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Diffstat (limited to 'www/arch.tcl')
| -rw-r--r-- | www/arch.tcl | 29 |
1 files changed, 17 insertions, 12 deletions
diff --git a/www/arch.tcl b/www/arch.tcl index b4b63c3ad..cafabb5ec 100644 --- a/www/arch.tcl +++ b/www/arch.tcl @@ -1,7 +1,7 @@ # # Run this Tcl script to generate the sqlite.html file. # -set rcsid {$Id: arch.tcl,v 1.3 2000/09/29 13:30:55 drh Exp $} +set rcsid {$Id: arch.tcl,v 1.4 2001/09/16 00:13:29 drh Exp $} puts {<html> <head> @@ -112,19 +112,24 @@ source file <b>vdbe.c</b>. The virtual machine also has its own header file <b>vdbe.h</b> that defines an interface between the virtual machine and the rest of the SQLite library.</p> -<h2>Backend</h2> +<h2>B-tree Driver</h2> -<p>The last layer in the design of SQLite is the backend. The -backend implements an interface between the virtual machine and -the underlying data file library -- GDBM in this case. The interface -is designed to make it easy to substitute a different database -library, such as the Berkeley DB. -The backend abstracts many of the low-level details to help -reduce the complexity of the virtual machine.</p> +<p>An SQLite database is maintained on disk using a B-tree implementation +found in the <b>btree.c</b> source file. A separate B-tree is used for +each table and index in the database but all B-trees are stored in the +same disk file. Each page of a B-tree is 1024 bytes in size. The data +is stored with the key in an area called "payload". Up to 236 bytes of +payload can be stored with each B-tree entry. Any additional payload +is stored in a chain of overflow pages.</p> -<p>The backend is contained in the single source file <b>dbbe.c</b>. -The backend also has a header file <b>dbbe.h</b> that defines the -interface between the backend and the rest of the SQLite library.</p> +<h2>Page Cache</h2> + +<p>The page cache provides the rollback and atomic commit abstraction +and takes care of reader/writer locking of the database file. The +B-tree driver requests particular pages from the page cache and notifies +the page cache when it wants to modify pages and commit or rollback its +changes and the page cache handles all the messy details of making sure +the requests are handled quickly, safely, and efficiently.</p> } puts { |