Skip to content

H
h2database
切换分支/标签
查找文件
Normal viewHistoryPermalink
architecture.html 5.3 KB
Newer Older
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
1 2 
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!--
Evgenij Ryazanov's avatar
Update years in copyright headers
0bc00191
 
Evgenij Ryazanov committed
3 
Copyright 2004-2018 H2 Group. Multiple-Licensed under the MPL 2.0, Version 1.0,
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
4 5 6 7 
and under the Eclipse Public License, Version 1.0
Initial Developer: H2 Group
-->
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
Thomas Mueller's avatar
Documentation (add "viewport")
f504aaa1
 
Thomas Mueller committed
8 9 
<head>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
Thomas Mueller's avatar
Documentation
fe2cf166
 
Thomas Mueller committed
10 
<meta name="viewport" content="width=device-width, initial-scale=1" />
Thomas Mueller's avatar
Documentation (add "viewport")
f504aaa1
 
Thomas Mueller committed
11 
<title>
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
12 
Architecture
Thomas Mueller's avatar
Documentation (add "viewport")
f504aaa1
 
Thomas Mueller committed
13 14 
</title>
<link rel="stylesheet" type="text/css" href="stylesheet.css" />
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 
<!-- [search] { -->
<script type="text/javascript" src="navigation.js"></script>
</head><body onload="frameMe();">
<table class="content"><tr class="content"><td class="content"><div class="contentDiv">
<!-- } -->

<h1>Architecture</h1>
<a href="#introduction">
    Introduction</a><br />
<a href="#top_down">
    Top-down overview</a><br />
<a href="#jdbc">
    JDBC driver</a><br />
<a href="#connection">
    Connection/session management</a><br />
<a href="#command">
    Command execution and planning</a><br />
<a href="#table">
Thomas Mueller's avatar
Fix formatting
1370b8c5
 
Thomas Mueller committed
33 
    Table/index/constraints</a><br />
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
34 
<a href="#transaction">
Thomas Mueller's avatar
Documentation / spellchecker
aea17cdf
 
Thomas Mueller committed
35 
    Undo log, redo log, and transactions layer</a><br />
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 
<a href="#btree">
    B-tree engine and page-based storage allocation</a><br />
<a href="#filesystem">
    Filesystem abstraction</a><br />

<h2 id="introduction">Introduction</h2>
<p>
H2 implements an embedded and standalone ANSI-SQL89 compliant SQL engine on top of a B-tree based disk store.
</p>
<p>
As of October 2013, Thomas is still working on our next-generation storage engine called MVStore. This will
in time replace the B-tree based storage engine.
</p>

<h2 id="top_down">Top-down Overview</h2>
<p>
Working from the top down, the layers look like this:
Thomas Mueller's avatar
Fix formatting
1370b8c5
 
Thomas Mueller committed
53 54 55 56 57 
<ul><li>JDBC driver.
</li><li>Connection/session management.
</li><li>SQL Parser.
</li><li>Command execution and planning.
</li><li>Table/Index/Constraints.
Thomas Mueller's avatar
Documentation / spellchecker
aea17cdf
 
Thomas Mueller committed
58 
</li><li>Undo log, redo log, and transactions layer.
Thomas Mueller's avatar
Fix formatting
1370b8c5
 
Thomas Mueller committed
59 60 61 
</li><li>B-tree engine and page-based storage allocation.
</li><li>Filesystem abstraction.
</li></ul>
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 
</p>

<h2 id="jdbc">JDBC Driver</h2>
<p>
The JDBC driver implementation lives in <code>org.h2.jdbc, org.h2.jdbcx</code>
</p>

<h2 id="connection">Connection/session management</h2>
<p>
The primary classes of interest are:
<table class="main">
<tr><th>Package</th><th>Description</th></tr>
<tr><td>org.h2.engine.Database</td><td>the root/global class</td></tr>
<tr><td>org.h2.engine.SessionInterface</td>
    <td>abstracts over the differences between embedded and remote sessions</td></tr>
<tr><td>org.h2.engine.Session</td>
    <td>local/embedded session</td></tr>
<tr><td>org.h2.engine.SessionRemote</td>
    <td>remote session</td></tr>
</table>
</p>

<h2 id="jdbc">Parser</h2>
<p>
The parser lives in <code>org.h2.command.Parser</code>. It uses a straightforward recursive-descent design.
</p>
<p>
See Wikipedia <a href="http://en.wikipedia.org/wiki/Recursive_descent_parser">Recursive-descent parser</a> page.
</p>


<h2 id="command">Command execution and planning</h2>
<p>
Unlike other databases, we do not have an intermediate step where we generate some kind of IR (intermediate representation) of the query.
The parser class directly generates a command execution object.
Then we run some optimisation steps over the command to possibly generate a more efficient command.

The primary packages of interest are:
<table class="main">
<tr><th>Package</th><th>Description</th></tr>
<tr><td>org.h2.command.ddl</td><td>Commands that modify schema data structures</td></tr>
<tr><td>org.h2.command.dml</td><td>Commands that modify data</td></tr>
</table>
</p>

<h2 id="table">Table/Index/Constraints</h2>
<p>
One thing to note here is that indexes are simply stored as special kinds of tables.
</p>
<p>
The primary packages of interest are:
<table class="main">
<tr><th>Package</th><th>Description</th></tr>
<tr><td>org.h2.table</td><td>Implementations of different kinds of tables</td></tr>
<tr><td>org.h2.index</td><td>Implementations of different kinds of indices</td></tr>
</table>
</p>
Thomas Mueller's avatar
Documentation / spellchecker
aea17cdf
 
Thomas Mueller committed
120 
<h2 id="transaction">Undo log, redo log, and transactions layer</h2>
noelgrandin's avatar
first stage of generating some architecture documentation
fa2a6925
 
noelgrandin committed
121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 
<p>
We have a transaction log, which is shared among all sessions. See also
http://en.wikipedia.org/wiki/Transaction_log
http://h2database.com/html/grammar.html#set_log
</p>
<p>
We also have an undo log, which is per session, to undo an operation (an update that fails for example)
and to rollback a transaction.
Theoretically, the transaction log could be used, but for simplicity, H2 currently uses it's
own "list of operations" (usually in-memory).
</p>
<p>
With the MVStore, this is no longer needed (just the transaction log).
</p>

<h2 id="btree">B-tree engine and page-based storage allocation.</h2>
<p>
The primary package of interest is <code>org.h2.store</code>.
</p>
<p>
This implements a storage mechanism which allocates pages of storage (typically 2k in size)
and also implements a b-tree over those pages to allow fast retrieval and update.
</p>

<h2 id="filesystem">Filesystem abstraction.</h2>
<p>
The primary class of interest is <code>org.h2.store.FileStore</code>.
</p>
<p>
This implements an abstraction of a random-access file.
This allows the higher layers to treat in-memory vs. on-disk vs. zip-file databases the same.
</p>

<!-- [close] { --></div></td></tr></table><!-- } --><!-- analytics --></body></html>