The output of the EXPLAIN statement includes information about time zero when using VERBOSE EXPLAIN; for example:
...
We begin the time series aggregate calculation using
time zero <time_zero>
...
<time_zero> displays the type and constant value calculated as the time zero to use for a GROUP BY TIME query (such as, TIMESTAMP '2014-01-06 08:00:00.000000+00:00' ). This information appears in the SUM step of the EXPLAIN output.
Other information about time series queries can be deduced from the current EXPLAIN output:
- Information about which optimization plan for single threaded aggregate execution is in use
- Specification of each aggregate function as fully parallel or single threaded
- Specification of any sorting or redistribution performed prior to the aggregation (this is important for single threaded aggregate evaluation)
- Specification of any sorting or redistribution performed after the aggregation (this is important for FILL directive evaluation)
- Execution of FILL directive prints (fill empty groups in the time series with <value>).