Re: Serializable Isolation and read/write conflict with index and different keys

[Luca Looz <luca.looz92@xxxxxxxxx>]

I thinking that i have found the culprit. SSI locks leaf pages on the btree index so if the different values are covered by the same page i will get a serialization failure

Is this correct? 

On mer 30 ago 2017, 08:45 Luca Looz <luca.looz92@xxxxxxxxx> wrote:

I have inserted a row that i don't touch, runned ANALYZE and tried again but with the same result.

I'm using postgres 9.6.3 and EXPLAIN ANALYZE shows this:

 Index Scan using users_username_idx on users  (cost=0.13..8.14 rows=1 width=4) (actual time=0.020..0.020 rows=0 loops=1)

   Index Cond: (name = 'bob'::text)

2017-08-30 0:13 GMT+02:00 Thomas Munro <thomas.munro@xxxxxxxxxxxxxxxx>:

On Wed, Aug 30, 2017 at 4:28 AM, Luca Looz <luca.looz92@xxxxxxxxx> wrote:
> I'm trying to use the serializable isolation but i'm getting read/write
> dependencies error even if i have an unique index on the column used and the
> transactions are using different keys.
> For an example see this gist:
> https://gist.github.com/nathanl/f98450014f62dcaf0405394a0955e18e
> Is this an expected behavior?

Take a look at the EXPLAIN plan for the SELECT.  You'll get fine
grained SIREAD locks if it's doing a btree index scan, but table-level
SIREAD locks for other kinds of plans.  Sometimes simple SSI tests can
show a lot of false positives just because of empty tables or missing
statistics (ANALYZE).

--
Thomas Munro
http://www.enterprisedb.com