---
title: Rails Performance Tips and Tricks
slug: rails-performance-tips-and-tricks
published_at: 2023-09-22 12:00:17 +0000
updated_at: 2026-03-04 20:12:57 +0000
summary: 
description: Working through some performance improvements to a kanban list of projects. We'll cover eager loading, counter caches, improved caching for calculated fields, fragment caching, and image lazy loading.  Here's my perf playbook: https://www.cjav.dev/articles/rails-performance-playbook   #rubyonrails #ruby #rails
tags: [cjav_dev, web development tutorials, web development for beginners, vim, ruby, rails, javascript, ruby on rails, active record, ruby on rails tutorial, performance, counter_cache, caching, fragment caching]
views: 3642
author: CJ Avilla
url: https://www.cjav.dev/videos/rails-performance-tips-and-tricks
youtube_url: https://www.youtube.com/watch?v=Krkh0IGTYrQ
youtube_id: Krkh0IGTYrQ
embed_url: https://www.youtube.com/embed/Krkh0IGTYrQ
thumbnail_url: https://i.ytimg.com/vi/Krkh0IGTYrQ/hqdefault.jpg
type: video
---

# Rails Performance Tips and Tricks

*Published: September 22, 2023*
*Views: 3642*

## Watch

[Watch on YouTube](https://www.youtube.com/watch?v=Krkh0IGTYrQ)

[![Rails Performance Tips and Tricks](https://i.ytimg.com/vi/Krkh0IGTYrQ/hqdefault.jpg)](https://www.youtube.com/watch?v=Krkh0IGTYrQ)

## Description

Working through some performance improvements to a kanban list of projects. We'll cover eager loading, counter caches, improved caching for calculated fields, fragment caching, and image lazy loading.

Here's my perf playbook: https://www.cjav.dev/articles/rails-performance-playbook 

#rubyonrails #ruby #rails

## Transcript

I've got this task that we're going to try to tackle today it's just says the project boards are loading slowly so over here we've got this concept of uh different ways that you can see projects and one of those is in a kanban view it's loading Wicked slow so a couple of ways that we could look at this is if we go to the network Tab and just refresh we can watch this project board thing happening in the waterfall and we can see that well number one it's taken forever and number two we also have a couple other performance monitoring tools set up here you'll notice that we have bullet warnings down here in the left bullet is a nice gem for catching n plus one queries we also have rack mini profiler which is going to be kind of like our main tool today that we're going to use as the metric for driving down this page load time this is kind of cool you can drill in and see what is taking all of the time that's on the page so this is about 11 seconds to load the project boards page and in here we see there are 1800 SQL queries at least firing when we load this page and there's a few happening in the controller and then there's a bunch happening as we work our way through the rendering of this page the first thing that I wanted to do was share this blog post called rails performance Playbook this is just stuff that I think about when I'm trying to optimize performance and yeah so it goes through the back end stuff some front end stuff what I wanted to do today was go through the process of optimizing this page and try to get this load time down to something reasonable that we can actually use so the first thing we want to do is just try to chop off n plus one queries so let's go take a look at the project boards controller and in this controller we have an index action which is checking to see if there's a status type present and if there's a status type then we're going to like grab all of the potential statuses and then we're going to group the projects by that status that's what gives us these sort of columns so by default we're setting up by sales status so lead delivered one hold then there's a bunch of different lost statuses here if we wanted to go by a different status so maybe we go like by the project status that will add a query string parameter and that's going to use different sort of swim Lanes or columns for our kanban view again Wicked slow and really we're only loading up 373 projects here so now it's by project status so unknown scheduling color selection order Supply ready in progress touch-ups this is a bunch of different statuses for the project that's what's Happening Here is we have a bunch of statuses now this is where we try to load all of the projects so we're calling project.kept this is going to exclude any that were discarded so we're using the discard gem to sort of like do soft deletes then we have this includes method which is good because includes will eagerly load some related objects that we need and then we're doing some filtering by assignee by manager and then by projects then we're using that same status type to group projects by that status now one thing that you'll notice is on this page we don't actually have a button to filter by manager or assignee and in fact assignee is a concept we no longer have so I'm going to just speed stuff up by removing that and another thing is that when we look at these cards first of all the image isn't loading that's because these images are on S3 in a production bucket so this is kind of like some sanitized data but we don't actually have the images here one thing that we can do though is I know that this object that's being rendered here is actually the manager and not the assignee and we can tell that by looking at the project boards index so this is the The View that's actually rendering so one of the things that we want to do or like the so the very first thing we're doing here is going through project boards controller and making sure that we're have like we're adding everything to includes that we can that will actually improve the performance of this so that we can decrease the number of queries that are firing includes we'll basically say for all the projects that were returned in this query go and select all of the related locations for all of those projects and go select all of the addresses for those locations and the blobs for the attachments for the assignee Etc so this will kind of like do one query for project for location for address for assignee Avatar and blob instead of one query for all the projects and then every time that we iterate over each of the projects here so when we're going through projects by status yeah so projects by status are all the projects grouped by status as we're iterating over the projects by status maybe we call location.address.short so each project belongs to a location and each location has one address and an address is short method will print out like a short version of what that address looks like what we're doing by calling includes is we're eagerly loading the location all of the location and address objects we're also calling.potential.project type and Dot manager but in this card we're not actually calling a signee anywhere so instead of assignee I actually want this to be a manager and that should immediately sort of like speed up some of this so we'll refresh the page here okay so that chopped off just a couple of SQL queries so that's getting just ever so slightly better another thing that you'll notice when going through the view is that we're calling project dot comments dot count now one thing you might think is oh let's add comments in here so that we're going to fetch the comments as we're going so we could say like comments wait this this count method is still going to fire off unnecessary queries if we were to look at the server log here you'll find that a bunch of these are actually saying select star from comments or comments documentable is the project ID Etc and so a really common tool for avoiding having to go to the database for these comment counts is to use a counter cache so that'll be like the next topic we talk about here so we've gone through all of the includes we're including all of the things that we want to include for each of these cards and now we want to go look at using a counter cache to kill all of these queries so a counter the way that the counter cache works is we create a column in the database that is purely responsible for holding the count of some related sub-object so we'll say it rails G migration add comments count to projects and this you want this to be plural this is actually the table name that you're using and then underscore count that that's like the convention if you happen to name it something else there's ways to get around that but here we'll call it comments count and it's going to be an integer now when we look at the add comments count to projects migration we'll say the default is going to be zero because when you first create a project there are no comments and then what we want to do is we want to iterate over every single project and we want to update the counters for comments yep project.resetc counters will pass in the ID of the project and then we will tell it which counter cache we want to update now when we add this column to the database we also want to make sure that we add the counter cache method to the right Association so we want to find the belongs to side of the association between projects and comments so a comment will belong to a project because a project has many comments if we look at the comment model for a second you'll notice that comment is actually polymorphic you can you can technically have many comments on lots of different objects right now they're just on projects so this should be fines we're going to say counter cache true on the commentable belongs to Association and now what we can do is we'll start by yeah so let's just run this migration rails DB migrate and that will add it to our database one thing to keep in mind is that if you have a massive number of objects that you're adding the counter cache to there is a little bit faster way to do this with raw SQL I like to do it this way it just is more consistent and we really don't have that many projects yet so it's fine even if this was deployed to production now if we look at rails console and we do project DOT first dot comment count sorry that's plural comments count now we get the number one back and if we were to do comments.count you'll notice that this is actually doing count star from comments or comments blah blah blah so the first one using the counter cache only does one query the second one using the association and then the count method on the association does two queries because now we're going to get the count for it so if we were to do like project pluck ID and comments count this would give us like this giant array of arrays where we have the project ID and then how many comments so project 45 has 17 comments project 127 has five comments and so on and so forth what we can do now is go to the the project boards index and go down to our comments count and reset that to comments underscore count and this will use the counter cache and this should be just ever so slightly faster so before it was around 11.8 seconds 11 seconds okay now it says 12.99628 which it technically went up but it should be going a little bit faster so it's possible that was like the first load or something and some stuff is like warming up but one thing that we'll notice is that we went from 1800 ish SQL queries down to 1660. so we're making progress at least on the SQL query front another thing that we can do is if we look at the SQL queries here from rack mini profiler sometimes if there's 1600 of them clicking on this link it can take a second because it's pulling up this list of all the queries that are firing and we're going to get into some knittier nitty-grittier detail here as we're looking at each of these different blocks it tells us where the method is being called that is firing off the query so if we look here when it's rendering the the index.html page inside of one of the blocks the method potential is being called on project on line 337 in project.rb and that's causing this select estimates dot star from estimates where blah blah blah and that in turn is then firing off this other query that's getting estimate items so you can sort of think of an estimate almost like an invoice and estimate items like the items on an invoice and one of the one of the problems here is that potential which is the method that sort of tells us this price here is being recalculated every time so we're going to the database to pull up the pricing model and then we're using this calculator to run and crunch a bunch of numbers for the pricing model which fires off other queries and then we are returning that meth like this this number is being derived every single time rather than being cached and or stored anywhere this is like not stored in the database anywhere as one single number for the project it's just being re-generated every time the project is loaded and that method is here potential so one of the big problems on this page is that we are recalculating these numbers every single time so in the same way that we added comments count we also want to sort of cache things that will cause this potential to fire so in order to do this sort of optimization it makes sense to drill into the methods that are actually being called so let's look at the project model and it was around line 337 so here we go so when we call Dot potential on a project it's going through the estimates Association on the project and calling DOT active and then the sum method in this case is the Ruby sum method that's calling the total on each estimate so let's look at an estimate and there's a total method here that's taking the price minus the discount amount and calling.max and then if we look at the price method here you'll notice that it's using this project estimator passing in the estimate and calling.price on it so if we go to the the project estimator this is now going through each estimates estimate items finding those that have not been discarded and summing up the total and then checking to see if it needs to enforce a minimum and if not then it will just return sort of that sum of estimates otherwise it does another query to the database to look up the price version so now price version defined by whatever so now we're finding finding the price version and the price version model contains minimums for lots of different project types so if the project type is interior then we're going to return this so ultimately price you can see how this price method which is used by the total method which is used by the potential method on Project is doing all this number crunching in real time okay there is a huge benefit to this and that is we avoid an entire class of bugs related to caching so we're gonna buckle up and we're gonna Implement some caching that's gonna store this price rather than calculating it every time we look at it part of the reason we want to do that is that these numbers don't change very often and we can build in a couple different controls and backstops and tools here that will ensure that we keep the price up to date so the way we're going to do this is I'm going to create a new column in the database on estimate for price and we'll probably also create columns in the database for potential and for Revenue so that we can just store these numbers on the project and we can store these numbers on the estimate so price is really the only one that's that we're number crunching every single time on the estimate level and then revenue and potential these are the things that are getting surfaced up one of the benefits of caching the price revenue and potential is that we'll be able to write SQL queries in sort of our business analytics or business intelligence tool to based on the numbers that are on the project or on the estimate directly so that'll be really nice for sort of like our our growth folks so let's start with the estimate and make sure that we can update the price correctly and as the estimate is changed that stays up to date so we'll say rails G migration add price to estimates price as an integer we should never update the price directly it should always be or for for estimates it should always be derived and so there's likely some things we want to set up and make sure that we're protecting like the setter method and things like that but for now we can say this is going to default to zero and similar to the way that we updated the counter cache for projects we'll want to go through the estimate and update to make sure that the price matches what we are setting now this method to set the price is going to be pretty common so on the estimate model itself I want to add a new method down here called price and this will say like it will use the the project estimator tool to give us some calculated price back and if the calculated price does not equal the current price then we'll say self.price is equal to the calculated price okay now we want to update the price before save so before save we're going to say update the price now you'll notice that inside of the update price method here we're not actually updating or not we're not saving it to the database anywhere we're just saying update the price attribute on this model in memory when this method is called so every time we we want to actually update it we'll have to or we'll have to store it to the database so we can say estimate.updateprice.save bang so update price we'll use our project calculator to find the price and then it's going to save it and once this is stored in the database we no longer need this price method down here and we'll just use the price that is stored directly in the database when we're calculating the total or when we're you know doing other other calculations here based on the based on the price but this is the one that's quite expensive because the project estimator requires grabbing a bunch of other related objects and doing things on them okay so before say we want to update the price this should go through and cache the values for the current estimates so we can go look at a specific one right now oh we got a pendering migration all right so let's let's run the migration okay all right now let's open up rails console and see if that worked we can say estimate.last.price and that has some price in it 750 so that seems reasonable let's also refresh our page over here and see if there were any significant changes so now we're going to go from oh 12 seconds down to five seconds so that was a pretty big jump now six seconds now these numbers here are I mean we're still having to go through the project and through all the projects estimates but we're getting much closer and you can see a more even distribution sort of of some of the different pieces here our SQL queries are down from 1800 to less than 500 now if we take a look at the SQL queries we have we still inside of the potential method on Project are firing off a query to all of the estimates and that so that is something that we can improve on one way that we can do that is by oh gosh our turbo streams are freaking out as they're trying to broadcast updates for all the estimates that we just changed in the migration okay before we go do anything on the project level let's make sure that our estimate is actually updating and reflecting the changes as they happen so this estimate right now has dollars and if we go look at the estimate it doesn't have any estimate items yet 750 is the default for this specific type so we're going to add a new estimate item and let's say that this is going to cost I don't know 100 actually let's make it a thousand dollars and so we'll say create and now our estimate should have showed one thousand dollars but it still shows 750. so like this doesn't add up right the amount here 1000 does not add up to 750. so this is the kind of bug that you will introduce when you start caching data in in these saved columns so what we need to do in this case is we want to go over to the estimate item that was the object that we just created and anytime we save any an estimate item we want to make sure that we're touching the estimate so touch true will update the updated at column on the estimate and that's sort of like is a way to say anytime the estimate is uh the estimate item is updated we should also update the related estimate so this touch method though is not going to fire the after save callback that we have here so the touch methods don't trigger the same active record callbacks that will fire when you're updating the object directly so an alternative here is to use the after touch method and if we're going to do an after touch method if we were to call update price that would just again update the price in memory but it wouldn't save it to the database we need to again say save bang after we're touched we want to update the price and save but by adding another estimate item here yeah we'll say we want to I don't know make another estimate item this time for ten dollars when we say create Now by creating this other estimate item that made it so that it touched the estimate and after touch on the estimate it went through and recalculated all of the prices right so we're not just adding the price of the one estimate item that was changing we are fully recalculating the entire estimate and caching the new calculated price so now this correctly is reflected so if we were to delete one of these estimate items if we delete this then that removed the ten dollars also so every time we are like editing or updating the estimate items that is now flowing to the estimate which is awesome so that is going to give us a lot of a lot of benefits because now we can query directly based on on the price for estimates but again that doesn't really solve our problem at this level completely because at the project level which has many estimates we are still calling potential and this potential method is requiring a query so estimates.active so active is this scope on estimates that says find the ones that have not been discarded and where the status is not complete rejected by the customer rejected by internal one of the ways that we can write a query that will give us this data is to use a scope here where we could say let's make a new project scope that's that gives us the projects with the active estimate so we could say scope with active estimates is join estimates and then merge with the active with the active scope so that's a pretty cool handy little thing so now we could say something like project dot with active estimates first and if we look at the query this is actually doing an inner join on estimates now if we were to say give us the potential that's still going to fire a second query here because just by joining we're not actually avoiding that that query all right so the next thing so rather rather than doing it that way what we're going to do is add a revenue and potential method to the project the projects table and then we'll cache those similar to the same way that we did these over here okay so we're going to say rails G migration and revenue and potential to projects Revenue potential and then again we're going to want to go through each of these and say project.update Revenue and update potential and then project.save so we'll make these methods in the projects model here where we will say okay before save update potential and then this will say something like yep okay estimate so this should be estimates DOT active dot sum total and then we'll also say update Revenue yep so Revenue used to pull some Revenue potential use to pull some total and now before we save the project every single time we will update the potential and we will update the revenue and we'll also say after touch we want to do both and we're going to say save Bang there are a lot of things that will touch projects we want to keep track of a pretty solid updated app on projects so a lot of related related associations if you were to add a comment for example it will touch a project if you change an estimate it will touch a project so down here we'll see our project Association has touched true already that's because we want to keep pretty good track of like when when projects have been recently touched all right so after touch we want to update all these details all right let's run this migration rails DB migrate undefined method active for this collection proxy oh this should just be estimates again estimates have many invoices so that's like another confusing layer to this but yeah that's okay so actually speaking of that if we go to the invoice model belongs to estimate touch true we want to make sure that when and invoices changed that touches an estimate and then when touching the estimate that should doesn't necessarily need to update the price but it should we need to make sure that that flows back up to the project so we get the right Revenue all right so this project has an invoice and what we want to do is just see that if updating the invoice it's this is going to fail because the actual invoice is is the ID for the invoice is a production ID so what we can do is open up rails console and say invoice dot find we'll find the one by this ID and we want to say update the status to draft I think and now if we refresh the page here okay so now the paid balance is back to zero so that's good now another thing we can do is like from in the rails console we can look at all the queries that actually fired when we did this so it looked up the invoice by ID in this case it was using Chris Oliver's friendly ID method here then we looked up the account we looked up some other things and ultimately okay once we updated the invoice here that went to touch the project and so here we see this updated app method being updated on the project and same with the estimates so the estimates updated at is also being updated now when those two things were updated we also see these queries that are firing which are being used to look up the values that are going to be cached in the database so if we go find that invoice and its project and now is a project.revenue is zero project.potential is one thousand dollars so now if we update that invoice again to paid we'll see this same sort of thing fire off now what I'm surprised by is we don't see we're not actually seeing the insert or the update for we're not seeing the query that is updating the revenue or potential in the database so project.potential project.revenue okay so that is getting updated project.reload dot Revenue okay so it is getting updated but we don't we're not seeing the query I don't know why yeah I don't know why this project update method is not logging the query that we expect here that's interesting so we should be seeing an update projects set potential and set I wonder if it's we didn't reload rails console or something draft there we go I think I think that was it that we just didn't reload and then if we update it to paid okay so now we're seeing that the revenue is getting set so that's that's awesome that's fantastic okay notice that it was calling both but only actually storing one because only one was changing uh okay so now we should see the number go back to the right amount being paid the balance is all wonky because we're just using fake numbers here and fake money but that is looking good so now if we go back to our projects board we no longer need to query all the way down into the estimates for the for the amounts there so now we're down to four seconds which is great and we only have a handful of SQL queries firing off now in fact there's just one there's probably one like humongous query that's that's happening too early on that's gonna that's gonna collect all the projects here's a bunch of addresses we've got yeah lots of detail coming back from those queries now four seconds though is still not fast enough right like four seconds is still kind of unacceptable for modern stuff okay two seconds that's getting closer for a big big complicated page like this but we can we can do better so the next step that we want to do is now that we've got kind of like some caching going on we've got our eager loading that's the lowest hanging fruit we've got some caching going on for some numbers we're no longer doing a lot of number crunching in real time as the the views are loading another type of caching is Page action or fragment caching so let's talk about how we might do that so from the project boards index.html view right now we have just like this one giant sort of HTML view where we're iterating over each of the statuses again that's like depending on which status we're using then we're iterating over all of the projects by status in this case we're sorting in memory by the Project's title that's also kind of slow so we might be able to improve that and then all the stuff that's happening inside of this iteration is for each project now when we look at this page you can kind of tell like each of these cards is sort of a project component and it's possible that if a project isn't touched for a while and we've kind of like already set up the project negotiated with the client and now we're just waiting to hear back or we're waiting to execute on the project then a lot of these details are not going to change right like the manager is not going to change project type these these numbers on here the name of the project number of comments Etc probably not going to change so we can pretty safely cache this card or like one of these cards and so we're going to use fragment caching to Cache this and so the easiest way that I know to do this is to pull out all of the content of like the the the stuff that's inside of the iteration block and we're going to put it into a partial called card.html.arp and this will have all of the stuff that was previously rendered there and now what we can do is say we want to render render partial of project boards card with the locals of project project and here we can say cached true now sometimes this cash through things works for me sometimes it doesn't I'm not sure there's some details I am missing and don't fully understand about the cached true bit but a more like reliable way that I've done it is to use the cache method here so we can say cash project do and that will this is going to use the fragment caching bits from rails in order to Cache this so then I can remove this cash true thing from here and as the updated app method on this project changes um so every time the project is touched that will bust the cache key for this cache and cause us to have a cash Miss which will re-render and actually call the project board's card method each time and get the get a fresh execution of that partial if we have a cash hit meaning that we've already seen that project once then then we should see that cache hit also happen okay so we'll refresh the page here and right now the first time that we load the page you'll see a whole bunch of output in the server log that says write fragment views slash project board slash Index this index is like a hash of the updated ad slash project slash like the idea of the project and some other stuff some other like timestamp thing so all of this when we see write fragment that means that it's writing to the cache another thing worth mentioning is that when you're in development you can do bin rails bin rails Dev colon cash to toggle development mode caching so development mode caching is no longer on development mode is now caching and that's also restarting the server so let's run it one time that's gonna or now we are reading from the fragments so now we're just saying read fragment instead of right fragment because all these are already cached so if we refresh the page here this should be much faster so now two seconds refresh the page again now we're down to half a second so half a second is not shabby right that's not too shabby two seconds I don't know there's definitely some more things that we can do here right the next the next sort of performance Improvement that we might want to bite off there's a couple but one is that we might want to exclude data from the page that's not actually being used for instance if projects have been complete for a long time we want to remove those from the page okay another thing that's happening on this page now this doesn't matter as much in development because these images are again hosted on they're they're from production AWS buckets but if we inspect each of these images right now you'll see that we have an image with a class and we have a source tag but one feature that we can take advantage of is lazy loading for these images if we go over to our application.hr our application.rb file here we can add lazy load images so we're going to say config dot action view an image loading is lazy okay now if we restart our server and refresh the page ah it's not updating because I have my my Dev cache is on and so it this is actually like this image is cached so this would be a good sort of experiment if we refresh the page now it should be recalculating those images okay so now we see loading is equal to Lazy there so that's going to help a bit with with the speed of the page because now we're going to be lazily loading that okay other little things that you might want to consider is whether or not there's JavaScript running on the page like if you have tons and tons of JavaScript it's going to slow things down again lots of images are going to slow things down if you can limit and remove bits and pieces from the UI that you don't need that'll that'll speed things up a bit also you don't want like tons and tons of Dom elements in there I once maintained a calendar for vacation rental management that was like this giant complex calendar where you could see lots of different dates on these tiny little squares we were rendering like 100 000 Plus elements onto the page and it just slowed the browser down to a crawl it just was not meant to do that so those are some other things to consider you can also do some pagination or other things but I'm pretty happy with where this is at right now I think there might be some other little tweaks and optimizations we do but going from I don't know 12 13 14 seconds down to two feels pretty good for getting this view into a functional state that's going to wrap it up thanks so much for watching and we'll see in the next one

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