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NAME | DESCRIPTION | AUTHOR | COPYRIGHT | COLOPHON |
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OVSDB(5) Open vSwitch OVSDB(5)
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. The OVSDB implementation in
Open vSwitch implements two storage formats: one for standalone
(and active-backup) databases, and the other for clustered
databases. This manpage documents both of these formats.
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.
Standalone and clustered database files share the common
structure described here. They 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 <magic>
<length> <hash>, where <magic> is JSON for standalone databases
or CLUSTER for clustered databases, <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.)
JSON Notation
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:
<raw-uuid>
A 36-character JSON string that contains a UUID in the
format described by RFC 4122, e.g.
"550e8400-e29b-41d4-a716-446655440000"
Standalone Format
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>:
<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.
<row-txn>
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.
Clustered Format
The clustered format has the following additional notation:
<uint64>
A JSON integer that represents a 64-bit unsigned integer.
The OVS JSON implementation only supports integers in the
range -2**63 through 2**63-1, so 64-bit unsigned integer
values from 2**63 through 2**64-1 are expressed as
negative numbers.
<address>
A JSON string that represents a network address to support
clustering, in the <protocol>:<ip>:<port> syntax described
in ovsdb-tool(1).
<servers>
A JSON object whose names are <raw-uuid>s that identify
servers and whose values are <address>es that specify
those servers’ addresses.
<cluster-txn>
A JSON array with two elements:
1. The first element is either a <database-schema> or
null. A <database-schema> element is always present in
the first record of a clustered database to indicate
the database’s initial schema. If it is not null in a
later record, it indicates a change of schema for the
database.
2. The second element is either a transaction record in
the format described under Standalone Format above, or
null.
When a schema is present, the transaction record is
relative to an empty database. That is, a schema change
effectively resets the database to empty and the
transaction record represents the full database contents.
This allows readers to be ignorant of the full semantics
of schema change.
The first record in a clustered database contains the following
members, all of which are required, except prev_election_timer:
"server_id": <raw-uuid>
The server’s own UUID, which must be unique within the
cluster.
"local_address": <address>
The address on which the server listens for connections
from other servers in the cluster.
"name": <id>
The database schema name. It is only important when a
server is in the process of joining a cluster: a server
will only join a cluster if the name matches. (If the
database schema name were unique, then we would not also
need a cluster ID.)
"cluster_id": <raw-uuid>
The cluster’s UUID. The all-zeros UUID is not a valid
cluster ID.
"prev_term": <uint64> and "prev_index": <uint64>
The Raft term and index just before the beginning of the
log.
"prev_servers": <servers>
The set of one or more servers in the cluster at index
“prev_index” and term “prev_term”. It might not include
this server, if it was not the initial server in the
cluster.
"prev_election_timer": <uint64>
The election base time before the beginning of the log.
If not exist, the default value 1000 ms is used as if it
exists this record.
"prev_data": <json-value> and "prev_eid": <raw-uuid>
A snapshot of the data in the database at index
“prev_index” and term “prev_term”, and the entry ID for
that data. The snapshot must contain a schema.
The second and subsequent records, if present, in a clustered
database represent changes to the database, to the cluster state,
or both. There are several types of these records. The most
important types of records directly represent persistent state
described in the Raft specification:
Entry A Raft log entry.
Term The start of a new term.
Vote The server’s vote for a leader in the current term.
The following additional types of records aid debugging and
troubleshooting, but they do not affect correctness.
Leader Identifies a newly elected leader for the current term.
Commit Index
An update to the server’s commit_index.
Note A human-readable description of some event.
The table below identifies the members that each type of record
contains. “yes” indicates that a member is required, “?” that it
is optional, blank that it is forbidden, and [1] that data and
eid must be either both present or both absent.
┌────────────────┬───────┬──────┬──────┬────────┬────────┬──────┐
│ member │ Entry │ Term │ Vote │ Leader │ Commit │ Note │
│ │ │ │ │ │ Index │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ comment │ ? │ ? │ ? │ ? │ ? │ ? │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ term │ yes │ yes │ yes │ yes │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ index │ yes │ │ │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ servers │ ? │ │ │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ election_timer │ ? │ │ │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ data │ [1] │ │ │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ eid │ [1] │ │ │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ vote │ │ │ yes │ │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ leader │ │ │ │ yes │ │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ commit_index │ │ │ │ │ yes │ │
├────────────────┼───────┼──────┼──────┼────────┼────────┼──────┤
│ note │ │ │ │ │ │ yes │
└────────────────┴───────┴──────┴──────┴────────┴────────┴──────┘
The members are:
"comment": <string>
A human-readable string giving an administrator more
information about the reason a record was emitted.
"term": <uint64>
The term in which the activity occurred.
"index": <uint64>
The index of a log entry.
"servers": <servers>
Server configuration in a log entry.
"election_timer": <uint64>
Leader election timeout base value in a log entry.
"data": <json-value>
The data in a log entry.
"eid": <raw-uuid>
Entry ID in a log entry.
"vote": <raw-uuid>
The server ID for which this server voted.
"leader": <raw-uuid>
The server ID of the server. Emitted by both leaders and
followers when a leader is elected.
"commit_index": <uint64>
Updated commit_index value.
"note": <string>
One of a few special strings indicating important events.
The currently defined strings are:
"transfer leadership"
This server transferred leadership to a different
server (with details included in comment).
"left" This server finished leaving the cluster. (This
lets subsequent readers know that the server is not
part of the cluster and should not attempt to
connect to it.)
Joining a Cluster
In addition to general format for a clustered database, there is
also a special case for a database file created by ovsdb-tool
join-cluster. Such a file contains exactly one record, which
conveys the information passed to the join-cluster command. It
has the following members:
"server_id": <raw-uuid> and "local_address": <address> and
"name": <id>
These have the same semantics described above in the
general description of the format.
"cluster_id": <raw-uuid>
This is provided only if the user gave the --cid option to
join-cluster. It has the same semantics described above.
"remote_addresses"; [<address>*]
One or more remote servers to contact for joining the
cluster.
When the server successfully joins the cluster, the database file
is replaced by one described in Clustered Format.
The Open vSwitch Development Community
2016-2021, The Open vSwitch Development Community
This page is part of the Open vSwitch (a distributed virtual
multilayer switch) project. Information about the project can be
found at ⟨http://openvswitch.org/⟩. If you have a bug report for
this manual page, send it to bugs@openvswitch.org. This page was
obtained from the project's upstream Git repository
⟨https://github.com/openvswitch/ovs.git⟩ on 2023-12-22. (At that
time, the date of the most recent commit that was found in the
repository was 2023-12-21.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
3.2.90 Dec 22, 2023 OVSDB(5)
Pages that refer to this page: ovsdb-tool(1), ovsdb(7)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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