Hi,
On 16.11.2016 11:54, cen wrote:
Hi
I am seeking some clarification in regard to full text search across
multiple tables and what the best approach is. Documentation talks about
two approaches when it comes to building a document: on-the-fly concat
of columns and a dedicated tsv column approach. Let's say I want to
perform a search for |"txt1 & txt2 & txt3" on columns table1.col1,
table1.col2 and table2.col1. I see the following solutions:|
|1. Concat all three into a document and perform a FTS.|
|SELECT * FROM (
|
|SELECTto_tsvector(table1.col1)||to_tsvector(table1.col2)||to_tsvector(table2.col1)asdocument
F|||ROM table1 LEFTJOINtable2 ONtable1.table2_id=table2.id| ) subquery
|||WHEREsubquery.document@@to_tsquery(unaccent(?));| |
|2. Create a tsv column in each table, concat tsv columns and perform
FTS on that.|
|SELECT*FROMtable1 LEFTJOINtable2 ONtable1.table2_id=table2.id
WHEREtable1.tsv ||tale2.tsv @@to_tsquery(unaccent(?));|
|3. Have a tsv column only in table1 and insert table2.col1 to the tsv
via triggers. Works but seems very hacky.|
|
|
|It seems to me that option #2 is fast and easy to implement but I am
not sure what the concat of tsvs really means from index usage and
performance standpoint. Option #1 is the most flexible and I'd use that
all the time if it was not THAT much slower than tsv column approacj.
Documentation on TSV columns states: "||Another advantage is that
searches will be faster, since it will not be necessary to redo the
to_tsvector calls to verify index matches."
|
The question is, how much faster are tsv columns really? Are there any
benchmarks about this? If the performance difference is negligible I'd
advocate that using tsv columns is a waste of time and space in most
general cases. But since there is no information on how much faster it's
hard to decide.
I haven't any such benchmarks. But if you have a real database, you can
perform tests using it on your solutions. Because it depends on your
task and what you need.
By the way, I suppose it is better to use COALESCE() function if your
columns could have NULL value:
SELECT * FROM (
SELECT to_tsvector(coalesce(table1.col1,'')) ||
to_tsvector(coalesce(table1.col2,'')) ||
to_tsvector(coalesce(table2.col1,'')) as document FROM table1
LEFT JOIN table2 ON table1.table2_id=table2.id
) subquery WHERE subquery.document @@ to_tsquery(unaccent(?));
And specifying a text search configuration makes queries a little bit
faster:
... to_tsvector('english', coalesce(table1.col1,'')) ...
--
Artur Zakirov
Postgres Professional: http://www.postgrespro.com
Russian Postgres Company
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