indexing - PostgreSQL manualy change query execution plan to force using sort and sequential access instead of full scan -


i have simple query this:

select  *    t1   f1 > 42         , f2 = 'foo'         , f3 = 'bar' order f4 desc  limit 10 offset 100;

i have index field f4 (for other queries). condition "f1 > 42 , f2 = 'foo' , f3 = 'bar'" not representative , corresponds 70% of records in table t1. it's 2 000 000 records in table , growing every day. query plan explanation query shows using of seq scan entire table , performing ordering , limitation.

is possible postgres perform query way:

  1. iterate through reverse ordered rows using index on field f4.
  2. for each row comparison condition f1 > 42 , f2 = 'foo' , f3 = 'bar' , take if corresponded.
  3. if result set size greater limit stop iterate.

here configurations query planner. can manipulate them change query plan (for case can simple set enable_seqscan = off; query).

but before change planner configuration - check if statistics on table correct , collect them again if needed.


Comments

Post a Comment

Popular posts from this blog

matlab - Deleting rows with specific rules -

i got 20*3 cell array , need delete rows contains "137", "2" , "n:t" origin data: 't' '' '' 'np(*)' '' '' [ 137] '' '' [ 2] '' '' 'are' 'and' 'np(fcc_a1#1)' '' '' '1:t' [ 1200] [0.7052] '' [1.2051e+03] [0.7076] '' 'are' 'and' 'np(fcc_a1#3)' '' '' '2:t' [ 1200] [0.0673] '' [1.2051e+03] [0.0671] '' 'are' 'and' 'np(m23c6)' '' '' '3:t' [ 1200] [0.227...
Read more

php - MySQLi multi_query results for later use -

i using mysqli multi_query work several select statemets @ time. know how handle results, able use them later in code. example: <?php //connection stuff $query = "select name, surname database1;"; $query.= "select car, year, type database2 carid='1';"; $query.= "select product, price database3;"; if ($mysqli->multi_query($query)) { if($result = $mysqli->store_result()) { while($row = $result->fetch_row()) { --> here? } } } ?> <html> <div id='persona'> <?php foreach() { --> print name + surname } ?> </div> <div id='cars'> <?php foreach() { --> print car + year + type } ?> </div> <div id='product'> <?php foreach() { --> print product + price } ?> </div> </html> one more thing, prepared statements not possible when using multiple_query, right? there no benefit in putting unrelated queries in 1 multi ...
Read more