indexing - MongoDB: Combining compound shard key with different compound indexes -


let's have collection shard key of {a:1, b:1}.

alongside index shard key, have index of {a:1, c:1, d:1} - note shard key doesn't prefix index.

if run query specifying values fields a, c, , d, can mongo run combination of both indexes query correct shard , query data using second index? or not possible (perhaps because providing 'a' not sufficient choose correct shard)?

as stated in manual shard key indexes, index can index on shard key or compound index shard key prefix of index.

that means have have index of {a:1, b:1} or compound thereof, before using shard key.

now let's have 2 indexes of {a:1, c:1, d:1} , {a:1, b:1}. can run .explain() on query find out index utilised query. see explain results.

lastly, because query can not utilise shard key not mean not possible executed. means mongos need query shards, sub-optimal. when use shard key in query, able 'jump' directly correct chunk on correct shard.

you may find sharded cluster query router useful read.


Comments

Post a Comment

Popular posts from this blog

php - Wordpress website dashboard page or post editor content is not showing but front end data is showing properly -

Image
recently have uploaded wordpress site onto server. have uploaded wordpress site in sub-folder under root folder ../root(domain root folder)/wordpress (where host wordpress folder). now problem content data in page or post in dashboard of wordpress admin panel not showing - see image. but data showing in front view - see image. if not browser cache issue , not issue happened tinymce editor during upgrade; try add config file: define('concatenate_scripts', false);
Read more

How to get the ip address of VM and use it to configure SSH connection dynamically in Ansible -

i trying ip address of vm , trying use establish ssh vm. following script: --- - hosts: localhost become: yes connection: local gather_facts: false serial: 1 vars_files: - createvmvars.yml tasks: - name: gathering vm info. vsphere_guest: vcenter_hostname: "{{vcenter_hostname}}" username: "{{vcenter_username}}" password: "{{vcenter_password}}" guest: "{{guest_name}}" vmware_guest_facts: yes register: var - debug: msg="{{var.ansible_facts.hw_eth0.ipaddresses[0]}}" - name: establishing ssh connection. script: /home/shasha/devops/scripts/ssh_configure.sh "{{var.ansible_facts.hw_eth0.ipaddresses[0]}}" following content of ssh_configure.sh : #!/bin/sh ssh-keygen -t rsa ssh-copy-id $1 but when running playbook, getting following error while executing third task: error! 'var' undefined but debug module(second task) printin
Read more

javascript - Get parameter of GET request -

i make request: createxhrrequest( "get", fileurl, function( err, response ) { if( err ) { alert( "error get!" ); } alert(response); }); and full response: { "status" : "ok", "message" : "jvberi0xljqkjdduxdgkmy how can jvberi0xlj ? i try response.message , response["message"]. nothing works. just simple access this: var json = json.parse(response); json.message
Read more