1. The Importance of
Indexes in MongoDB
How we increased the loading speed Profile Gliphs and Insights
James Toyer, Lead Software Engineer at Glipho

2. What is Glipho?
 Social network for text
based content
 Aims to better engage
writers and readers
 Original content only
 Not an aggregator
 Automatically share to
Facebook, LinkedIn and
Twitter

3. Insights Page
 Load up the gliphs a writer
has
 Iterate through, and
sum, actions for each gliph
 Load and sum actions for
the writers profile
 This can be over 100 calls to
the database
 We know it’s inefficient but
it does the job for now

4. Insights Document Structure
 Timestamp – when the action took place
 EntityId – identifier of the original entity
 ActionType – the type of the entity (probably should be entity
type)
 Action – the actual action that took place

5. Helpful Error Page
…it’s all gone wrong!

6. Troubleshooting
 CPU spiking? NO
 Memory high? NO
 Disk IO high? NO
 Are there any actual regular hits happening? NO
 Do you know anything? NO
Crack out the code performance tools…

7. Pre-Index performance
• 3 passes on each filter page
• Average time for each page to load = 3.9 seconds
• “ListAll” method calls the database
• “ListAll” is iterated over for each gliph in the database and the profile (in this case ~10 times)
• Average time in “ListAll” 256ms

8. More Troubleshooting
 Is the code doing obviously stupid things? NO
 Has Linq screwed you over again? NO
 Do you trust the driver? PROBABLY
 Check the database
 ~ 400,000 documents (now ~690,000)
 No indexes

9. Know your query
GetMongoQuery code Output

10. Index analysis
Without action field With action field
 Query structure  Query structure
 Query time before index:  Query time before index:
 334ms  409ms
 Index  Index
 Query time after index:  Query time after index:
 >1ms  >1ms

11. Post-Index performance
Pre-index performance Post-index performance
 Page load time:  Page load time:
 3.9s  72ms
 “ListAll” method execution  “ListAll” method execution
time: time:
 256ms  >0.2ms
 Page load time deceased by 98%
 “ListAll” method execution time decreased
by 99%

12. Gliph listings for Writers
 Problems:
 Slow loading
 Sometimes erroring out
 Reasons:
 Indexes were no longer
accurate
 Code had changed
 Solution:
 New indexes
 Remove old indexes

13. What did I learn?
 Know exactly what queries are being run
 Don’t do a “best guess” on an index. Test them out
 Don’t “forget” to add indexes
 Ensure your indexes evolve as your queries do

14. Any Questions?
james@glipho.com
glipho.com/james
@jamestoyer