database performance - SQL Server: Why is SELECT on case insensitive column faster than on case sensitive? -


i use sql server 2016 express , java application jdbc driver version 4.2.

my database has collation of latin1_general_ci_as (case insensitive). table has column of type varchar(128) not null. there unique index on column.

my test scenario follows:

after inserting 150000 strings of 48 characters length 200 selects of randomly chosen, existing strings. measure total execution time of queries.

then drop index, alter table change columns collation latin1_general_cs_as (case sensitive) , create unique index again.

then 200 selects take in total more time.

in both cases (ci , cs) execution plans simple , identical (search using index).

the query execution time not depends on case sensitivity. collation cs grows faster if strings have identical prefixes. here results (execution time in seconds):

+----+---------+------------------+-------------------+-------------------+ |    + rnd(48) + const(3)+rnd(45) + const(10)+rnd(38) + const(20)+rnd(28) + +----+---------+------------------+-------------------+-------------------+ | ci +       6 +                6 +                 7 +                 9 + | cs +      10 +               20 +                45 +                78 + +----+---------+------------------+-------------------+-------------------+

the longer identical prefix of random strings more time case sensitive queries take.

  1. why search on case insensitive column faster on case sensitive column?
  2. what reason identical prefix behavior?


Comments

Post a Comment

Popular posts from this blog

Sort a complex associative array in PHP -

this question has answer here: php sort array subarray value 5 answers i have associative array in php like: $newarray1 = array ( [producta] => array ( [link] => http://sanjosespartan.com/blog/products/agile-java-development/ [visitcount] => 4 ) [productd] => array ( [link] => http://sanjosespartan.com/blog/products/intro-to-go/ [visitcount] => 1 ) [productg] => array ( [link] => http://sanjosespartan.com/blog/products/node-js-for-developers/ [visitcount] => 1 ) [productb] => array ( [link] => http://sanjosespartan.com/blog/products/beginning-mysql/ [visitcount] => 1 ) [productc] => array ( [link] => http://sanjosespartan.com/blog/products/computer-networks/ [visitcount] => 1 ) ...
Read more

vb.net - How to ignore if a cell is empty nothing -

how use roscolor() ignore value (like empty cell) ? color row if value upper 5 when there nothing in cell, want ignore roscolor() apply, how? public sub roscolor() integer = 0 quotedatagridview1.rows.count() - 1 step +1 dim val integer val = quotedatagridview1.rows(i).cells(3).value if val = vbempty quotedatagridview1.rows(i).defaultcellstyle.backcolor = color.white elseif val < 5 quotedatagridview1.rows(i).defaultcellstyle.backcolor = color.red elseif val > 5 , val < 10 quotedatagridview1.rows(i).defaultcellstyle.backcolor = color.lightyellow end if next end sub you can check empty value following public sub roscolor() integer = 0 quotedatagridview1.rows.count() - 1 step +1 dim val = quotedatagridview1.rows(i).cells(3).value if isdbnull(val) or val nothing quotedatagridview1.rows(i).defaultcellstyle.backcolor = color.white ...
Read more

recursion - Can every recursive algorithm be improved with dynamic programming? -

i first year undergraduate csc student looking competitive programming. recursion involves defining , solving sub problems. understand, top down dynamic programming (dp) involves memoizing solutions sub problems reduce time complexity of algorithm. can top down dp used improve efficiency of every recursive algorithm overlapping sub problems? dp fail work , how can identify this? the short answer is: yes. however, there constraints. obvious 1 recursive calls must overlap. i.e. during execution of algorithm, recursive function must called multiple times same parameters. lets truncate recursion tree memoization. can use memoization reduce number of calls. however, reduction of calls comes price. need store results somewhere. next obvious constraint need have enough memory. comes not-so obvious constraint. memory access requires time. first need find result stored , maybe copy location. in cases, might faster let recursion calculate result instead of loading somewher...
Read more