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This article mainly explains "what are the changes in SQLite4 design". The content in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what are the changes in SQLite4 design?"

1.0 content summary

SQLite4 is a compact, self-contained, zero-maintenance ACID database engine placed in a library, like SQLite3, but with improved interfaces and file formats.

The runtime environment is encapsulated into an object.

A good key-value pair storage engine is used:

A separate large key space-not a separate key space and index for each table in SQLite3.

Sort by key in dictionary order.

Multiple storage engines that can be interchangeable at run time.

The default storage on disk gallantly uses a log structure of the merged database.

The PRIMARY KEY of the table is actually used as the key of the storage engine.

You can use the decimal point operation.

Foreign key constraints and recursive triggers are enabled by default.

The coverage index can display a statement.

2.0 Overview

SQLite4 is an option, not an alternative, for SQLite3. SQLite3 is not out of date. SQLite3 and QLite4 will be supported in parallel. The benefits left by SQLite3 will not be abandoned. SQLite3 will also be continuously maintained and improved. But if necessary, designers of the new system will now be able to choose SQLite4 over SQLite3.

SQLite4 strives to maintain the best features of SQLite3 and solves the irreparable problems in SQLite3 without breaking compatibility. The same features that will remain the same in SQLite3 and SQLite4 are:

SQLite4 is a complete, relational, transactional, ACID, SQL database engine that is placed in a library and linked to a large application. There is no server, IWeiO faces the hard disk directly.

SQLite4 source code anyone can be used for any purpose. There are no restrictions on copyright, publishing or releasing source code or compiling binaries. You don't have to worry about annoying permits.

Dynamic types are used instead of the rigid static types used by most other SQL database engines.

The (default) image on disk is a separate disk file that uses a good and stable file format, making the SQLite4 library suitable for use as an application file format.

SQLite4 will be fast and reliable, and it will work well without the administrator's worry.

The implementation of SQLite4 has only the simplest dependency, so it can be easily integrated into embedded systems or other unconventional runtime environments.

The common assembly language C is still used in the implementation. SQLite4 uses more C99 features than SQLite3, but it can still be compiled using a common compiler. SQLite4 uses standard data types such as size_t,int64_t,uint64_t and other data types.

The programming interface of SQLite4 is very similar to that of SQLite3, except that the naming prefix is changed from sqlite3_ to sqlite4_. The old and obsolete interfaces in SQLite3 have been removed from SQLite4. Add parameters to some functions, sometimes slightly modify the parameters or reorder the parameters. Some interface names have been modified to make them more in line with their functions. In general, the programming interface of SQLite4 is very similar to that of SQLite3, so it only takes an hour or two to search for alternatives to port an application on SQLite3 to SQLite4.

SQLite3 and SQLite4 do not share any symbols, so it is feasible to embed SQLite3 and SQLite4 into the same process at the same time.

Major changes to 3.0 SQLite4

3.1 Runtime objects

The first parameter of some interfaces in SQLite4 receives a (newly added) pointer to a sqlite4_env object that defines the runtime environment. Sample programs that need to receive sqlite4_env pointers include:

Sqlite4_open ()

Sqlite4_malloc (), sqlite4_realloc (), and sqlite4_free ()

Sqlite4_mprintf ()

Sqlite4_random ()

Sqlite4_config ()

An instance of a sqlite4_env object defines how SQLite4 interacts with other systems. A sqlite4_env object contains methods that can:

Assign, enter, leave and reclaim the mutex

Allocate, adjust, and free heap memory

Access and control the underlying key / value storage engine

Initialize built-in PRNG with high-quality random seeds

Get the current time and date and local time zone

Log error log messages.

The SQLite4 build of the standard platform (windows and Unix) contains a global sqlite4_env object, which is usually appropriate for the platform. If an interface program has a pointer to a sqlite4_env object in its parameter, and the pointer passed to that parameter is a null pointer, the interface program will use the default global sqlite4_env object. In addition, some applications may require two or more SQLite4 instances to run on the same address space, while each instance uses its own different mutex primitive, different memory heap, different time and date functions, and so on. SQLite4 meets this requirement by creating different sqlite4_env objects for each database instance. Global and static variables are also abolished in the sqlite4_env object, making it very easy to port SQLite4 to embedded systems that provide limited support for static or global data.

3.2 simplified key / value storage engine

It has a greatly simplified interface compared to the key / value storage engine used by SQLite3,SQLite4. The storage engine is pluggable; it can be changed at run time by making appropriate changes to the qlite4_env object before opening a new database connection.

SQLite4 needs a storage engine that implements ordered key / value pairs whose keys and values are binary data of any length. The keys must be unique and sorted by dictionary. That is, the keys should be sorted according to a comparison function, for example:

The copy code is as follows:

Int key_compare (const void * key1, int N1, const void * key2, int N2) {

Int c = memcmp (key1, key2, N1)

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