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Why Is SQLite Coded In C
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<a onclick="toggle_toc()">
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<span class="fancy_toc_mark" id="toc_mk">►</span>
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Table Of Contents
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</a>
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<div id="toc_sub"><div class="fancy-toc1"><a href="#c_is_best">1. C Is Best</a></div>
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<div class="fancy-toc2"><a href="#performance">1.1. Performance</a></div>
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<div class="fancy-toc2"><a href="#compatibility">1.2. Compatibility</a></div>
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<div class="fancy-toc2"><a href="#low_dependency">1.3. Low-Dependency</a></div>
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<div class="fancy-toc2"><a href="#stability">1.4. Stability</a></div>
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<div class="fancy-toc1"><a href="#why_isn_t_sqlite_coded_in_an_object_oriented_language_">2. Why Isn't SQLite Coded In An Object-Oriented Language?</a></div>
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<div class="fancy-toc1"><a href="#why_isn_t_sqlite_coded_in_a_safe_language_">3. Why Isn't SQLite Coded In A "Safe" Language?</a></div>
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<h1 id="c_is_best"><span>1. </span>C Is Best</h1>
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<blockquote><table border="'1'"><tr><td>
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Note: Sections 2.0 and 3.0 of this article were added in response
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to comments on
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<a href="https://news.ycombinator.com/item?id=16585120">Hacker News</a> and
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<a href="https://www.reddit.com/r/programming/comments/84fzoc/why_is_sqlite_coded_in_c/">Reddit</a>.
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</td></tr></table></blockquote>
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<p>
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Since its inception on 2000-05-29, SQLite has been implemented in generic C.
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C was and continues to be the best language for implementing a software
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library like SQLite. There are no plans to recode SQLite in any other
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programming language at this time.
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</p><p>
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The reasons why C is the best language to implement SQLite include:
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</p><ul>
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<li> Performance
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</li><li> Compatibility
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</li><li> Low-dependency
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</li><li> Stability
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</li></ul>
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<h2 id="performance"><span>1.1. </span>Performance</h2>
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<p>An intensively used low-level library like SQLite needs to be fast.
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(And SQLite is fast, see <a href="intern-v-extern-blob.html">Internal Versus External BLOBs</a> and
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<a href="fasterthanfs.html">35% Faster Than The Filesystem</a> for example.)
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</p><p>C is a great language for writing fast code. C is sometimes
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described as "portable assembly language". It enables to developers
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to code as close to the underlying hardware as possible while still
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remaining portable across platforms.
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</p><p>Other programming languages sometimes claim to be "as fast as C".
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But no other language claims to be faster than C for general-purpose
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programming, because none are.
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</p><h2 id="compatibility"><span>1.2. </span>Compatibility</h2>
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<p>Nearly all systems have the ability to call libraries
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written in C. This is not true of other implementation languages.
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</p><p>So, for example, Android applications written in Java are able to
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invoke SQLite (through an adaptor). Maybe it would have been more
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convenient for Android if SQLite had been coded in Java as that would
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make the interface simpler. However, on iPhone applications are coded
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in Objective-C or Swift, neither of which have the ability to call
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libraries written in Java. Thus, SQLite would be unusable on iPhones
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had it been written in Java.
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</p><h2 id="low_dependency"><span>1.3. </span>Low-Dependency</h2>
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<p>Libraries written in C do not have a huge run-time dependency.
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In its minimum configuration, SQLite requires only the following
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routines from the standard C library:
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</p><center>
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<table border="0">
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<tr>
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<td valign="top">
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<ul>
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<li> memcmp()
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</li><li> memcpy()
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</li><li> memmove()
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</li><li> memset()
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</li></ul>
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</td>
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<td> </td>
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<td valign="top">
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<ul>
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<li> strcmp()
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</li><li> strlen()
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</li><li> strncmp()
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</li></ul>
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</td>
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</tr>
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</table>
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</center>
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<p>
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In a more complete build, SQLite also uses library routines like
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malloc() and free() and operating system interfaces for opening, reading,
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writing, and closing files. But even then, the number of dependencies
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is very small. Other "modern" language, in contrast, often require
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multi-megabyte runtimes loaded with thousands and thousands of interfaces.
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</p><h2 id="stability"><span>1.4. </span>Stability</h2>
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<p>
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The C language is old and boring.
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It is a well-known and well-understood language.
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This is exactly what one wants when developing a module like SQLite.
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Writing a small, fast, and reliable database engine is hard enough as it
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is without the implementation language changing out from under you with
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each update to the implementation language specification.
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</p><h1 id="why_isn_t_sqlite_coded_in_an_object_oriented_language_"><span>2. </span>Why Isn't SQLite Coded In An Object-Oriented Language?</h1>
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<p>
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Some programmers cannot imagine developing a complex system like
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SQLite in a language that is not "object oriented". So why is
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SQLite not coded in C++ or Java?
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</p><ol>
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<li><p>
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Libraries written in C++ or Java can generally only be used by
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applications written in the same language. It is difficult to
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get an application written in Haskell or Java to invoke a library
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written in C++. On the other hand, libraries written in C are
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callable from any programming language.
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</p></li><li><p>
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Object-Oriented is a design pattern, not a programming language.
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You can do object-oriented programming in any language you want,
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including assembly language. Some languages (ex: C++ or Java) make
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object-oriented easier. But you can still do object-oriented programming
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in languages like C.
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</p></li><li><p>
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Object-oriented is not the only valid design pattern.
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Many programmers have been taught to think purely in terms of
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objects. And, to be fair, objects are often a good way to
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decompose a problem. But objects are not the only way, and are
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not always the best way to decompose a problem. Sometimes good old
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procedural code is easier to write, easier to maintain and understand,
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and faster than object-oriented code.
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</p></li><li><p>
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When SQLite was first being developed, Java was a young and immature
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language. C++ was older, but was undergoing such growing pains that
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it was difficult to find any two C++ compilers that worked the same
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way. So C was definitely a better choice back when SQLite was first
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being developed. The situation is less stark now, but there is little
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to no benefit in recoding SQLite at this point.
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</p></li></ol>
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<h1 id="why_isn_t_sqlite_coded_in_a_safe_language_"><span>3. </span>Why Isn't SQLite Coded In A "Safe" Language?</h1>
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<p>
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There has lately been a lot of interest in "safe" programming languages
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like Rust or Go in which it is impossible, or is at least difficult, to make
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common programming errors like memory leaks or array overruns. So the
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question often arises as to why SQLite is not coded in a "safe" language.
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</p><ol>
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<li><p>
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None of the safe programming languages existed for the first 10 years
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of SQLite's existence. SQLite could be recoded in Go or Rust, but doing
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so would probably introduce far more bugs than would be fixed, and it
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seems also likely to result in slower code.
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</p></li><li><p>
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Safe programming languages solve the easy problems: memory leaks,
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use-after-free errors, array overruns, etc. Safe languages provide
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no help beyond ordinary C code in solving the rather more difficult
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problem of computing a correct answer to an SQL statement.
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</p></li><li><p>
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Safe languages are often touted for helping to prevent
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security vulnerabilities. True enough, but SQLite is
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not a particularly security-sensitive library. If an application is
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running untrusted and unverified SQL, then it already has much bigger
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security issues (SQL injection) that no "safe" language will fix.
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</p><p>
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It is true that applications sometimes import complete binary SQLite
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database files from untrusted sources, and such imports could present a
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possible attack vector. However, those code paths in SQLite are
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limited and are extremely well tested. And pre-validation routines
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are available to applications that want to read untrusted databases
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that can help detect possible attacks prior to use.
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</p></li><li><p>
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Some "safe" languages (ex: Go) dislike the use of assert(). But
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the use of assert() is a vital part of keeping SQLite maintainable.
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The lack of assert() in Go is a show-stopper as far as the developers
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of SQLite are concerned. See the <a href="assert.html">The Use Of assert() In SQLite</a>
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article for additional information.
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</p></li><li><p>
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Safe languages insert additional machine branches to do things like
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verify that array accesses are in-bounds. In correct code, those
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branches are never taken. That means that the machine code cannot
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be 100% branch tested, which is an important component of SQLite's
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quality strategy.
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</p></li><li><p>
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Safe languages usually want to abort if they encounter an out-of-memory
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(OOM) situation. SQLite is designed to recover gracefully from an OOM.
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It is unclear how this could be accomplished in the current crop of
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safe languages.
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</p></li><li><p>
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All of the existing safe languages are new. The developers of SQLite
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applaud the efforts of computer language researchers in trying to
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develop languages that are easier to program safely. We encourage these
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efforts to continue. Be we ourselves are more interested in old and
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boring languages when it comes to implementing SQLite.
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</p></li></ol>
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<p>
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All that said, it is possible that SQLite might
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one day be recoded in Rust. Recoding SQLite in Go is unlikely
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since Go hates assert(). But Rust is a possibility. Some
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preconditions that must occur before SQLite is recoded in Rust
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include:
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</p><p>
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</p><ol type="A">
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<li> Rust needs to mature a little more, stop changing so fast, and
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move further toward being old and boring.
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</li><li> Rust needs to demonstrate that it can be used to create general-purpose
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libraries that are callable from all other programming languages.
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</li><li> Rust needs to demonstrate that it can produce object code that
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works on obscure embedded devices, including devices that lack
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an operating system.
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</li><li> Rust needs to pick up the necessary tooling that enables one to
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do 100% branch coverage testing of the compiled binaries.
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</li><li> Rust needs a mechanism to recover gracefully from OOM errors.
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</li><li> Rust needs to demonstrate that it can do the kinds of work that
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C does in SQLite without a significant speed penalty.
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</li></ol>
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<p>
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If you are a "rustacean" and feel that Rust already meets the
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preconditions listed above, and that SQLite should be recoded in
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Rust, then you are welcomed and encouraged
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to contact the SQLite developers privately
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and argue your case.
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</p>
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