On Wed, Oct 29, 2014 at 8:05 PM, David Johnston <david.g.johns...@gmail.com> wrote:
> On Wed, Oct 29, 2014 at 11:53 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > >> Jorge Arevalo <jorgearev...@libregis.org> writes: >> >> > This is the result of EXPLAIN ANALYZE >> >> > QUERY >> > PLAN >> > >> ------------------------------------------------------------------------------------------------------------------------------------------------- >> > Index Scan using table1_pkey on table1 (cost=67846.38..395773.45 >> > rows=8419127 width=88) (actual time=7122.704..22670.680 rows=8419127 >> > loops=1) >> > InitPlan 2 (returns $1) >> > -> Result (cost=67846.29..67846.29 rows=1 width=0) (actual >> > time=7009.063..7009.065 rows=1 loops=1) >> > InitPlan 1 (returns $0) >> > -> Seq Scan on table2 p (cost=0.00..67846.29 rows=12689 >> > width=20) (actual time=14.971..5069.840 rows=2537787 loops=1) >> > Filter: (f3 = field7) >> >> Hm. If I'm reading that right, you're building an array containing >> 2537787 entries, each of which is a composite datum containing two >> columns of unmentioned datatypes. I suspect a big chunk of your >> runtime is going into manipulating that array -- PG is not terribly >> efficient with big arrays containing variable-width values. >> >> The seq scan over table2 is for finding entries in table2 (which contains 2537787) that matches a condition using a column from table1 (entries that match table1.field7 = table2.f3). But the array isn't going to contain all the entries, Just a few of them. I think the time is being used in scanning table2 for all the rows of table1 (plus than 8 million). > I'm also a bit confused as to why the planner is saying that the (SELECT >> ARRAY(...)) bit is an InitPlan and not a SubPlan. That implies that >> "field7" in the innermost WHERE clause is not a reference to table1 but a >> reference to table2. Is that really what you meant? IOW, are you sure >> this query is performing the right calculation in the first place? >> >> > I thought the InitPlan was in place because the planner choose to execute > the correlated subquery as a standalone query since it realizes that it is > going to have to end up processing the entire table anyway due to the lack > of a filter on the outer query. In effect executing "table1 JOIN (table2 > subquery) ON (f3 = field7)". > > David J. > > Yes, for each row of table1, table2 is being scanned, to find all the entries that satisfy table1.field7 = table2.f3. Sounds that a really heavy task. I guess I should avoid it, right? BTW, Tom, this is the query with all the parentheses/brackets SELECT value1,value2,value3,value4, value5, hstore(ARRAY['field9', 'field10', 'field11', 'field12', 'field13', 'field14'], ARRAY[field9, field10, field11, field12, field13, field14]) as metadata, value7, (select array((select row(f1, f2) from table2 p where p.f3 = field7))) as values_array FROM table1 Oh, and sorry for the top posting! -- Jorge Arevalo Freelance developer http://about.me/jorgeas80
