dpif-netdev: Change polled_queue to use dp_netdev_rxq.

[ovs.git] / ovsdb / ovsdb-server.1.in

.\" -*- nroff -*-
.de IQ
.  br
.  ns
.  IP "\\$1"
..
.TH ovsdb\-server 1 "@VERSION@" "Open vSwitch" "Open vSwitch Manual"
.\" This program's name:
.ds PN ovsdb\-server
.
.SH NAME
ovsdb\-server \- Open vSwitch database server
.
.SH SYNOPSIS
\fBovsdb\-server\fR
[\fIdatabase\fR]\&...
[\fB\-\-remote=\fIremote\fR]\&...
[\fB\-\-run=\fIcommand\fR]
.so lib/daemon-syn.man
.so lib/service-syn.man
.so lib/vlog-syn.man
.so ovsdb/replication-syn.man
.so lib/ssl-syn.man
.so lib/ssl-bootstrap-syn.man
.so lib/ssl-peer-ca-cert-syn.man
.so lib/ssl-connect-syn.man
.so lib/unixctl-syn.man
.so lib/common-syn.man
.
.SH DESCRIPTION
The \fBovsdb\-server\fR program provides RPC interfaces to one or more
Open vSwitch databases (OVSDBs).  It supports JSON-RPC client
connections over active or passive TCP/IP or Unix domain sockets.
.PP
Each OVSDB file may be specified on the command line as \fIdatabase\fR.
If none is specified, the default is \fB@DBDIR@/conf.db\fR.  The database
files must already have been created and initialized using, for
example, \fBovsdb\-tool create\fR.
.
.SH "ACTIVE and BACKUP"
\fBovsdb\-server\fR runs either as a backup server, or as an active server.
When  \fBovsdb\-server\fR is running as a backup server, all transactions that
can modify the database content, including the lock commands are rejected.
Active server, on the other hand, accepts all ovsdb server transactions.
When \fBovsdb\-server\fR role changes, all existing client connection are
reset, requiring clients to reconnect to the server.
.PP
By default, \fBovsdb\-server\fR runs as an active server, except when the
\fB\-\-sync\-from=\fIserver\fR command line option is specified and without
the \fB\-\-no\-sync option\fR.  During runtime, \fBovsdb\-server\fR role can be switch by using appctl commands.
.PP
\fBovsdb-server/connect\-active\-ovsdb\-server\fR switches
\fBovsdb\-server\fR into a backup server, Conversely,
\fBovsdb-server/disconnect\-active\-ovsdb\-server\fR switches server into
an active one.
.
.SH OPTIONS
.
.IP "\fB\-\-remote=\fIremote\fR"
Adds \fIremote\fR as a connection method used by \fBovsdb\-server\fR.
\fIremote\fR must take one of the following forms:
.
.RS
.so ovsdb/remote-passive.man
.so ovsdb/remote-active.man
.
.IP "\fBdb:\fIdb\fB,\fItable\fB,\fIcolumn\fR"
Reads additional connection methods from \fIcolumn\fR in all of the
rows in \fItable\fR within \fIdb\fR.  As the contents of \fIcolumn\fR changes,
\fBovsdb\-server\fR also adds and drops connection methods accordingly.
.IP
If \fIcolumn\fR's type is string or set of strings, then the
connection methods are taken directly from the column.  The connection
methods in the column must have one of the forms described above.
.IP
If \fIcolumn\fR's type is UUID or set of UUIDs and references a table,
then each UUID is looked up in the referenced table to obtain a row.
The following columns in the row, if present and of the correct type,
configure a connection method.  Any additional columns are ignored.
.RS
.IP "\fBtarget\fR (string)"
Connection method, in one of the forms described above.  This column
is mandatory: if it is missing or empty then no connection method can
be configured.
.IP "\fBmax_backoff\fR (integer)"
Maximum number of milliseconds to wait between connection attempts.
.IP "\fBinactivity_probe\fR (integer)"
Maximum number of milliseconds of idle time on connection to
client before sending an inactivity probe message.
.IP "\fBread_only\fR (boolean)"
If true, only read-only transactions are allowed on this connection.
.RE
.IP
It is an error for \fIcolumn\fR to have another type.
.RE
.
.IP
To connect or listen on multiple connection methods, use multiple
\fB\-\-remote\fR options.
.
.IP "\fB\-\-run=\fIcommand\fR]"
Ordinarily \fBovsdb\-server\fR runs forever, or until it is told to
exit (see \fBRUNTIME MANAGEMENT COMMANDS\fR below).  With this option,
\fBovsdb\-server\fR instead starts a shell subprocess running
\fIcommand\fR.  When the subprocess terminates, \fBovsdb\-server\fR
also exits gracefully.  If the subprocess exits normally with exit
code 0, then \fBovsdb\-server\fR exits with exit code 0 also;
otherwise, it exits with exit code 1.
.IP
This option can be useful where a database server is needed only to
run a single command, e.g.:
.B "ovsdb\-server \-\-remote=punix:socket \-\-run='ovsdb\-client dump unix:socket Open_vSwitch'"
.IP
This option is not supported on Windows platform.
.SS "Daemon Options"
.ds DD \
\fBovsdb\-server\fR detaches only after it starts listening on all \
configured remotes.
.so lib/daemon.man
.SS "Service Options"
.so lib/service.man
.SS "Logging Options"
.so lib/vlog.man
.SS "Syncing Options"
.so ovsdb/replication.man
.SS "Public Key Infrastructure Options"
The options described below for configuring the SSL public key
infrastructure accept a special syntax for obtaining their
configuration from the database.  If any of these options is given
\fBdb:\fIdb\fB,\fItable\fB,\fIcolumn\fR as its argument, then the
actual file name is read from the specified \fIcolumn\fR in \fItable\fR
within the \fIdb\fR database.  The \fIcolumn\fR must have type
string or set of strings.  The first nonempty string in the table is taken
as the file name.  (This means that ordinarily there should be at most
one row in \fItable\fR.)
.so lib/ssl.man
.so lib/ssl-bootstrap.man
.so lib/ssl-peer-ca-cert.man
.SS "SSL Connection Options"
.so lib/ssl-connect.man
.SS "Other Options"
.so lib/unixctl.man
.so lib/common.man
.SH "RUNTIME MANAGEMENT COMMANDS"
\fBovs\-appctl\fR(8) can send commands to a running
\fBovsdb\-server\fR process.  The currently supported commands are
described below.
.SS "OVSDB\-SERVER COMMANDS"
These commands are specific to \fBovsdb\-server\fR.
.IP "\fBexit\fR"
Causes \fBovsdb\-server\fR to gracefully terminate.
.IP "\fBovsdb\-server/compact\fR [\fIdb\fR]\&..."
Compacts each database \fIdb\fR in-place.  If no \fIdb\fR is
specified, compacts every database in-place.  A database is also
compacted automatically when a transaction is logged if it is over 4
times as large as its previous compacted size (and at least 10 MB),
but not before 100 commits have been added or 10 minutes have elapsed
since the last compaction.
.
.IP "\fBovsdb\-server/reconnect\fR"
Makes \fBovsdb\-server\fR drop all of the JSON\-RPC
connections to database clients and reconnect.
.IP
This command might be useful for debugging issues with database
clients.
.
.IP "\fBovsdb\-server/add\-remote \fIremote\fR"
Adds a remote, as if \fB\-\-remote=\fIremote\fR had been specified on
the \fBovsdb\-server\fR command line.  (If \fIremote\fR is already a
remote, this command succeeds without changing the configuration.)
.
.IP "\fBovsdb\-server/remove\-remote \fIremote\fR"
Removes the specified \fIremote\fR from the configuration, failing
with an error if \fIremote\fR is not configured as a remote.  This
command only works with remotes that were named on \fB\-\-remote\fR or
\fBovsdb\-server/add\-remote\fR, that is, it will not remove remotes
added indirectly because they were read from the database by
configuring a \fBdb:\fIdb\fB,\fItable\fB,\fIcolumn\fR remote.
(You can remove a database source with \fBovsdb\-server/remove\-remote
\fBdb:\fIdb\fB,\fItable\fB,\fIcolumn\fR, but not individual
remotes found indirectly through the database.)
.
.IP "\fBovsdb\-server/list\-remotes"
Outputs a list of the currently configured remotes named on
\fB\-\-remote\fR or \fBovsdb\-server/add\-remote\fR, that is, it does
not list remotes added indirectly because they were read from the
database by configuring a
\fBdb:\fIdb\fB,\fItable\fB,\fIcolumn\fR remote.
.
.IP "\fBovsdb\-server/add\-db \fIdatabase\fR"
Adds the \fIdatabase\fR to the running \fBovsdb\-server\fR.  The database
file must already have been created and initialized using, for example,
\fBovsdb\-tool create\fR.
.
.IP "\fBovsdb\-server/remove\-db \fIdatabase\fR"
Removes \fIdatabase\fR from the running \fBovsdb\-server\fR.  \fIdatabase\fR
must be a database name as listed by \fBovsdb-server/list\-dbs\fR.
.IP
If a remote has been configured that points to the specified
\fIdatabase\fR (e.g. \fB\-\-remote=db:\fIdatabase\fB,\fR... on the
command line), then it will be disabled until another database with
the same name is added again (with \fBovsdb\-server/add\-db\fR).
.IP
Any public key infrastructure options specified through this database
(e.g. \fB\-\-private\-key=db:\fIdatabase,\fR... on the command line)
will be disabled until another database with the same name is added
again (with \fBovsdb\-server/add\-db\fR).
.
.IP "\fBovsdb\-server/list\-dbs"
Outputs a list of the currently configured databases added either through
the command line or through the \fBovsdb\-server/add\-db\fR command.
.
.IP "\fBovsdb\-server/set\-active\-ovsdb\-server \fIserver"
Sets  the active \fIserver\fR from which \fBovsdb\-server\fR connects through
\fBovsdb\-server/connect\-active\-ovsdb\-server\fR.
.
.IP "\fBovsdb\-server/get\-active\-ovsdb\-server"
Gets the active server from which \fBovsdb\-server\fR is currently synchronizing
its databases.
.
.IP "\fBovsdb\-server/connect\-active\-ovsdb\-server"
Causes \fBovsdb\-server\fR to synchronize its databases with the server
specified by \fBovsdb\-server/set\-active\-ovsdb\-server\fR.
.
.IP "\fBovsdb\-server/disconnect\-active\-ovsdb\-server"
Causes \fBovsdb\-server\fR to  stop  synchronizing  its  databases with a active server.
.
.IP "\fBovsdb\-server/set\-sync\-exclude\-tables \fIdb\fB:\fItable\fR[\fB,\fIdb\fB:\fItable\fR]..."
Sets the \fItable\fR whitin \fIdb\fR that will be excluded from synchronization.
.
.IP "\fBovsdb\-server/get\-sync\-exclude\-tables"
Gets  the  tables  that are currently excluded from synchronization.
.
.IP "\fBovsdb\-server/sync\-status"
Prints a summary of replication run time information. The \fBstate\fR
information is always provided, indicating whether the server is running
in the \fIactive\fR or the \fIbackup\fR mode.
When running in backup mode, replication connection status, which
can be either \fIconnecting\fR, \fIreplicating\fR or \fIerror\fR, are shown.
When the connection is in \fIreplicating\fR state, further output shows
the list of databases currently replicating, and the tables that are
excluded.
.
.so lib/vlog-unixctl.man
.so lib/memory-unixctl.man
.so lib/coverage-unixctl.man
.SH "SPECIFICATIONS"
.
.PP
\fBovsdb\-server\fR implements the Open vSwitch Database (OVSDB)
protocol specified in RFC 7047, with the following clarifications:
.
.IP "3.1. JSON Usage"
RFC 4627 says that names within a JSON object should be unique.
The Open vSwitch JSON parser discards all but the last value
for a name that is specified more than once.
.
.IP
The definition of <error> allows for implementation extensions.
Currently \fBovsdb\-server\fR uses the following additional "error"
strings which might change in later releases):
.
.RS
.IP "\fBsyntax error\fR or \fBunknown column\fR"
The request could not be parsed as an OVSDB request.  An additional
"syntax" member, whose value is a string that contains JSON, may
narrow down the particular syntax that could not be parsed.
.IP "\fBinternal error\fR"
The request triggered a bug in \fBovsdb\-server\fR.
.IP "\fBovsdb error\fR"
A map or set contains a duplicate key.
.IP "\fBpermission error\fR"
The request was denied by the role-based access control extension,
introduced in version 2.8.
.RE
.
.IP "3.2. Schema Format"
RFC 7047 requires the "version" field in <database-schema>.  Current
versions of \fBovsdb\-server\fR allow it to be omitted (future
versions are likely to require it).
.IP
RFC 7047 allows columns that contain weak references to be immutable.
This raises the issue of the behavior of the weak reference when the
rows that it references are deleted.  Since version 2.6,
\fBovsdb\-server\fR forces columns that contain weak references to be
mutable.
.IP
Since version 2.8, the table name \fBRBAC_Role\fR is used internally
by the role-based access control extension to \fBovsdb\-server\fR and
should not be used for purposes other than defining mappings of role
names to table access permissions. This table has one row per role
name and the following columns:
.RS
.IP "\fBname\fR"
The role name.
.IP "\fBpermissions\fR"
A map of table name to a reference to a row in a separate permission
table.
.RE
.IP
The separate RBAC permission table has one row per access control
configuration and the following columns:
.RS
.IP "\fBname\fR"
The name of the table to which the row applies.
.IP "\fBauthorization\fR"
The set of column names and column:key pairs to be compared with
the client ID in order to determine the authorization status of
the requested operation.
.IP "\fBinsert_delete\fR"
A boolean value, true if authorized insertions and authorized are allowed,
false if no insertions or deletions are allowed.
.IP "\fBupdate\fR"
The set of columns and column:key pairs for which authorized update and
mutate operations should be permitted.
.RE
.
.IP "4. Wire Protocol"
The original OVSDB specifications included the following reason,
omitted from RFC 7047, to operate JSON-RPC directly over a stream
instead of over HTTP:
.
.RS
.IP \(bu
JSON-RPC is a peer-to-peer protocol, but HTTP is a client-server
protocol, which is a poor match.  Thus, JSON-RPC over HTTP requires
the client to periodically poll the server to receive server requests.
.IP \(bu
HTTP is more complicated than stream connections and doesn't provide
any corresponding advantage.
.IP \(bu
The JSON-RPC specification for HTTP transport is incomplete.
.RE
.
.IP "4.1.3. Transact"
Since version 2.8, role-based access controls can be applied to operations
within a transaction that would modify the contents of the database
(these operations include row insert, row delete, column update, and
column mutate). Role-based access controls are applied when the database
schema contains a table with the name "\fBRBAC_Role\fR" and the connection
on which the transaction request was received has an associated role
name (from the "\fBrole\fR" column in the remote connection table). When
role-based access controls are enabled, transactions that are otherwise
well-formed may be rejected depending on the client's role, ID, and the
contents of the \fBRBAC_Role\fR table and associated permissions table.
.
.IP "4.1.5. Monitor"
For backward compatibility, \fBovsdb\-server\fR currently permits a
single <monitor-request> to be used instead of an array; it is treated
as a single-element array.  Future versions of \fBovsdb\-server\fR
might remove this compatibility feature.
.IP
Because the <json-value> parameter is used to match subsequent update
notifications (see below) to the request, it must be unique among all
active monitors.  \fBovsdb\-server\fR rejects attempt to create two
monitors with the same identifier.
.
.IP "4.1.12. Monitor_cond"
A new monitor method added in Open vSwitch version 2.6. The monitor_cond
request enables a client to replicate subsets of tables within an OVSDB
database by requesting notifications of changes to rows matching one of
the conditions specified in "where" by receiving the specified contents
of these rows when table updates occur. Monitor_cond also allows a more
efficient update notifications by receiving table-updates2 notifications
(described below).
.
.IP
The monitor method described in Section 4.1.5 also applies to monitor_cond,
with the following exceptions:
.
.RS
.IP \(bu
RPC request method becomes "monitor_cond".
.IP \(bu
Reply result follows <table-updates2>, described in Section 4.1.14.
.IP \(bu
Subsequent changes are sent to the client using the "update2" monitor
notification, described in Section 4.1.14
.IP \(bu
Update notifications are being sent only for rows matching [<condition>*].
.RE
.
.IP
The request object has the following members:
.
.PP
.RS
.nf
"method": "monitor_cond"
"params": [<db-name>, <json-value>, <monitor-cond-requests>]
"id": <nonnull-json-value>
.fi
.RE
.
.IP
The <json-value> parameter is used to match subsequent update notifications
(see below) to this request. The <monitor-cond-requests> object maps the name
of the table to an array of <monitor-cond-request>.
.
.IP
Each <monitor-cond-request> is an object with the following members:
.
.PP
.RS
.nf
"columns": [<column>*]            optional
"where": [<condition>*]           optional
"select": <monitor-select>        optional
.fi
.RE
.
.IP
The "columns", if present, define the columns within the table to be monitored
that match conditions. If not present all columns are being monitored.
.
.IP
The "where" if present is a JSON array of <condition> and boolean values. If not
present or condition is an empty array, implicit True will be considered and
updates on all rows will be sent.
.
.IP
<monitor-select> is an object with the following members:
.
.PP
.RS
.nf
"initial": <boolean>              optional
"insert": <boolean>               optional
"delete": <boolean>               optional
"modify": <boolean>               optional
.fi
.RE
.
.IP
The contents of this object specify how the columns or table are to be
monitored as explained in more detail below.
.
.IP
The response object has the following members:
.
.PP
.RS
.nf
"result": <table-updates2>
"error": null
"id": same "id" as request
.fi
.RE
.
.IP
The <table-updates2> object is described in detail in Section 4.1.14. It
contains the contents of the tables for which "initial" rows are selected.
If no tables initial contents are requested, then "result" is an empty object.
.
.IP
Subsequently, when changes to a specified table that match one of the conditions
in monitor-cond-request are committed, the changes are automatically sent to the
client using the "update2" monitor notification (see Section 4.1.14). This
monitoring persists until the JSON-RPC session terminates or until the client
sends a "monitor_cancel" JSON-RPC request.
.
.IP
Each <monitor-cond-request> specifies one or more conditions and the manner in
which the rows that match the conditions are to be monitored. The circumstances in
which an "update" notification is sent for a row within the table are determined by
<monitor-select>:
.
.RS
.IP \(bu
If "initial" is omitted or true, every row in the original table that matches one of
the conditions is sent as part of the response to the "monitor_cond" request.
.IP \(bu
If "insert" is omitted or true, "update" notifications are sent for rows newly
inserted into the table that match conditions or for rows modified in the table
so that their old version does not match the condition and new version does.
.IP \(bu
If "delete" is omitted or true, "update" notifications are sent for rows deleted
from the table that match conditions or for rows modified in the table so that
their old version does match the conditions and new version does not.
.IP \(bu
If "modify" is omitted or true, "update" notifications are sent whenever a row in
the table that matches conditions in both old and new version is modified.
.RE
.
.IP
Both monitor and monitor_cond sessions can exist concurrently. However,
monitor and monitor_cond shares the same <json-value> parameter space; it
must be unique among all monitor and monitor_cond sessions.
.
.IP "4.1.13. Monitor_cond_change"
The "monitor_cond_change" request enables a client to change an existing
"monitor_cond" replication of the database by specifying a new condition
and columns for each replicated table. Currently changing the columns set
is not supported.
.
.IP
The request object has the following members:
.
.IP
.RS
.nf
"method": "monitor_cond_change"
"params": [<json-value>, <json-value>, <monitor-cond-update-requests>]
"id": <nonnull-json-value>
.fi
.RE
.
.IP
The <json-value> parameter should have a value of an existing conditional
monitoring session from this client. The second <json-value> in params array
is the requested value for this session. This value is valid only after
"monitor_cond_change" is committed. A user can use these values to distinguish
between update messages before conditions update and after. The
<monitor-cond-update-requests> object maps the name of the table to an array of
<monitor-cond-update-request>.
.
.IP
Each <monitor-cond-update-request> is an object with the following members:
.
.IP
.RS
.nf
"columns": [<column>*]         optional
"where": [<condition>*]        optional
.fi
.RE
.
.IP
The "columns" specify a new array of columns to be monitored
(Currently unsupported).
.
.IP
The "where" specify a new array of conditions to be applied to this monitoring
session.
.
.IP
The response object has the following members:
.
.IP
.RS
.nf
"result": null
"error": null
"id": same "id" as request
.fi
.RE
.IP
Subsequent <table-updates2> notifications are described in detail in Section
4.1.14 in the RFC. If insert contents are requested by original monitor_cond
request, <table-updates2> will contain rows that match the new condition and
do not match the old condition.
If deleted contents are requested by origin monitor request, <table-updates2>
will contain any matched rows by old condition and not matched by the new
condition.
.
.IP
Changes according to the new conditions are automatically sent to the client
using the "update2" monitor notification. An update, if any, as a result of a
condition change, will be sent to the client before the reply to the
"monitor_cond_change" request.
.
.IP "4.1.14. Update2 notification"
The "update2" notification is sent by the server to the client to report
changes in tables that are being monitored following a "monitor_cond" request
as described above. The notification has the following members:
.
.RS
.nf
"method": "update2"
"params": [<json-value>, <table-updates2>]
"id": null
.fi
.RE
.
.IP
The <json-value> in "params" is the same as the value passed as the
<json-value>  in "params" for the corresponding "monitor" request.
<table-updates2> is an object that maps from a table name to a <table-update2>.
A <table-update2> is an object that maps from row's UUID to a <row-update2>
object. A <row-update2> is an object with one of the following members:
.
.RS
.IP "\(dqinitial\(dq: <row>"
present for "initial" updates
.IP "\(dqinsert\(dq: <row>"
present for "insert" updates
.IP "\(dqdelete\(dq: <row>"
present for "delete" updates
.IP "\(dqmodify\(dq: <row>"
present for "modify" updates
.RE
.
.IP
The format of <row> is described in Section 5.1.
.
.IP
<row> is always a null object for a "delete" update. In "initial" and
"insert" updates, <row> omits columns whose values equal the default
value of the column type.
.
.IP
For a "modify" update, <row> contains only the columns that are modified.
<row> stores the difference between the old and new value for those columns,
as described below.
.
.IP
For columns with single value, the difference is the value of the new
column.
.
.IP
The difference between two sets are all elements that only belong
to one of the sets.
.
.IP
The difference between two maps are all key-value pairs whose keys
appears in only one of the maps, plus the key-value pairs whose keys
appear in both maps but with different values.  For the latter
elements, <row> includes the value from the new column.
.
.IP
Initial views of rows are not presented in update2 notifications,
but in the response object to the monitor_cond request. The formatting
of the <table-updates2> object, however, is the same in either case.
.
.IP "4.1.15. Get Server ID"
A new RPC method added in Open vSwitch version 2.7. The request contains
the following members:
.
.PP
.RS
.nf
"method": "get_server_id"
"params": null
"id": <nonnull-json-value>
.fi
.RE
.
.IP
The response object contains the following members:
.
.PP
.RS
.nf
"result": "<server_id>"
"error": null
"id": same "id" as request
.fi
.RE
.
.IP
<server_id> is JSON string that contains a UUID that uniquely identifies
the running OVSDB server process. A fresh UUID is generated when the
process restarts.
.
.IP "5.1. Notation"
For <condition>, RFC 7047 only allows the use of \fB!=\fR, \fB==\fR,
\fBincludes\fR, and \fBexcludes\fR operators with set types.  Open
vSwitch 2.4 and later extend <condition> to allow the use of \fB<\fR,
\fB<=\fR, \fB>=\fR, and \fB>\fR operators with columns with type ``set
of 0 or 1 integer'' and ``set of 0 or 1 real''.  These conditions
evaluate to false when the column is empty, and otherwise as described
in RFC 7047 for integer and real types.
.
.IP
<condition> is specified in Section 5.1 in the RFC with the following change:
A condition can be either a 3-element JSON array as described in the RFC or a
boolean value. In case of an empty array an implicit true boolean value will be
considered.
.
.IP "5.2.6. Wait"
.IQ "5.2.7. Commit"
.IQ "5.2.9. Comment"
RFC 7047 says that the \fBwait\fR, \fBcommit\fR, and \fBcomment\fR
operations have no corresponding result object.  This is not true.
Instead, when such an operation is successful, it yields a result
object with no members.
.
.SH "BUGS"
.
In Open vSwitch before version 2.4, when \fBovsdb\-server\fR sent
JSON-RPC error responses to some requests, it incorrectly formulated
them with the \fBresult\fR and \fBerror\fR swapped, so that the
response appeared to indicate success (with a nonsensical result)
rather than an error.  The requests that suffered from this problem
were:
.
.IP \fBtransact\fR
.IQ \fBget_schema\fR
Only if the request names a nonexistent database.
.IP \fBmonitor\fR
.IQ \fBlock\fR
.IQ \fBunlock\fR
In all error cases.
.
.PP
Of these cases, the only error that a well-written application is
likely to encounter in practice is \fBmonitor\fR of tables or columns
that do not exist, in an situation where the application has been
upgraded but the old database schema is still temporarily in use.  To
handle this situation gracefully, we recommend that clients should
treat a \fBmonitor\fR response with a \fBresult\fR that contains an
\fBerror\fR key-value pair as an error (assuming that the database
being monitored does not contain a table named \fBerror\fR).
.
.SH "SEE ALSO"
.
.BR ovsdb\-tool (1).