From: | rajan <vgmonnet(at)gmail(dot)com> |
---|---|
To: | pgsql-general(at)postgresql(dot)org |
Subject: | Unable to understand index only scan as it is not happening for one table while it happens for other |
Date: | 2017-06-27 11:09:53 |
Message-ID: | 1498561793525-5968835.post@n3.nabble.com |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-general |
Please help me to understand the following,
*For the following query Index Only Scan to be performance as I am querying
the indexed fields alone. There are 20 fields in this table, inclusive of
the three I am selecting.*
localdb=# explain analyse verbose select uid, guid from mm where uid=100
limit 1;
QUERY
PLAN
------------------------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.27..8.29 rows=1 width=45) (actual time=0.017..0.017 rows=1
loops=1)
Output: uid, guid
-> Index Scan using mm_pkey on public.mm (cost=0.27..8.29 rows=1
width=45) (actual time=0.016..0.016 rows=1 loops=1)
Output: uid, guid
Index Cond: (mm.uid = 100)
Planning time: 0.149 ms
Execution time: 0.042 ms
(7 rows)
*Index only scan runs for the following*
localdb=# explain analyze verbose select id, z from test order by id limit
20;
QUERY PLAN
-----------------------------------------------------------------------------------------------------------------------------------
Limit (cost=0.28..10.29 rows=20 width=17) (actual time=0.017..0.027
rows=20 loops=1)
Output: id, z
-> Index Only Scan using zx on public.test (cost=0.28..1502.47
rows=3000 width=17) (actual time=0.016..0.024 rows=20 loops=1)
Output: id, z
Heap Fetches: 20
Planning time: 0.080 ms
Execution time: 0.050 ms
(7 rows)
-----
--
Thanks,
Rajan.
--
View this message in context: http://www.postgresql-archive.org/Unable-to-understand-index-only-scan-as-it-is-not-happening-for-one-table-while-it-happens-for-other-tp5968835.html
Sent from the PostgreSQL - general mailing list archive at Nabble.com.
From | Date | Subject | |
---|---|---|---|
Next Message | Achilleas Mantzios | 2017-06-27 11:34:59 | Re: Accessing DB2 tables from postgresql |
Previous Message | Swapnil Vaze | 2017-06-27 10:11:39 | Accessing DB2 tables from postgresql |