sql - Using a range filter in a greatest-n-per-group subquery has very poor performance -


i've got simple query (being used subquery in greatest-n-per-group situation). state_id primary key - else non-unique.

select max(states.state_id) max_state_id states states.created >= '2017-06-10 21:53:38.977455'   , states.created < '2017-06-26 07:00:00' group states.entity_id;

the problem is, query horrifically slow, , don't believe order of multicolumn index can solve way it's written. ends using where; using index; using temporary; using filesort

in case it's not clear: we're trying here latest state_id each entity_id between 2 timestamps.

we instead max(states.created) (rather max(states.state_id)) better anyway, don't have state_id outer query join on.

here's full query including outer part give full context:

select states.state_id states_state_id, states.domain states_domain, states.entity_id states_entity_id, states.state states_state, states.attributes states_attributes, states.event_id states_event_id, states.last_changed states_last_changed, states.last_updated states_last_updated, states.created states_created states inner join (     select max(states.state_id) max_state_id     states     states.created >= '2017-06-10 21:53:38.977455' , states.created < '2017-06-26 07:00:00' group states.entity_id ) anon_1 on states.state_id = anon_1.max_state_id;

surely there must way rewrite query in such manner allow index loose index scan...

first, query:

select max(s.state_id) max_state_id states s s.created >= '2017-06-10 21:53:38.977455' ,       s.created < '2017-06-26 07:00:00' group s.entity_id;

i want sure have index on states(created, entity_d, state_id). see if help.

second, consider rewriting query as:

select max(s.state_id) max_state_id states s s.created >= '2017-06-10 21:53:38.977455' ,       s.created < '2017-06-26 07:00:00' ,       s.state_id = (select max(s2.state_id)                     states s2                     s2.entity_id = s.entity_id ,                           s2.created >= '2017-06-10 21:53:38.977455' ,                           s2.created < '2017-06-26 07:00:00'                    );

for query, want indexes on: states(entity_id, created, state_id) , states(created, entity_id, state_id) (the order of columns in indexes matters).


Comments

Post a Comment

Popular posts from this blog

php - Vagrant up error - Uncaught Reflection Exception: Class DOMDocument does not exist -

i've set bento/ubuntu-16.04 vagrant box using php 5.6, , getting following error quite few times when try , run shell script: "uncaught reflection exception: class domdocument not exist". i've tried adding following top of script (not together), each no success: "sudo apt-get install php5.6-xml", "sudo apt-get install php5-xml", "sudo apt-get install php-dom" i've tried resetting server "sudo service apache2 restart". does have suggestions?
Read more

vue.js - Create hooks for automated testing -

Image
qa guys complained can't automate frontend testing. because our html looks same outside. lazy hack did this <template> <div :role="$options.name"> ... </div> </template> <script> export default { name: 'vmcomponentname' } </script> which takes name script , applies html. in browser get: <div role="vmcomponentname"> ... </div> line :role="$options.name" goes in every component. is there dry er solutions? please share. additional details i'll explain in details looking for. imagine have vmusercreate form creates user. test case can create user . to automatically test without role, have use following selector: .wrapper > .wrapper > .wrapper > .submit-button the test extremely brittle (will break lot). if use roles can use [role="vmusercreateform"] .submit-button selector. many folds less brittle. so basically, i'm ...
Read more

Add new key value to json node in java -

i have json file : { "id":1, "name":"abc", "addressdetails": { "city":"newyork" } } i wanted add 1 more key-value ("pincode" : "414141") node 'addressdetails'. i tried using : objectmapper mapper = new objectmapper(); jsonnode root = mapper.readtree(new file("d://test.json")); objectnode node = mapper.createobjectnode(); node.with("addressdetails").put("pincode", "414141"); but it's not getting added, there way can ? you can try you should modify file path objectmapper mapper = new objectmapper(); objectnode nodes = mapper.readvalue(new file("d:\\test.txt"), objectnode.class); nodes.with("addressdetails").put("pincode", "414141"); mapper.writer().writevalue(new file("d:\\test.txt"), nodes);
Read more