How to Efficiently Truncate Timestamps to 5-Minute Intervals in PostgreSQL?

Efficiently Truncating Timestamps to 5-Minute Intervals in PostgreSQL

Truncating timestamps to a specific boundary is a frequent operation in database processing. For Postgres, the date_trunc function provides a straightforward way to round timestamps to the hour or minute. However, truncating to the nearest 5-minute interval requires a more customized approach.

The Straightforward Approach

The typical solution for 5-minute truncation is to combine date_trunc with an integer division and multiplication operation:

date_trunc('hour', val) + date_part('minute', val)::int / 5 * interval '5 min'

Alternative Methods

Two alternative methods exist for truncating timestamps to 5-minute intervals:

Method 1: Epoch Arithmetic

This method calculates the timestamp by converting it to epoch/unix time, rounding it down to the nearest 5-minute interval, and then converting it back to a timestamp. The following query demonstrates this approach:

SELECT to_timestamp(
    floor(EXTRACT(epoch FROM ht.time) / EXTRACT(epoch FROM interval '5 min'))
    * EXTRACT(epoch FROM interval '5 min')
) FROM huge_table AS ht

Method 2: date_trunc and date_part

This method is similar to the straightforward approach, but it uses date_trunc and date_part separately to achieve the rounding. The following query illustrates this method:

SELECT 
    date_trunc('hour', ht.time) 
    + date_part('minute', ht.time)::int / 5 * interval '5 min'
FROM huge_table AS ht

Performance Comparison

Performance tests on a large table revealed that the straightforward approach outperformed both alternative methods. The results showed:

Method	Run 1 (seconds)	Run 2 (seconds)	Run 3 (seconds)
Epoch Arithmetic	39.368	-	39.526
date_trunc and date_part	34.189	-	37.028

Conclusion

While the alternative methods offer some versatility and simplicity, the straightforward approach using date_trunc and date_part provides the fastest solution for truncating timestamps to 5-minute intervals in Postgres.

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