will contain the GDBM files that comprise the database, or it is the
name of the directory prefaced by "<b>gdbm:</b>". The second form
of the name is a new feature beginning in SQLite version 1.0.14 that
allows you to select alternative database backends. The default
backend is GDBM. But you can also select to store the database in
a hash table in memory by using the prefix "<b>memory:</b>".
Other backends may be added in the future.
</p>
<p>
Every time you open an SQLite database with the <b>memory:</b> prefix
on the database name, you get a new in-memory database. This is true
even if you open two databases with the same name. Furthermore,
an in-memory database is automatically deleted when the database is
closed and so is not useful for persistant storage like a normal
database. But the use of an in-memory SQL database does give Tcl/Tk
a powerful new data storage mechanism that can do things that are
difficult to do with only Tcl array variables. In fact, the
hash-table backend for SQLite was created for the sole purpose of
providing better data structure support to the Tcl language.
The name of the database is just the name of a disk file in which
the database is stored.
</p>
<p>
@ -229,19 +210,17 @@ will wait for locks to clear before giving up on a database transaction.
The default timeout is 0 millisecond. (In other words, the default behavior
is not to wait at all.)</p>
<p>The GDBM backend allows multiple simultaneous
<p>The SQlite database allows multiple simultaneous
readers or a single writer but not both. If any process is writing to
the database no other process is allows to read or write. If any process
is reading the database other processes are allowed to read but not write.
Each GDBM file is locked separately. Because each SQL table is stored as
a separate file, it is possible for different processes to write to different
database tables at the same time, just not the same table.</p>
The entire database shared a single lock.</p>
<p>When SQLite tries to open a GDBM file and finds that it is locked, it
<p>When SQLite tries to open a database and finds that it is locked, it
can optionally delay for a short while and try to open the file again.
This process repeats until the query times out and SQLite returns a
failure. The timeout is adjustable. It is set to 0 by default so that
if a GDBM file is locked, the SQL statement fails immediately. But you
if the database is locked, the SQL statement fails immediately. But you
can use the "timeout" method to change the timeout value to a positive
number. For example:</p>
@ -253,14 +232,14 @@ would be 2 seconds.</p>
<h2>The "busy" method</h2>
<p>The "busy" method, like "timeout", only comes into play when a GDBM
file is locked. But the "busy" method gives the programmer much more
<p>The "busy" method, like "timeout", only comes into play when the
database is locked. But the "busy" method gives the programmer much more
control over what action to take. The "busy" method specifies a callback
Tcl procedure that is invoked whenever SQLite tries to open a locked
GDBM file. This callback can do whatever is desired. Presumably, the
database. This callback can do whatever is desired. Presumably, the
callback will do some other useful work for a short while then return
so that the lock can be tried again. The callback procedure should
return "0" if it wants SQLite to try again to open the GDBM file and
return "0" if it wants SQLite to try again to open the database and
should return "1" if it wants SQLite to abandon the current operation.
}