What's the Fastest Way to Truncate Timestamps to 5-Minute Intervals in PostgreSQL?

Truncating Timestamps to 5-Minute Boundaries Efficiently in Postgres

Truncating timestamps is essential for temporal analysis. Postgres offers the date_trunc function, enabling us to round timestamps to various units. However, for truncating to the nearest 5-minute boundary, a more specific approach is required.

Typically, the following straightforward method is employed:

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

However, when performance is critical, it's crucial to explore the fastest solution possible.

Alternative Approach: Going Through Epoch Time

An alternative approach involves converting the timestamp to an epoch timestamp and then truncating it. This method is expressed as:

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 LIMIT 4000000

Benchmarking and Results

To evaluate the performance of both methods, an informal benchmark was conducted against a large table with 4 million rows. The queries were alternated to prevent caching advantages.

Results:

Method	Run 1	Run 3	Run 5
Epoch Time	39.368 seconds	39.526 seconds	39.883 seconds
Hour and Minute	34.189 seconds	37.028 seconds	32.397 seconds

Conclusion

Surprisingly, the method using date_trunc and date_part consistently outperformed the epoch time approach. Despite being more versatile and easier to parameterize, the epoch time method sacrifices some performance for a wider range of time unit truncations.

Therefore, for truncating timestamps to 5-minute boundaries specifically in Postgres, the straightforward method using date_trunc and date_part is the recommended approach.

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