📄 sysreq.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"><html><head><title>SQLite System Requirements</title><style type="text/css">body { margin: auto; font-family: "Verdana" "sans-serif"; padding: 8px 1%;}a { color: #45735f }a:visited { color: #734559 }.logo { position:absolute; margin:3px; }.tagline { float:right; text-align:right; font-style:italic; width:240px; margin:12px; margin-top:58px;}.toolbar { font-variant: small-caps; text-align: center; line-height: 1.6em; margin: 0; padding:1px 8px;}.toolbar a { color: white; text-decoration: none; padding: 6px 12px; }.toolbar a:visited { color: white; }.toolbar a:hover { color: #80a796; background: white; }.content { margin: 5%; }.content dt { font-weight:bold; }.content dd { margin-bottom: 25px; margin-left:20%; }.content ul { padding:0px; padding-left: 15px; margin:0px; }/* rounded corners */.se { background: url(images/se.png) 100% 100% no-repeat #80a796}.sw { background: url(images/sw.png) 0% 100% no-repeat }.ne { background: url(images/ne.png) 100% 0% no-repeat }.nw { background: url(images/nw.png) 0% 0% no-repeat }</style><meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head><body><div><!-- container div to satisfy validator --><a href="index.html"><img class="logo" src="images/SQLite.gif" alt="SQLite Logo" border="0"></a><div><!-- IE hack to prevent disappearing logo--></div><div class="tagline">Small. Fast. Reliable.<br>Choose any three.</div><table width=100% style="clear:both"><tr><td> <div class="se"><div class="sw"><div class="ne"><div class="nw"> <div class="toolbar"> <a href="about.html">About</a> <a href="sitemap.html">Sitemap</a> <a href="docs.html">Documentation</a> <a href="download.html">Download</a> <a href="copyright.html">License</a> <a href="news.html">News</a> <a href="http://www.sqlite.org/cvstrac/index">Developers</a> <a href="support.html">Support</a> </div></div></div></div></div></td></tr></table> <h1>System Requirements For SQLite</h1><p>This document outlines the high-level objectives of the SQLitelibrary.All of the features and capabilities of SQLite can be traced backto one of the requirements specified here.</p><p>SQLite is not a complete system and so the requirementsprovided by this document are not system requirements in thestrict sense. Perhaps "sub-system requirements" would be a betterterm, since SQLite is always a sub-component of a larger system.</p><p>This document is targeted primarily at developers who areworking within a waterfall development model that uses detailedrequirements written with the modal auxiliary verb "shall". However, this document is also useful as a general-purpose high-level description of SQLite for developers who are not working underdifferent development paradigms.</p><h2>1.0 SQLite is a translator from SQL into low-level disk I/O</h2><a name="S10000"></a><p> SQLite is an SQL database engine. And the fundamental task of every SQL database engine it to translate the abstract SQL statements readily understood by humans into sequences of I/O operations readily understood by computer hardware. This requirement expresses the essense of SQLite.</p><blockquote><b>S10000:</b> The SQLite library shall translate high-level SQL statements into low-level I/O calls to persistent storage.</blockquote><a name="S10100"></a><p> SQL is one of the worlds most widely known programming languages, but it is also one of the most ill-defined. There are various SQL standards documents available. However the SQL standards documents are obtuse to the point of being incomprehensible. And the standards allow for so much "implementation defined" behavior that there exist two SQL database engines understand exactly the same language.</p> <p>SQLite does not attempt to obtain strict compliance with any one of the various SQL standards. Instead, SQLite tries to be as compatible as possible with other SQL database engines. SQLite attempts to operate on the principle of least surprise. That is to say, experienced SQL programmers should find SQLite's dialect intuitive and natural.</p> <p>SQLite may omit some obscure features of SQLite. And the SQL dialect that SQLite understands might contain some enhancements not found in some standards documents. Nevertheless, applications written for other SQL database engines should be portable to SQLite with little to no change. And programmers writing code for SQLite should not encounter anything unexpected.</p><blockquote><b>S10100:</b> The SQLite library shall accepts a well-defined dialect of SQL that conforms to published SQL standards.</blockquote><a name="S10110"></a><p> SQLite is able to hold content in various datatypes and sizes.</p><blockquote><b>S10110:</b> The SQLite library shall support BLOB, CLOB, integer, and floating-point datatypes.</blockquote><a name="S10120"></a><p> SQLite handles NULLs in accordance with SQL standards. In cases where published standards are ambiguous, SQLite will follow the practice of other popular database engines.</p><blockquote><b>S10120:</b> The SQLite library shall implement the standard SQL interpretation of NULL values.</blockquote><a name="S10200"></a><p> Most other database engines implement a client/server model in which a small client library is linked with the application and the client communicates with a separate server process using interprocess communication (IPC). SQLite avoids the complication of having a separate server process by doing direct I/O directly to the underlying filesystem.</p><blockquote><b>S10200:</b> The SQLite library shall communicate directly with database files in persistent storage.</blockquote><a name="S10300"></a><p> In the database world, "ACID" is an acronym for Atomic, Consistent, Isolated, and Durable. Atomic means that a change to the database happens either entirely or not at all. Consistent means that if the database file is well-formed before the start of a transaction then it is guaranteed to be well-formed after the transaction commits. Isolated means that when two or more threads are processes are working with the same database, uncommitted changes made by one are not visible to the other. Durable means that once a transaction commits, it stays committed even if there is a subsequent software crash or power failure.</p><blockquote><b>S10300:</b> The SQLite library shall implement ACID transactions.</blockquote><a name="S10500"></a><p> An operating system crash or an unexpected power loss can sometimes damage the underlying persistent storage in ways that no software can defend against. (For example, the content of a disk drive might be completely erased and become unrecoverable.) Nevertheless, software can take steps to defend against the kinds of damage that typically occurs following operating system crashes and power failures. The usual damage is that some writes are missing or incomplete and that writes have occurred out of order. We say that software is "robust" if it defines against the common kinds of damage seen following an operating system crash or power loss.</p></p><blockquote><b>S10500:</b> The SQLite library shall implement transactions that are robust across application crashes, operating-system crashes, and power failures.</blockquote><a name="S10600"></a><p> Many applications benefit from being about to access multiple database file using the same database connection, so that information can be transfered from from one database to another atomically, or so that queries can join data across multiple databases.</p><blockquote><b>S10600:</b> The SQLite library shall support simultaneous access to multiple database files on the same database connection.</blockquote><a name="S10700"></a><p> A database is of little practical use if one is unable to obtain information from the database. Hence:</p><blockquote><b>S10700:</b> The SQLite library shall provide interfaces that allow the application to obtain the status and results of SQL operations.</blockquote><h2>2.0 SQLite is designed to be extensible by the application</h2><a name="S20000"></a><p> SQLite is intended to be an embedded database that functions well in resource-limited systems. For that reason we desire to keep the size of the library small. That choices argues against a large default function set. Instead of having many built-in features, SQLite is designed to be extensible at compile-time and run-time with new application-defined functions and behaviors.</p><blockquote><b>S20000:</b> The SQLite library shall be extensible and configurable.</blockquote><a name="S20100"></a><p> SQLite works on common workstations and in embedded systems. Sometimes these devices, particularly embedded systems, have odd and unusual operating systems. In order to support this level of portability, SQLite allows the interface to the operating system to be defined at run-time.</p><blockquote><b>S20100:</b> The SQLite library shall provide interfaces that permit the application to override interfaces to the platform on which the application is running.</blockquote><a name="S20110"></a><blockquote><b>S20110:</b> The SQLite library shall provide interfaces that permit the application to override the interfaces used to read and write persistent storage.</blockquote><a name="S20120"></a><blockquote><b>S20120:</b> The SQLite library shall provide interfaces that permit the application to override the interfaces used for memory allocation.</blockquote><a name="S20130"></a><blockquote><b>S20130:</b> The SQLite library shall provide interfaces that permit the application to override the interfaces used for controlling mutexes.</blockquote><a name="S20200"></a><p> Most SQL database engines support a rich set of SQL functions. SQLite, in contrast, supports only a select few SQL functions. But SQLite makes up for its dearth of built-in SQL functions by allowing the application to create new SQL function easily.</p><blockquote><b>S20200:</b> The SQLite library shall provide interfaces that permit the application to create new SQL functions.</blockquote><a name="S20300"></a><p> By default, SQLite only understands ASCII text. The tables needed to do proper comparisons and case folding of full unicode text are huge - much larger than the SQLite library itself. And, any application that is dealing with unicode already probably already has those tables built in. For SQLite to include unicode comparison tables would be redundant and wasteful. As a compromise, SQLite allows the application to specify alternative collating sequences for things such as unicode text, so that for applications that need such comparison sequences can have them easily while other applications that are content with ASCII are not burdened with unnecessary tables.</p><blockquote><b>S20300:</b> The SQLite library shall provide interfaces that permit the application to create new text collating sequences.</blockquote><a name="S20400"></a><p> A virtual table is an SQL object that appears to be an ordinary SQL table for the purposes of INSERT, UPDATE, DELETE, and SELECT statements. But instead of being backed by persistent storage, the virtual table is an object that responds programmatically to INSERT, UPDATE, DELETE, and SELECT requests. Virtual tables have been used to implement full-text search and R-Tree indices, among other things.</p><blockquote><b>S20400:</b> The SQLite library shall provide interfaces that permit the application to create new classes of virtual SQL tables.</blockquote><a name="S20500"></a><p> Some applications choose to package extensions in separate shared library files and load those extensions at run-time on an as-needed basis. Depending on the nature of the application, this can be an aid to configuration management, since it allows the extension to be updated without having to replace the core application.</p><blockquote><b>S20500:</b> The SQLite library shall provide interfaces that permit the application to load extensions at run-time using shared libraries.</blockquote><a name="S20600"></a><p> SQLite has finite limits. For example, there is a maximum size BLOB or CLOB that SQLite will store, a maximum size to a database file, a maximum number of columns in a table or query, and a maximum depth of an expression parse tree. All of these have default values that are sufficiently large that a typical application is very unlikely to ever reach the limits. But some applications (for example, applications that process content from untrusted and possibly hostile sources) might want to define much lower limits on some database connections for the purpose of preventing denial-of-service attacks. Or, an application might want to select much lower limits in order to prevent over-utilization of limited resources on an embedded device. Whatever the rationale, SQLite permits limits to be queried and set at run-time.</p><blockquote><b>S20600:</b> The SQLite library shall provide interfaces that permit the application to dynamically query and modify size limits.</blockquote><h2>3.0 SQLite is lightweight and leak-free</h2>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -