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.   In‐
       stead,  to  manipulate OVSDB files, refer to ovsdb-tool(1).  For an in‐
       troduction 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 de‐
       scribed 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  ex‐
       presses  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 follow‐

              A  36-character  JSON  string that contains a UUID in the format
              described          by          RFC          4122,           e.g.

   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

       The second and subsequent records in a standalone database are transac‐
       tion records.  Each record may have the following optional special mem‐
       bers, which do not have any semantics but are often useful to  adminis‐
       trators 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 de‐
              tected 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  transac‐
              tion  comment  operation.  If a transaction has multiple comment
              operations, OVSDB concatenates them into a single _comment  mem‐
              ber, separated by a new-line.

              OVSDB  only  writes  a _comment member if it would be a nonempty

       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  in‐
              serted 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  val‐
              ues  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:

              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.

              A JSON string that represents a network address to support clus‐
              tering,   in  the  <protocol>:<ip>:<port>  syntax  described  in

              A JSON object whose names are <raw-uuid>s that identify  servers
              and whose values are <address>es that specify those servers’ ad‐

              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 in‐
                 dicates a change of schema for the database.

              2. The second element is either a transaction record in the for‐
                 mat 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 mem‐
       bers, 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

       "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_in‐
              dex” 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

       "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 spec‐

       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 trou‐
       bleshooting, 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  con‐
       tains.   “yes”  indicates that a member is required, “?” that it is op‐
       tional, 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 In‐ │ Note │
           │           │       │      │      │        │ dex        │      │
           │comment    │ ?     │ ?    │ ?    │ ?      │ ?          │ ?    │
           │term       │ yes   │ yes  │ yes  │ yes    │            │      │
           │index      │ yes   │      │      │        │            │      │
           │servers    │ ?     │      │      │        │            │      │
           │elec‐      │ ?     │      │      │        │            │      │
           │tion_timer │       │      │      │        │            │      │
           │data       │ [1]   │      │      │        │            │      │
           │eid        │ [1]   │      │      │        │            │      │
           │vote       │       │      │ yes  │        │            │      │
           │leader     │       │      │      │ yes    │            │      │
           │commit_in‐ │       │      │      │        │ yes        │      │
           │dex        │       │      │      │        │            │      │
           │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 fol‐
              lowers 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 de‐
              scription 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.

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3.3                              Feb 17, 2024                         OVSDB(5)