Subscription Connections

Most database Connections use polling to regularly fetch data on a user specified timer. Alternatively you can create a subscription. This means the data source will push updates rather than polling. It can be more efficient for frequently updating data.

Currently to create a subscription you should:

1. Create a "Kdb Streaming" connection type.
2. Specify that connection as a source and set the query. e.g. .u.sub[`tblname;::]

Behind the scenes, for every unique subscription including query the server will:

1. Open a connection to the streaming data source.
2. Send the subscription query.
3. Await incoming data and forward results to the dashboard. For kdb the result format is expected to be (`.u.upd;`tableName;tableData).
4. Keep the connection open until the dashboard is closed.

Basic example kdb code to create a subscription:

// On the kdb process - define subscription function and timer. .u.sub:{[tblName;symList] bb::.z.w; tName::tblName;}; .z.ts:{neg[bb] (`.u.upd;`t;update tName:@[get;`tName;`noTname] from ([] t:3#.z.t; a:2 3 4; s:`pp`oo`ii))}; system "t 500"; // From the query box on the dashboard: .u.sub[`demoName;::]

Kdb+ Subscription Tutorial

b