ovsdb man page
ovsdb — Open vSwitch Database (File Formats)
OVSDB, the Open vSwitch Database, is a database system whose network protocol is specified by RFC 7047. The RFC does not specify an on-disk storage format. This manpage documents the format used by Open vSwitch.
Most users do not need to be concerned with this specification. Instead, to manipulate OVSDB files, refer to ovsdb-tool(1). For an introduction to OVSDB as a whole, read ovsdb(7).
OVSDB files explicitly record changes that are implied by the database schema. For example, the OVSDB “garbage collection” feature means that when a client removes the last reference to a garbage-collected row, the database server automatically removes that row. The database file explicitly records the deletion of the garbage-collected row, so that the reader does not need to infer it.
OVSDB files do not include the values of ephemeral columns.
Database files are text files encoded in UTF-8 with LF (U+000A) line ends, organized as append-only series of records. Each record consists of 2 lines of text.
The first line in each record has the format OVSDB JSON length hash, where length is a positive decimal integer and hash is a SHA-1 checksum expressed as 40 hexadecimal digits. Words in the first line must be separated by exactly one space.
The second line must be exactly length bytes long (including the LF) and its SHA-1 checksum (including the LF) must match hash exactly. The line’s contents must be a valid JSON object as specified by RFC 4627. Strings in the JSON object must be valid UTF-8. To ensure that the second line is exactly one line of text, the OVSDB implementation expresses any LF characters within a JSON string as \n. For the same reason, and to save space, the OVSDB implementation does not “pretty print” the JSON object with spaces and LFs. (The OVSDB implementation tolerates LFs when reading an OVSDB database file, as long as length and hash are correct.)
We use notation from RFC 7047 here to describe the JSON data in records. In addition to the notation defined there, we add the following:
A 36-character JSON string that contains a UUID in the format described by RFC 4122, e.g. "550e8400-e29b-41d4-a716-446655440000"
The first record in a standalone database contains the JSON schema for the database, as specified in RFC 7047. Only this record is mandatory (a standalone file that contains only a schema represents an empty database).
The second and subsequent records in a standalone database are transaction records. Each record may have the following optional special members, which do not have any semantics but are often useful to administrators looking through a database log with ovsdb-tool show-log:
- "_date": <integer>
The time at which the transaction was committed, as an integer number of milliseconds since the Unix epoch. Early versions of OVSDB counted seconds instead of milliseconds; these can be detected by noticing that their values are less than 2**32.
OVSDB always writes a _date member.
- "_comment": <string>
A JSON string that specifies the comment provided in a transaction comment operation. If a transaction has multiple comment operations, OVSDB concatenates them into a single _comment member, separated by a new-line.
OVSDB only writes a _comment member if it would be a nonempty string.
Each of these records also has one or more additional members, each of which maps from the name of a database table to a <table-txn>:
A JSON object that describes the effects of a transaction on a database table. Its names are <raw-uuid>s for rows in the table and its values are <row-txn>s.
Either null, which indicates that the transaction deleted this row, or a JSON object that describes how the transaction inserted or modified the row, whose names are the names of columns and whose values are <value>s that give the column’s new value.
For new rows, the OVSDB implementation omits columns whose values have the default values for their types defined in RFC 7047 section 5.2.1; for modified rows, the OVSDB implementation omits columns whose values are unchanged.
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