Re: [HACKERS] A design for amcheck heapam verification

Hello!

I like heapam verification functionality and use it right now. So, I'm planning to provide review for this patch, probably, this week.

From my current use I have some thoughts on interface. Here's what I get. 

# select bt_index_check('messagefiltervalue_group_id_59490523e6ee451f',true);
ERROR:  XX001: heap tuple (45,21) from table "messagefiltervalue" lacks matching index tuple within index "messagefiltervalue_group_id_59490523e6ee451f"
HINT:  Retrying verification using the function bt_index_parent_check() might provide a more specific error.
LOCATION:  bt_tuple_present_callback, verify_nbtree.c:1316
Time: 45.668 ms

# select bt_index_check('messagefiltervalue_group_id_59490523e6ee451f');
bt_index_check 
----------------

(1 row)
Time: 32.873 ms

# select bt_index_parent_check('messagefiltervalue_group_id_59490523e6ee451f');
ERROR:  XX002: down-link lower bound invariant violated for index "messagefiltervalue_group_id_59490523e6ee451f"
DETAIL:  Parent block=6259 child index tid=(1747,2) parent page lsn=4A0/728F5DA8.
LOCATION:  bt_downlink_check, verify_nbtree.c:1188
Time: 391194.113 ms


Seems like new check is working 4 orders of magnitudes faster then bt_index_parent_check() and still finds my specific error that bt_index_check() missed. 
From this output I see that there is corruption, but cannot understand:
1. What is the scale of corruption
2. Are these corruptions related or not

I think an interface to list all or top N error could be useful.

> 14 дек. 2017 г., в 0:02, Peter Geoghegan <pg@bowt.ie> написал(а):
>> 
>> This could also test the reproducibility of the tests with a fixed
>> seed number and at least two rounds, a low number of elements could be
>> more appropriate to limit the run time.
> 
> The runtime is already dominated by pg_regress overhead. As it says in
> the README, using a fixed seed in the test harness is pointless,
> because it won't behave in a fixed way across platforms. As long as we
> cannot ensure deterministic behavior, we may as well fully embrace
> non-determinism.
I think that determinism across platforms is not that important as determinism across runs.


Thanks for the amcheck! It is very useful.

Best regards, Andrey Borodin.