On Sat, Dec 3, 2016 at 9:32 PM, Steve Atkins <steve@xxxxxxxxxxx> wrote:
> On Dec 3, 2016, at 3:57 PM, Samuel Williams <space.ship.traveller@gmail.com > wrote:
>
> Thanks everyone for your feedback so far. I've done a bit more digging:
>
> MySQL in MBytes (about 350 million rows):
>
> index_user_event_on_what_category_id_created_at_latlng | 22806.00 It's unlikely anyone will be able to usefully answer the questions you
> index_user_event_for_reporting | 18211.00
> index_user_event_on_created_at | 9519.00
> index_user_event_on_user_id | 6884.00
> index_user_event_on_poi_id | 4891.00
> index_user_event_on_deal_id | 3979.00
>
> Postgres (about 250 million rows):
>
> index_user_event_on_what_category_id_created_at_latlng | 25 GB
> index_user_event_for_reporting | 19 GB
> index_user_event_on_created_at | 7445 MB
> index_user_event_on_user_id | 7274 MB
> index_user_event_on_deal_id | 7132 MB
> index_user_event_on_poi_id | 7099 MB
>
> So, the index is a bit bigger, plus there is also the PKEY index which
> increases disk usage by another whole index. Keep in mind in the
> above, MySQL has about 40% more data.
>
> With some indexes, it looks like MySQL might not be adding all data to
> the index (e.g. ignoring NULL values). Does MySQL ignore null values
> in an index? Can we get the same behaviour in Postgres to minimise
> usage? What would be the recommendation here?
should be asking without seeing the schema and index definitions,
and maybe some clues about how you're querying the data.
Cheers,
Steve
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You are comparing apples to oranges. MySQL and PostgreSQL engines are different by design, so likewise
the size of the indexes will be different.
You may as well ask why a 2015 Porsche 911 Carrera 6 cyl, 3.4 L, Auto(AM-S7) gets 22 MPG,
but the 2016 Jaguar XF MPG gets 24 mpg.
--
Melvin Davidson
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.![]()
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
