File Format Changes in SQLite

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File Format Changes in SQLite

The underlying file format for SQLite databases does not change in incompatible ways. There are literally hundreds of billions, perhaps trillions, of SQLite database files in circulation and the SQLite developers are committing to supporting those files for decades into the future.

This document describes incompatibilities that have occurred in SQLite prior to 2004. Since 2004, there have been enhancements to SQLite such that newer database files are unreadable by older versions of the SQLite library. But the most recent versions of the SQLite library should be able to read and write any older SQLite database file without any problems.

In other words, since 2004 all SQLite releases have been backwards compatible, though not necessarily forwards compatible.

The following table summarizes the SQLite file format changes that have occurred since version 1.0.0:

Version Change Approx. Date Description Of File Format Change

1.0.32 to 2.0.0 2001-09-20 Version 1.0.X of SQLite used the GDBM library as its backend interface to the disk. Beginning in version 2.0.0, GDBM was replaced by a custom B-Tree library written especially for SQLite. The new B-Tree backend is twice as fast as GDBM, supports atomic commits and rollback, and stores an entire database in a single disk file instead using a separate file for each table as GDBM does. The two file formats are not even remotely similar.

2.0.8 to 2.1.0 2001-10-12 The same basic B-Tree format is used but the details of the index keys were changed in order to provide better query optimization opportunities. Some of the headers were also changed in order to increase the maximum size of a row from 64KB to 24MB.
This change is an exception to the version number rule described above in that it is neither forwards or backwards compatible. A complete reload of the database is required. This is the only exception.

2.1.7 to 2.2.0 2001-12-21 Beginning with version 2.2.0, SQLite no longer builds an index for an INTEGER PRIMARY KEY column. Instead, it uses that column as the actual B-Tree key for the main table.
Version 2.2.0 and later of the library will automatically detect when it is reading a 2.1.x database and will disable the new INTEGER PRIMARY KEY feature. In other words, version 2.2.x is backwards compatible to version 2.1.x. But version 2.1.x is not forward compatible with version 2.2.x. If you try to open a 2.2.x database with an older 2.1.x library and that database contains an INTEGER PRIMARY KEY, you will likely get a coredump. If the database schema does not contain any INTEGER PRIMARY KEYs, then the version 2.1.x and version 2.2.x database files will be identical and completely interchangeable.

2.2.5 to 2.3.0 2002-01-30 Beginning with version 2.3.0, SQLite supports some additional syntax (the "ON CONFLICT" clause) in the CREATE TABLE and CREATE INDEX statements that are stored in the SQLITE_MASTER table. If you create a database that contains this new syntax, then try to read that database using version 2.2.5 or earlier, the parser will not understand the new syntax and you will get an error. Otherwise, databases for 2.2.x and 2.3.x are interchangeable.

2.3.3 to 2.4.0 2002-03-10 Beginning with version 2.4.0, SQLite added support for views. Information about views is stored in the SQLITE_MASTER table. If an older version of SQLite attempts to read a database that contains VIEW information in the SQLITE_MASTER table, the parser will not understand the new syntax and initialization will fail. Also, the way SQLite keeps track of unused disk blocks in the database file changed slightly. If an older version of SQLite attempts to write a database that was previously written by version 2.4.0 or later, then it may leak disk blocks.

2.4.12 to 2.5.0 2002-06-17 Beginning with version 2.5.0, SQLite added support for triggers. Information about triggers is stored in the SQLITE_MASTER table. If an older version of SQLite attempts to read a database that contains a CREATE TRIGGER in the SQLITE_MASTER table, the parser will not understand the new syntax and initialization will fail.

2.5.6 to 2.6.0 2002-07-17 A design flaw in the layout of indices required a file format change to correct. This change appeared in version 2.6.0.
If you use version 2.6.0 or later of the library to open a database file that was originally created by version 2.5.6 or earlier, an attempt to rebuild the database into the new format will occur automatically. This can take some time for a large database. (Allow 1 or 2 seconds per megabyte of database under Unix - longer under Windows.) This format conversion is irreversible. It is strongly suggested that you make a backup copy of older database files prior to opening them with version 2.6.0 or later of the library, in case there are errors in the format conversion logic.
Version 2.6.0 or later of the library cannot open read-only database files from version 2.5.6 or earlier, since read-only files cannot be upgraded to the new format.

2.6.3 to 2.7.0 2002-08-13
Beginning with version 2.7.0, SQLite understands two different datatypes: text and numeric. Text data sorts in memcmp() order. Numeric data sorts in numerical order if it looks like a number, or in memcmp() order if it does not.

When SQLite version 2.7.0 or later opens a 2.6.3 or earlier database, it assumes all columns of all tables have type "numeric". For 2.7.0 and later databases, columns have type "text" if their datatype string contains the substrings "char" or "clob" or "blob" or "text". Otherwise they are of type "numeric".

Because "text" columns have a different sort order from numeric, indices on "text" columns occur in a different order for version 2.7.0 and later database. Hence version 2.6.3 and earlier of SQLite will be unable to read a 2.7.0 or later database. But version 2.7.0 and later of SQLite will read earlier databases.

2.7.6 to 2.8.0 2003-02-14
Version 2.8.0 introduces a change to the format of the rollback journal file. The main database file format is unchanged. Versions 2.7.6 and earlier can read and write 2.8.0 databases and vice versa. Version 2.8.0 can rollback a transaction that was started by version 2.7.6 and earlier. But version 2.7.6 and earlier cannot rollback a transaction started by version 2.8.0 or later.

The only time this would ever be an issue is when you have a program using version 2.8.0 or later that crashes with an incomplete transaction, then you try to examine the database using version 2.7.6 or earlier. The 2.7.6 code will not be able to read the journal file and thus will not be able to rollback the incomplete transaction to restore the database.

2.8.14 to 3.0.0 2004-06-18
Version 3.0.0 is a major upgrade for SQLite that incorporates support for UTF-16, BLOBs, and a more compact encoding that results in database files that are typically 25% to 50% smaller. The new file format is very different and is completely incompatible with the version 2 file format.

Version Change	Approx. Date	Description Of File Format Change
1.0.32 to 2.0.0	2001-09-20	Version 1.0.X of SQLite used the GDBM library as its backend interface to the disk. Beginning in version 2.0.0, GDBM was replaced by a custom B-Tree library written especially for SQLite. The new B-Tree backend is twice as fast as GDBM, supports atomic commits and rollback, and stores an entire database in a single disk file instead using a separate file for each table as GDBM does. The two file formats are not even remotely similar.
2.0.8 to 2.1.0	2001-10-12	The same basic B-Tree format is used but the details of the index keys were changed in order to provide better query optimization opportunities. Some of the headers were also changed in order to increase the maximum size of a row from 64KB to 24MB. This change is an exception to the version number rule described above in that it is neither forwards or backwards compatible. A complete reload of the database is required. This is the only exception.
2.1.7 to 2.2.0	2001-12-21	Beginning with version 2.2.0, SQLite no longer builds an index for an INTEGER PRIMARY KEY column. Instead, it uses that column as the actual B-Tree key for the main table. Version 2.2.0 and later of the library will automatically detect when it is reading a 2.1.x database and will disable the new INTEGER PRIMARY KEY feature. In other words, version 2.2.x is backwards compatible to version 2.1.x. But version 2.1.x is not forward compatible with version 2.2.x. If you try to open a 2.2.x database with an older 2.1.x library and that database contains an INTEGER PRIMARY KEY, you will likely get a coredump. If the database schema does not contain any INTEGER PRIMARY KEYs, then the version 2.1.x and version 2.2.x database files will be identical and completely interchangeable.
2.2.5 to 2.3.0	2002-01-30	Beginning with version 2.3.0, SQLite supports some additional syntax (the "ON CONFLICT" clause) in the CREATE TABLE and CREATE INDEX statements that are stored in the SQLITE_MASTER table. If you create a database that contains this new syntax, then try to read that database using version 2.2.5 or earlier, the parser will not understand the new syntax and you will get an error. Otherwise, databases for 2.2.x and 2.3.x are interchangeable.
2.3.3 to 2.4.0	2002-03-10	Beginning with version 2.4.0, SQLite added support for views. Information about views is stored in the SQLITE_MASTER table. If an older version of SQLite attempts to read a database that contains VIEW information in the SQLITE_MASTER table, the parser will not understand the new syntax and initialization will fail. Also, the way SQLite keeps track of unused disk blocks in the database file changed slightly. If an older version of SQLite attempts to write a database that was previously written by version 2.4.0 or later, then it may leak disk blocks.
2.4.12 to 2.5.0	2002-06-17	Beginning with version 2.5.0, SQLite added support for triggers. Information about triggers is stored in the SQLITE_MASTER table. If an older version of SQLite attempts to read a database that contains a CREATE TRIGGER in the SQLITE_MASTER table, the parser will not understand the new syntax and initialization will fail.
2.5.6 to 2.6.0	2002-07-17	A design flaw in the layout of indices required a file format change to correct. This change appeared in version 2.6.0. If you use version 2.6.0 or later of the library to open a database file that was originally created by version 2.5.6 or earlier, an attempt to rebuild the database into the new format will occur automatically. This can take some time for a large database. (Allow 1 or 2 seconds per megabyte of database under Unix - longer under Windows.) This format conversion is irreversible. It is strongly suggested that you make a backup copy of older database files prior to opening them with version 2.6.0 or later of the library, in case there are errors in the format conversion logic. Version 2.6.0 or later of the library cannot open read-only database files from version 2.5.6 or earlier, since read-only files cannot be upgraded to the new format.
2.6.3 to 2.7.0	2002-08-13	Beginning with version 2.7.0, SQLite understands two different datatypes: text and numeric. Text data sorts in memcmp() order. Numeric data sorts in numerical order if it looks like a number, or in memcmp() order if it does not. When SQLite version 2.7.0 or later opens a 2.6.3 or earlier database, it assumes all columns of all tables have type "numeric". For 2.7.0 and later databases, columns have type "text" if their datatype string contains the substrings "char" or "clob" or "blob" or "text". Otherwise they are of type "numeric". Because "text" columns have a different sort order from numeric, indices on "text" columns occur in a different order for version 2.7.0 and later database. Hence version 2.6.3 and earlier of SQLite will be unable to read a 2.7.0 or later database. But version 2.7.0 and later of SQLite will read earlier databases.
2.7.6 to 2.8.0	2003-02-14	Version 2.8.0 introduces a change to the format of the rollback journal file. The main database file format is unchanged. Versions 2.7.6 and earlier can read and write 2.8.0 databases and vice versa. Version 2.8.0 can rollback a transaction that was started by version 2.7.6 and earlier. But version 2.7.6 and earlier cannot rollback a transaction started by version 2.8.0 or later. The only time this would ever be an issue is when you have a program using version 2.8.0 or later that crashes with an incomplete transaction, then you try to examine the database using version 2.7.6 or earlier. The 2.7.6 code will not be able to read the journal file and thus will not be able to rollback the incomplete transaction to restore the database.
2.8.14 to 3.0.0	2004-06-18	Version 3.0.0 is a major upgrade for SQLite that incorporates support for UTF-16, BLOBs, and a more compact encoding that results in database files that are typically 25% to 50% smaller. The new file format is very different and is completely incompatible with the version 2 file format.