H2database - Revision history

MihaiPopa7: Fixed syntax.

2023-09-17T18:02:54Z

Fixed syntax.

Ross-spencer: Add some information about versioning

2023-09-17T15:30:51Z

Add some information about versioning

Ross-spencer at 10:42, 17 September 2023

2023-09-17T10:42:29Z

Ross-spencer: Initial summary information about H2

2023-09-17T10:41:09Z

Initial summary information about H2

New page

{{FormatInfo
|subcat=Databases
|extensions={{ext|db}}
|mimetypes=
|pronom=
}}
'''h2database''' (H2) is an open source JAVA SQL database that can be used as an embedded, server, or in-memory database.

== Embedded format ==

H2's embedded format is a [https://www.h2database.com/html/mvstore.html#fileFormat MVStore file]. An example header is as follows:

<pre>
00000000: 48 3a 32 2c 62 6c 6f 63 6b 3a 33 2c 62 6c 6f 63 H:2,block:3,bloc
00000010: 6b 53 69 7a 65 3a 31 30 30 30 2c 63 68 75 6e 6b kSize:1000,chunk
00000020: 3a 37 2c 63 72 65 61 74 65 64 3a 31 38 61 39 66 :7,created:18a9f
00000030: 61 34 64 65 35 39 2c 66 6f 72 6d 61 74 3a 32 2c a4de59,format:2,
00000040: 76 65 72 73 69 6f 6e 3a 37 2c 66 6c 65 74 63 68 version:7,fletch
00000050: 65 72 3a 33 35 34 65 34 38 65 31 0a 00 00 00 00 er:354e48e1.....
</pre>

From the documentation:

<blockquote>
There are two file headers, which normally contain the exact same data. But once in a while, the file headers are updated, and writing could partially fail, which could corrupt a header. That's why there is a second header. Only the file headers are updated in this way (called "in-place update"). The headers contain the following data:
</blockquote>

<blockquote>
The data is stored in one file. The file contains two file headers (for safety), and a number of chunks. The file headers are one block each; a block is 4096 bytes.
</blockquote>

The fields are broken down in version 1 of the docs as follows:

* H: The entry "H:2" stands for the H2 database.
* block: The block number where one of the newest chunks starts (but not necessarily the newest).
* blockSize: The block size of the file; currently always hex 1000, which is decimal 4096, to match the * * disk sector length of modern hard disks.
* chunk: The chunk id, which is normally the same value as the version; however, the chunk id might roll over to 0, while the version doesn't.
* created: The number of milliseconds since 1970 when the file was created.
* format: The file format number. Currently 1.
* version: The version number of the chunk.
* fletcher: The Fletcher-32 checksum of the header.

<br>

=== Additional files in H2's persistent implementation ===

H2's database objects are described as follows. It may be important to identify these together in a preservation context but the documentation is unclear as to whether the database file can be interpreted in its own right.

{|

! File Name
! Description
! Number of Files

|-
| test.mv.db
| Database file. Contains the transaction log, indexes, and data for all tables. Format: <database>.mv.db
| 1 per database

|-
| test.newFile
| Temporary file for database compaction. Contains the new MVStore file. Format: <database>.newFile
| 0 or 1 per database

|-
| test.tempFile
| Temporary file for database compaction. Contains the temporary MVStore file. Format: <database>.tempFile
| 0 or 1 per database

|-
| test.lock.db
| Database lock file.
Automatically (re-)created while the database is in use. Format: <database>.lock.db
| 1 per database (only if in use)

|-
| test.trace.db
| Trace file (if the trace option is enabled). Contains trace information. Format: <database>.trace.db Renamed to<database>.trace.db.old if too big.
| 0 or 1 per database

|-
| test.123.temp.db
| Temporary file. Contains a temporary blob or a large result set. Format: <database>.<id>.temp.db
| 1 per object

|-

|}

<br>

== Use in digital preservation ==

Fedora 6.0's webapp is backed by a H2 database by default.

== Further information ==

* [https://h2database.com/html/main.html H2 database documentation]
* [https://github.com/fcrepo/fcrepo fcrepo]
* [https://wiki.lyrasis.org/display/FEDORA6x/Properties fcrepo database configuration]

[[category:File formats with extension .db]]
[[category:SQL]]

@@ Line 49: / Line 49: @@
 <blockquote>
 No, it doesn't. Historic version of H2 (1.4.200 and older) use format 1, H2 2.0.* and 2.1.* use format 2, H2 2.2.* uses format 3. You cannot read actual version of H2 from headers of MVStore files, MVStore doesn't preserve it, only H2 does.
-</quote>
+</blockquote>
 Format signature development therefore might be as granular as overall "version" but it won't map to specific software.

← Older revision		Revision as of 15:30, 17 September 2023
Line 42:		Line 42:

	<br>		<br>
		+
		+	=== Versioning ===
		+
		+	From the developer [https://github.com/h2database/h2database/issues/3892#issuecomment-1722484540], the versioning doesn't map 1:1 onto major releases. It maps as follows:
		+
		+	<blockquote>
		+	No, it doesn't. Historic version of H2 (1.4.200 and older) use format 1, H2 2.0.* and 2.1.* use format 2, H2 2.2.* uses format 3. You cannot read actual version of H2 from headers of MVStore files, MVStore doesn't preserve it, only H2 does.
		+	</quote>
		+
		+	Format signature development therefore might be as granular as overall "version" but it won't map to specific software.

	=== Additional files in H2's persistent implementation ===		=== Additional files in H2's persistent implementation ===

@@ Line 99: / Line 99: @@
 * [https://github.com/fcrepo/fcrepo fcrepo]
 * [https://wiki.lyrasis.org/display/FEDORA6x/Properties fcrepo database configuration]
+* [https://github.com/h2database/h2database/issues/3892 GitHub issue asking for more information about format mapping]
 [[category:File formats with extension .db]]
 [[category:SQL]]