Re: massive update on gin index - Mailing list pgsql-general

On Sep 14, 2022, at 12:33 , Marcos Pegoraro <marcos@f10.com.br> wrote:

In a table with people's info I have 3 phone numbers, mobile, work and home. But then some have 2 mobiles, some have 2 work numbers, so decided to test it as an array of json. I know I could have another table for that, but I was just testing.

So my original table had

Mobile, Work, Home and all of them are btree indexed.

Then added a jsonb field and updated it with those 3 phone numbers on it

[{"phone": 2236279878, "type": 1}, {"phone": 22998432631, "type": 2}]

[{"phone": 22996783278, "type": 2}]

create index idxPhones on People using gin(Phones)

If I select using old or new fields, both uses index and Execution Time is similar

explain analyze select * from People where Phones @> '[{"phone": 2236279878}]';
explain analyze select * from People where Mobile = 2236279878 or Work = 2236279878 or Home = 2236279878;

 

But then I repeated 2 or 3 times that update which stores those 3 phones on json and then my gin index became slow, very very slow, why ?

select using btree on 3 phone numbers - Execution Time: 0.164 ms

select using gin on json on first update - Execution Time: 0.220 ms

select using gin on json next to 2 or 3 updates - Execution Time: 11.220 ms

And that execution time will come back to 0.220 ms only if I recreate the index.

Then I found gin_pending_list_limit and fast_update which I think are used to update GIN indexes, but didn´t find any examples of both.

What am I missing ? That gin index needs to have some more options or attributes on it ?

I know in a day by day use I'll never do that massive update twice but just to understand when will this index be updated ?

Thanks

Marcos