jackc/pglogrepl

Only receive one record one time?

zhanghaiyang9999 opened this issue · 2 comments

zhanghaiyang9999 commented

HI @jackc, does the following code just can receive one changed record each time?

rawMsg, err := t.conn.ReceiveMessage(ctx)

If so, is there some performance issues if the changes are frequently(see add lots of table records in a short time)? thanks!

diabloneo commented

The message sent through Postgres logical replication protocol by pgoutput plugin carries more than record data.

For logical replication related protocols, following documents describe the protocol:

  1. https://www.postgresql.org/docs/current/protocol-replication.html
  2. https://www.postgresql.org/docs/current/protocol-logicalrep-message-formats.html

If t.conn.ReceiveMessage() returns a CopyData message, it may contains record data represent as WAL data. Event if the data received is a XLogData, it may be something other the recorded being updated.

zhanghaiyang9999 commented

The message sent through Postgres logical replication protocol by pgoutput plugin carries more than record data.

For logical replication related protocols, following documents describe the protocol:

  1. https://www.postgresql.org/docs/current/protocol-replication.html
  2. https://www.postgresql.org/docs/current/protocol-logicalrep-message-formats.html

If t.conn.ReceiveMessage() returns a CopyData message, it may contains record data represent as WAL data. Event if the data received is a XLogData, it may be something other the recorded being updated.

Thanks @diabloneo ,From the example https://github.com/jackc/pglogrepl/blob/master/example/pglogrepl_demo/main.go
The example seems that only can handle one record(insert ,update or delete) every time, and for *pglogrepl.InsertMessage, the col.DataType has 3 cases, one is 'u', the others are 'n' and 't', I can understand the 'n' and 't' types for the insertMesage, but for 'u' , I don't know when will it happen. Thanks @diabloneo