PostgreSQL 12 High Availability Cookbook - Third Edition

Timeshard introspection

Remember how we mentioned that timeshard sequence fields are bit-packed 64-bit integers? Well, BDR includes functions that make it possible to unpack a value to obtain the information it contains.

Let's try this by using the following query to unpack the event_id field in the event_log table:

SELECT event_id,     bdr.extract_nodeid_from_timeshard(event_id) AS node_id,    bdr.extract_localseqid_from_timeshard(event_id) AS seq_val,    bdr.extract_timestamp_from_timeshard(event_id) AS stamp FROM event_log;

If we insert one or two more rows from each of our nodes, we should see something like this:

With this technique, we can actually ...