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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/src/sgml/protocol.sgml | 26 |
1 files changed, 19 insertions, 7 deletions
diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml index b692648fca..84ddab0998 100644 --- a/doc/src/sgml/protocol.sgml +++ b/doc/src/sgml/protocol.sgml @@ -2891,13 +2891,25 @@ The commands accepted in replication mode are: </para> <para> - Every DML message contains an arbitrary relation ID, which can be mapped to - an ID in the Relation messages. The Relation messages describe the schema of the - given relation. The Relation message is sent for a given relation either - because it is the first time we send a DML message for given relation in the - current session or because the relation definition has changed since the - last Relation message was sent for it. The protocol assumes that the client - is capable of caching the metadata for as many relations as needed. + Every DML message contains a relation OID, identifying the publisher's + relation that was acted on. Before the first DML message for a given + relation OID, a Relation message will be sent, describing the schema of + that relation. Subsequently, a new Relation message will be sent if + the relation's definition has changed since the last Relation message + was sent for it. (The protocol assumes that the client is capable of + remembering this metadata for as many relations as needed.) + </para> + + <para> + Relation messages identify column types by their OIDs. In the case + of a built-in type, it is assumed that the client can look up that + type OID locally, so no additional data is needed. For a non-built-in + type OID, a Type message will be sent before the Relation message, + to provide the type name associated with that OID. Thus, a client that + needs to specifically identify the types of relation columns should + cache the contents of Type messages, and first consult that cache to + see if the type OID is defined there. If not, look up the type OID + locally. </para> </sect2> </sect1> |