Total request time spent in ActiveRecord, views, partials
Too many DB calls
Slow DB calls
Pagination
Indexing
Always index your foreign keys (_id columns) when creating migrations (And make a habit)
Depending on your usage and database: create composite indexes.
Using SQL Explain
Using lol_dba gem to add missing indexes (just foreign keys indexes)
N+1 Queries
Using gem bullet to detect N+1 Queries And missing counter_cache
One way to quickly add counter_cache to existing table.
UPDATE courses
SET enrollments_count = (
SELECT COUNT(*) FROM courses
WHERE course_id = courses.id
)
Rack Mini Profiler and Flamegraph
Select only the columns that you need
select and pluck
Rails Query Cache
Caches identical SQL queries in memory
Busted when you write
Busted when the request is finished
Scoped per thread
New Relic and Rails Panel
Do not order by created_at
Because created_at is not indexed by default and we can use id column instead.
Making Multiple Writes? Use a Transaction
Because Database works very hard every time you commit and it has to resolve that commit with the rest of the system. It makes it a lot easier on the database if you combine those writes into a single transaction because then it only has to do that resolution once at the end of all of them.
Use find_each instead of each when load tons of rows
find_each is slightly slower but it uses less memory.
Database
Profiling
Pagination
Indexing
lol_dbagem to add missing indexes (just foreign keys indexes)N+1 Queries
Using gem
bulletto detect N+1 Queries And missingcounter_cacheOne way to quickly add
counter_cacheto existing table.Rack Mini Profiler and Flamegraph
Select only the columns that you need
selectandpluckRails Query Cache
Caches identical SQL queries in memory Busted when you write Busted when the request is finished Scoped per thread
New Relic and Rails Panel
Do not order by created_at
Because
created_atis not indexed by default and we can useidcolumn instead.Making Multiple Writes? Use a Transaction
Because Database works very hard every time you commit and it has to resolve that commit with the rest of the system. It makes it a lot easier on the database if you combine those writes into a single transaction because then it only has to do that resolution once at the end of all of them.
Use
find_eachinstead ofeachwhen load tons of rowsfind_eachis slightly slower but it uses less memory.