Problem with default partition pruning

From: "Yuzuko Hosoya" <hosoya(dot)yuzuko(at)lab(dot)ntt(dot)co(dot)jp>
To: "'PostgreSQL Hackers'" <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Cc: "'Amit Langote'" <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
Subject: Problem with default partition pruning
Date: 2019-02-22 08:14:04
Message-ID: 00e601d4ca86$932b8bc0$b982a340$@lab.ntt.co.jp
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Hi,

I found the bug of default partition pruning when executing a range query.

-----
postgres=# create table test1(id int, val text) partition by range (id);
postgres=# create table test1_1 partition of test1 for values from (0) to (100);
postgres=# create table test1_2 partition of test1 for values from (150) to (200);
postgres=# create table test1_def partition of test1 default;

postgres=# explain select * from test1 where id > 0 and id < 30;
QUERY PLAN
----------------------------------------------------------------
Append (cost=0.00..11.83 rows=59 width=11)
-> Seq Scan on test1_1 (cost=0.00..5.00 rows=58 width=11)
Filter: ((id > 0) AND (id < 30))
-> Seq Scan on test1_def (cost=0.00..6.53 rows=1 width=12)
Filter: ((id > 0) AND (id < 30))
(5 rows)

There is no need to scan the default partition, but it's scanned.
-----

In the current implement, whether the default partition is scanned
or not is determined according to each condition of given WHERE
clause at get_matching_range_bounds(). In this example, scan_default
is set true according to id > 0 because id >= 200 matches the default
partition. Similarly, according to id < 30, scan_default is set true.
Then, these results are combined according to AND/OR at perform_pruning_combine_step().
In this case, final result's scan_default is set true.

The modifications I made are as follows:
- get_matching_range_bounds() determines only offsets of range bounds
according to each condition
- These results are combined at perform_pruning_combine_step()
- Whether the default partition is scanned or not is determined at
get_matching_partitions()

Attached the patch. Any feedback is greatly appreciated.

Best regards,
---
Yuzuko Hosoya
NTT Open Source Software Center

Attachment Content-Type Size
default_partition_pruning.patch application/octet-stream 12.5 KB

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