Re: Growth planning

> On Oct 4, 2021, at 9:22 AM, Rob Sargent <robjsargent@gmail.com> wrote:
> 
> I think the date-station-channel could "take over" for the station-date.  Naturally the latter is chosen if you give just the two fields, but I would be curious to see how well the former performs given just its first two fields(when station-date doesn't exist).
> 

Interesting result here. Technically it appears you are correct - the date-station-channel index *can* “take over” for the station-date index. Unfortunately, it is about 6x slower (see the EXPLAIN ANALYZE output for the station_date_idx here: https://explain.depesz.com/s/COfy <https://explain.depesz.com/s/COfy> vs the one for the date-station-channel index here: https://explain.depesz.com/s/hgBt <https://explain.depesz.com/s/hgBt>) - using the station_date_idx takes around 2.5 seconds while the date-station-channel index is over 12 seconds, even though it has an apparently simpler execution plan. Perhaps something about the different sizes of the indexes?

The query I used in both cases was this:

SELECT
	to_char(datetime AT TIME ZONE 'UTC','YYYY-MM-DD"T"HH24:MI:SS"Z"') as text_date,
	freq_max10,
	sd_freq_max10,
	rsam
FROM
	data
WHERE datetime>='2021-09-27' 
	AND station=27
	AND channel=‘BHZ'

Which actually includes all three columns (which makes it even more interesting to me that the two column, non-UNIQUE index is preferable), and I ran the query several times both with and without the station-date index to (hopefully) make sure there were no caching issues.

---
Israel Brewster
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Alaska Volcano Observatory 
Geophysical Institute - UAF 
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