[GENERAL] Re: Unable to understand index only scan as it is not happening forone table while it happens for other

Thanks.

Now I did the same query, but it is going for *index-only scan* only after I
put *limit*

localdb=# explain analyse verbose select uid from mm where uid>100 order by
uid;
                                                       QUERY PLAN

-------------------------------------------------------------------------------------------------------------------------
 Sort  (cost=30.99..31.87 rows=354 width=8) (actual time=0.243..0.294
rows=354 loops=1)
   Output: uid
   Sort Key: mm.uid
   Sort Method: quicksort  Memory: 41kB
   ->  Seq Scan on public.mm  (cost=0.00..16.00 rows=354 width=8) (actual
time=0.010..0.123 rows=354 loops=1)
         Output: uid
         Filter: (mm.uid > 100)
         Rows Removed by Filter: 46
 Planning time: 0.109 ms
 Execution time: 0.342 ms
(10 rows)

localdb=# explain analyse verbose select uid from mm where uid>100 order by
uid *limit 10*;
                                                                       QUERY
PLAN

--------------------------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.27..2.13 rows=10 width=8) (actual time=0.026..0.037 rows=10
loops=1)
   Output: uid
   ->  Index Only Scan using mm_pkey on public.mm  (cost=0.27..65.91
rows=354 width=8) (actual time=0.025..0.034 rows=10 loops=1)
         Output: uid
         Index Cond: (mm.uid > 100)
         Heap Fetches: 10
 Planning time: 0.096 ms
 Execution time: 0.059 ms
(8 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-tp5968835p5968971.html
Sent from the PostgreSQL - general mailing list archive at Nabble.com.