sorting - Changing data organization on disk in MySQL -


we have data set static in mysql database, read times terrible (even indexes on columns being queried). theory since rows stored randomly (or in order of insertion), disk head has scan around find different rows, if knows due index, instead of reading them sequentially.

is possible change order data stored in on disk can read sequentially? unfortunately, can't add ton more ram @ moment have queries cached. if it's possible change order, can define order within order? in, sort column, sort column if first column equal.

could have indices?

additional details: non-relational single-table database 16 million rows, 1 gb of data total, 512 mb ram, mariadb 5.5.30 on ubuntu 12.04 standard hard drive. virtualized machine using openvz, 2 dedicated core e5-2620 2ghz cpu

create syntax:

create table `events` (   `id` int(11) not null auto_increment,   `provider` varchar(10) default null,   `location` varchar(5) default null,   `start_time` datetime default null,   `end_time` datetime default null,   `cost` int(11) default null,   primary key (`id`),   key `provider` (`provider`),   key `location` (`location`),   key `start_time` (`start_time`),   key `end_time` (`end_time`),   key `cost` (`cost`) ) engine=innodb auto_increment=16321002 default charset=utf8;

select statement takes long time:

select * `events`  `events`.start_time >= '2013-05-03 23:00:00' , `events`.start_time <= '2013-06-04 22:00:00' , `flightroutes`.location = 'chicago'

explain select:

1   simple  events  ref location,start_time location    18  const   3684    using index condition; using

mysql can select one index upon filter (which makes sense, because having restricted results using index cannot determine how such restriction has affected other indices). therefore, tracks cardinality of each index , chooses 1 selective (i.e. has highest cardinality): in case, has chosen location index, typically leave 3,684 records must fetched , filtered using where find match desired range of start_time.

you should try creating composite index on (location, start_time):

alter table events add index (location, start_time)

Comments

Post a Comment

Popular posts from this blog

jquery - How can I dynamically add a browser tab? -

since using iframes house external pages are, accounts "not preferred method" , disallowed sites (flickr, one), want dynamically generate browser tabs. e.g., when user submits form, want dynamically generate tab on browser in response submitted. e.g., might want add new tab url like: http://www.bigsurgarrapata.com/contact how in jquery? you want form target attribute action attribute. http://www.w3schools.com/tags/att_form_target.asp browsers have ultimate control on result of target attribute open new tab value of _blank. <form action="contact_submit.php" target="_blank" method="post">
Read more

node.js - Getting the socket id,user id pair of a logged in user(s) -

i have web application done using node js , in it,i have authentication system requires users log in before can access pages. have 2 pages,the homepage , updates page. from read docs,a new socket id issued when user opens tab in browser. me being admin,i know socket id of logged in user , more so,the socket id,logged in user id pair logged in users. what method can use socket id,logged in user id pair make sure broadcast realtime info users online?.
Read more

keyboard - C++ GetAsyncKeyState alternative -

i using windows.h library's getasynckeystate function define key pushed on keyboard . here program returns int value of pushed key example. #include <iostream> #include <windows.h> using namespace std; int main (){ char i; for(i=8;i<190;i++){ if(getasynckeystate(i)== -32767){ cout<<int (i)<<endl; } } return 0; } but trying make opengl simple game , function appeared slow . there function not need cycle 180 times , if statement . thanks you're trying make opengl game, you're going use glfw. if that's case can away using glfwgetkey() such: if (glfwgetkey(glfw_key_up) == glfw_press) {...} if (glfwgetkey(glfw_key_down) == glfw_press) {...} that method nicely explained in tutorial 6 opengl-tutorial.org . should start first tutorial of beginners tutorials , later intermediate tutorials . if you're going make win32 window can listen wm_keydown or wm_keyup messages , virtua
Read more