Okay, that's it.
Please take a seat and we'll get started.
So Holden is going to talk about automating spark upgrades and also lots of testing in
production.
That's going to be interesting.
Testing in production is the best place to test when the alternative is no tests, which
it often is.
Okay, cool.
So let me know if you can't hear me because I'm very easily distracted and get excited
and I might not notice that I'm not talking directly into the microphone, so please grab
my attention if I screw up.
So yeah, I'm Holden.
My pronouns are she or her.
It's tattooed on my wrist.
Super convenient when I wake up in the morning.
I'm on the Spark PMC.
You can think of this as like having tenure, except it doesn't guarantee I get paid.
It just guarantees that I have work to do, so it's like the shady version of tenure.
And I've worked at a whole bunch of different companies, not super relevant, but I've seen
a lot of mistakes made in production and I have made a lot of mistakes in production
so you can learn from some of my mistakes.
My employer who sent me here, Netflix, is hiring and I would be remiss if I did not
mention that.
They're actually finally hiring remote people after who knows how many years.
I'm a co-author of a bunch of books.
Some of them are related to HPC-ish stuff.
I get the highest royalties on scaling Python with Ray, so I think it's a fantastic book
and everyone should buy several copies with your corporate credit card.
If you don't have a corporate credit card, the internet will provide.
You can follow me on social media and there's lots of pictures of my dog.
If you're into that stuff, there's a lot of complaining about American healthcare.
If you enjoy Shaddenfreude, highly recommend it.
It's great.
I also do a lot of open source live streams.
If you like seeing people struggle with computers, once again, it's great.
You can watch me fail.
The code for today's talk and a lot of my other code is on my GitHub.
You can check it out.
And there will be more pictures of my dog.
In addition to who I am professionally, I'm trans, queer, Canadian, in America on a green
card, I make great life choices.
It was a great time to move to America and part of the broader leather community.
I can make that joke now because I have a green card.
It's slightly more difficult for them to kick me out.
This is not directly related.
There is no secret Canadian code modification tools.
Everything we use is open source.
There's no secret Canadian GitHub alternative.
If you go to GitHub.ca, you don't find...
Actually, I don't know what you find.
Maybe you do find something cool.
I'm imagining you don't.
But this is something that I like mentioning because I think for us who are building big
data products or machine learning things, it's super important that we look around and
we see like, hey, who is on my team?
And if you realize you're hanging out with only Canadians, that's fantastic.
Enjoy the poutine.
But maybe it's time to get some other perspectives.
And if you don't know what poutine is, you're missing out.
You should try it someday.
Cheese curds and gravy and French fries.
Best thing ever.
Okay.
So what is our problem?
And so why do we care about automating upgrades?
So fundamentally, our problem is we have unsupported versions of our big data tools and other data
tools running in production.
And this is a problem because when things go wrong, I get woken up.
I don't like getting woken up to figure out what I did five years ago.
And that's just not fun.
The other option is sometimes I get woken up when I'm trying to focus.
That also, sorry, not woken up, interrupted when I'm trying to focus.
And this is important because we are also getting Spark 4 soon.
That's super exciting, super lovely.
There's going to be all kinds of new breaking API changes.
And that's just going to be so much fun, right?
Like, yeah.
Anyways.
And so I don't know about you, but I'm not looking forward to going back and trying to
figure out all of the different things that I've built over the years and upgrading them,
right?
Like, I know I'm going to have to do it, but that is not the thing that excites me in
my life, which leads into, like, why do we have these problems?
Why do we have old things running in production?
We have it because APIs change and code breaks.
And then people are just like, you know what?
I don't want to upgrade.
Just keep running on the old version.
It totally worked.
It's fine.
What could go wrong?
The other one is like, this isn't fun, right?
I don't know.
Does anyone here wake up in the morning excited to upgrade their API usage?
Yeah.
Okay.
So this is zero people, right?
And the other possibility is, right, like, we could try and keep this old software alive,
but we don't want to.
So, how are we going to work around our problem?
So we're going to use software, and then we're also going to have to deal a little bit with
humans, right?
We're going to do automated code updating.
It's super fun.
So much fun.
If you took a compilers class, this is going to look very familiar.
If you didn't take a compilers class, this is so cool.
AppSection.x3s are really cool.
And we're also going to do automated testing and validation and prod.
So the social problem is much harder.
I am completely unqualified to solve it.
I work with other people who are much better at talking to humans.
They did a fantastic job.
They made newsletters.
They tried to make the project exciting.
That failed.
And then they tried to make the project required.
That failed.
And then we set deadlines.
They slipped.
But for sure, totally, we're definitely going to hit our new deadline for real.
Okay.
And now, let's go and see how else we addressed it.
So the other thing that we did is, like, hey, we have this problem that humans don't want
to do a thing.
What about if we made it so they didn't have to do as much work?
And so that's sort of the approach that we took.
We can automate a bunch of this.
And the other part is, like, so we've got API changes, which we mentioned.
And then the other thing that we have is testing code as a nightmare, especially code that
you inherited and is called untitled underscore seven dot ipod dot notebook.
I don't know what it does, let alone I can't make tests for it.
It's terrible.
So yeah, we have a problem.
We're going to fix it with computers.
Google has a lot of really lovely code mod tools that I saw while I was there.
Super fantastic.
This encouraged some counterproductive behavior.
I don't know if any of you have used Google APIs and watched them change underneath you.
So this is a double-edged sword, and we should heed the warnings before we go, like, super,
super all in on this.
So what are we going to do?
So how are we going to move on?
Basically speaking, we're not going to use regular expressions.
For the most part, there's going to be a few times when regular expressions are like the
simple hacky way, and we're just going to do it.
For Scala, we use ScalaFix.
For Python, we use something called PySparkler.
For SQL, we use SQL Fluff.
And for Java, we looked at it, and we were like, we don't have that many Java pipelines.
Get them to update their code by hand.
It's fine.
We know where they work.
Okay.
So how do we figure out what rules to make?
So we could read the release notes, but they're not very complete.
We could look at the MIMA changes, and so Spark has a binary compatibility checker that
it uses, but, oh, dear God, there is just so, so many things in there.
Or we could do my favorite approach, which is run it in production, see what breaks,
and then fix it afterwards.
So we went with the YOLO approach, which is just like we're going to try migrating some
things as it fails.
We'll add the rules that it turns out we needed to add.
So what do these rules look like?
Today, we're just going to look at Scala and SQL.
If you love Python, you can check out the GitHub repo.
It's got some samples there.
So in ScalaFix, we override this function called fix.
We take an implicit semantic document that's really just the syntax tree, so that's the
parsed version of the source code.
And we specify the things that we're interested in looking in, and then we can write a recursive
function which will match on this tree and generate a patch.
And so here, we can see like, hey, do we see something that's calling the JSON reader?
Because the JSON reader, certainly no one would use that ever, so they cited it was
a great idea to change that API because who has JSON data?
That was a joke, by the way.
Everyone has JSON data.
And so it turns out like, yeah, this actually happens a whole bunch.
So we should write a rule for this.
Do we see someone trying to read JSON data from an RDD?
And if so, this is the path we're going to add.
Now the really cool thing here is that we're matching on a syntax tree to produce new syntax
tree.
I can just say, like, swap this part of the syntax tree for this string, and then underneath
the hood, Scala fixes very smart, turns it into a syntax tree.
Everything's happy.
I'm quite happy.
I've got a bunch of sketchy hacks, and they're all inside of a function, sorry, a library
called utils.
So it's great.
We hide all of our mistakes inside of utils because only nerds look inside of utils.Scala.
Huzzah.
And here you see we're recursing on the tree, and we just return nothing if we don't find
any matches.
SQL very similar, but the AST is a little bit fuzzier because we're using SQL Fluff,
and it has to support a whole bunch of different versions of SQL, not just Spark SQL.
Things are a little fuzzy.
So we go ahead and we look and say, like, hey, do we see someone calling this function
that we know has changed?
If so, go ahead and extract out the part that we care about.
And so we go ahead and we grab the third element because, God, whatever, don't worry
about it.
Magic number, totally fine, no mistakes.
And then we go ahead and we say, like, hey, what is the type of this element?
If it's a keyword and it's cast, we know we're good.
The types are matching.
Everything's fine.
Otherwise, if it's not a keyword and the type is cast, we probably need to go ahead and
change this.
Because the types change.
We actually need to add explicit casts into this function.
And so we go ahead and we check it, and then we say, like, okay, function name, no, if
it's cast, we're fine.
If not, we go ahead and we produce these edits.
Now unfortunately, SQL Fluff isn't quite as amazing.
We can't just give it a string and have everything work.
We have to produce, like, the chunk of the syntax tree.
But this is still better than writing regular expressions, right?
So much better.
So this is totally fine.
Everything's great.
How do we know if it works?
So there's a bunch of different things that we could do.
We could try and make tests, but realistically, that's not going to happen.
What we do is we do side-by-side writes and we use icebergs ability to stage commits.
You can do the same thing with Delta Lake or Lake FS.
They're all open source.
I don't know how to do it with Delta Lake because I haven't used it, but I'm sure that
you can do it.
You might be saying, like, holding this sounds like you're running all of your data pipelines
twice.
Isn't that expensive?
The answer is yes.
Does it catch everything?
The answer is no.
But it's a hell of a lot better than just, right?
We've got hope and a little bit of data, and together, are better than hope alone.
So now we're going to come out and it crashed last night, but it's totally probably going
to work today.
Yeah, thank you.
Thank you.
We see I made a backup copy just in case it fails.
What our demo does is it builds a regular Spark project, and it also makes a copy of
it first.
This is a Spark 2.4 project.
Did I break it?
Hello?
Oh.
Okay.
We're back.
Yay.
Okay, cool.
So you see here we've got everyone's favorite big data example, word count.
And so, okay, this is going to go ahead and it's going to add the Scalifix plugin to our
example.
So we're just going to go ahead and say, like, yes, add Scalifix.
And now it's going to run Scalifix, and it's going to run Scalifix with our additional
rules that we created.
So much fun.
It's probably going to work.
This is where it crashed yesterday.
Everyone sent good vibes to my computer.
Come on.
How's that?
Okay.
You can see I subscribed to printlin debugging.
Oh, well.
And now, so it's run the first set of rules which do automated migrations, and now it's
doing a second set of rules, and the second set of rules warns about things that we didn't
think were important enough to create rules to automatically migrate, but we wanted developers
to be aware of.
And one of them is the group by key function change behavior between Spark 2 and Spark 3,
because who uses group by key?
Turns out everyone, very few people depended on the specific weird behavior, though.
And so it's just warning, like, hey, I see you're doing this, and I applied a regular
expression and I see some, like, bad words, not bad words in that ones that I use, but
bad words in that, like, they're bad.
Okay.
And we say, like, everything's fine.
It says we should review our changes, but we're not going to just, like, real developers.
We're just going to hit enter and see if it works.
And now it's going to go ahead and replace Spark 2.4.8 with Spark 3.3.1, and it's going
to run these two pipelines side by side and compare their output.
And so we will see if the demo finishes, ooh, five minutes left.
Okay.
We'll probably finish inside of five minutes.
If it doesn't, we'll give up on the demo.
That's okay.
So here we see it's running these two pipelines side by side.
You can tell because Spark loves logging.
And it passed.
Yay.
Okay.
And then this, this, okay.
Hmm.
Okay.
Well, this part didn't, and that's how you know it's a real demo, is that it failed at
the final end part where it's copying the jar to a new special location, but that's,
that's okay.
The important part of the demo worked.
So we'll call that mostly a win.
And if we want, actually, yeah.
Okay.
I'm going to go.
Oh, thank you.
My lovely assistant.
And so I wanted you to see that like, yes, this actually did update some code.
So we go here, SRC main Scala, Spark demo project, word count dot Scala.
And then we're going to go ahead and we're going to look at the regular version of this.
Oh, God.
Emax, come on.
Now is not the time.
Eight megs and constantly swapping.
I can make that joke as an Emax user.
Okay.
So here we actually do see like it has made some small changes between the two of them.
And, oh, sorry.
Yeah.
So here we see, for example, we have this old pattern of creating the spark context and
it's been swapped for the new pattern of creating the spark context.
And it's done other similar updates to the code.
And the important thing is it now works.
And this is fantastic.
I think it's really cool.
Thank you.
Hand for my assistant, please.
Thank you.
So I'm super stoked that the demo did not crash.
Unlike last night, I switched it back to I was running a nightly build of the JVM and
not surprisingly that didn't go well.
Okay.
So this is all cool, but like where does this fail?
So this kind of fails when it comes to dependencies, right?
Like we can only update the code that you've got.
We don't rewrite byte code.
We just rewrite source code.
So if you're depending on something that doesn't support the new version of spark, it's not
going to work out.
The good news is for us, we got to this so late that all of our dependencies were upgraded.
So there's something to be said for waiting right until the software goes end of life.
Don't tell the security people.
I said that.
The other one that doesn't work super well with is programming language changes.
In theory, that was actually the original purpose of ScalaFix.
In practice, this didn't work so well for Scala 211 specifically because it's just so
old.
We had a bunch of Scala 211 code.
So in conclusion, you should definitely check out the repo.
It's here.
It's spark-upgrade.
It is in my personal GitHub, but a whole bunch of other people have contributed to it.
They're awesome.
I'm lazy.
I wouldn't do all of this work myself.
Thanks to my employer again for sending me here.
I'm super excited that I get to hang out with a bunch of other nerds.
The good news from this talk is that we haven't made a system so powerful that the spark people
don't care about making breaking API changes.
The bad news is we haven't made a system that's so powerful that we can't just not
care about breaking API changes.
The excellent news is that my dog is cute as fuck.
He's here.
I said that at the end of my talk just in case I'm not allowed to swear.
He's really cute.
His name is Professor Timbit.
I miss him so, so much.
Y'all are lovely, but I miss my dog.
Hopefully there's time for a question, maybe.
Yes?
We can also do...
Thank you.
Thank you all.
Have a couple of minutes for questions.
Thank you very much for the talk.
Very interesting.
One general question out of curiosity.
How long did it take to convert everything?
Because you just showed like, I don't know how big the script was, but I can imagine
just how big the repositories that you guys have.
Totally.
So that's a great question.
It takes a really, really long time to convert everything.
And we actually, internally, we have a whole bunch of different projects.
One of them is a project that goes through all of the repositories because we have a
whole bunch of different repositories, and it generates PRs to these projects.
And that code runs daily.
And it doesn't actually catch everything.
So what we do is we generate the changes, and then, as I mentioned, we sort of did the
YOLO run in production approach to life.
So we'll look at these changes, and especially for SQL, it'll be like, hey, we do this shadow
run.
Does it look like it works?
And if not, we actually flag it for review rather than raising the PR so that we can
go back and say, hey, do I need to add a new rule, or is this a one-off special case where
we'll just have a developer deal with it?
So I know that's not exactly an answer, but several hours.
Okay.
Thanks.
Any other questions?
Yeah.
There's one right there.
No.
How many rules did you end up coming up with for this migration from two to three?
And do you anticipate going from three to four?
What?
Do you anticipate going from three to four?
Oh, yeah.
Okay.
So two questions.
I love them.
I don't remember how many rules we came up with.
For Scala, it wasn't a huge number, and that's because while there are a lot of breaking
API changes in Scala, our usage of the APIs in Scala is more narrow, and so I'm very thankful
for that.
For SQL, I think we ended up with around 20, maybe between 10 and 20.
And for Python, I haven't kept track, mostly because that code has been working really
well, and so some of my other teammates have been working more on the Python side, so I
don't remember how many rules we made there.
But they're all in the GitHub.
As for do we anticipate going from Spark three to four?
Yes.
Probably not like the same month Spark four is released.
I love Spark, and we'll make Spark four available internally, but we're not going to go ahead
and start pushing users to migrate to it right away.
We normally wait a little bit for things to stabilize before we start doing managed migrations
just because it's better for our sanity, and there's more fixes to the code base in general.
Cool.
We got another question.
Any more questions?
Okay.
Cool.
Hazar.
Actually, hold on.
You can keep talking because the next speaker is on the bus.
Oh, okay.
So with the next speaker is on the bus, I'm super excited, and we can go ahead and we can
actually look at more of the changes that it made to the code, which I sort of skimmed
over because I didn't want to eat into the next person's time.
So it's kind of basic, right?
But we can see here, this is the side-by-side for the Scala one, and we can actually go
ahead and what we're going to do is we're going to go outside of our end-to-end, and
we're going to go ahead and we're going to look at some of the other SQL rules.
Oh, fancy.
I don't...
Okay.
Oh, this is so that it's better to read.
Okay.
Cool.
Fantastic.
And we're going to go ahead.
I need my lovely assistant again.
Thank you.
Thank you so much.
Hand for my new lovely assistant.
So here we see one of the things that changed between Spark 2 and Spark 3 is that previously
you would be able to do just an arbitrary cast to things as integers, and even if they
weren't integers, it would do kind of a fuzzy conversion.
But in practice, if you wanted to parse a string as an integer rather than casting
string to an integer, you should use int at.
And so here we see we've got something similar.
We use a lot of print debugging.
It's not great.
But what we do here is we return this lint result, and what it's just doing is it's taking
this expression and swapping it to an int when we see a cast with a data type of int.
So much fun.
There's a lot more rules, but I didn't do a git pull on this because the demo barely
worked, and I was just like, let's not tempt fate and do a git pull because I hadn't tested
the end-to-end demo.
But this is kind of cool.
We've got similar updates to our format string.
Super fun.
Oh, right.
And then char versus string types also got updated.
Super fun there as well.
And where was another one?
I want to find it.
Sorry.
Then we've got, there's a rule down at the bottom.
Oh, no.
Okay.
I guess the rule that I was looking for isn't in this version of the code.
Let's go back to ScalaFix.
So the other cool thing about this, sorry, doot, doot, doot.
So one of the really cool things about ScalaFix, just while we're waiting, is that you can
test your rules.
And so, for example, like, I wrote these accumulators, and this is the old bad style
of writing accumulators, and I was like, okay, let's make sure that it updates to the
new good style of accumulators.
And this is super convenient because I don't have to manually construct syntax trees.
ScalaFix just has built-in functionality for this.
And we see here what this rule does is it actually throws out a bunch of situations.
And it's actually going to generate a bunch of warning messages.
But there's situations where, like, this doesn't directly translate to the new API easily.
So we just told users, like, hey, you need to make a change here.
But we'll get it to compile, and then it'll pass the test, and it'll yell at you because
you're trying to access a null.
It's not perfect.
Like, this is very much like a, how would I say this?
This is a very mediocre rule.
But in practice, we didn't find all that many people were creating accumulators with fixed
values to start at.
But the one that we did see was people creating accumulators that explicitly started at zero
long, and so that we just converted to a long accumulator.
And then the other one that I saw here was I also added some tests to make sure that,
like, I had a rule which was applying itself too eagerly.
So I also created a test which was just, like, make sure that this rule doesn't do anything
if it's not, like, encountering the thing that I wanted it to do.
So we can also make essentially negative tests for AST transformations.
That's super convenient.
How much time do I need to kill?
Do we know how long the bus is going to be?
Okay, cool.
Okay.
So we see another one, the group by key thing that I told you about.
We actually had two different situations.
These are ones that we could automatically rewrite, and so that's what we do here.
And so here we see, like, the situation where someone was explicitly using the column name
in a way which we could detect.
But then we also have the situation where, like, we weren't super sure, and so these
ones we did with a warning.
And so we said, like, hey, this should generate a warning because we don't know for sure what's
going on here.
So we want to generate the warning, but in the other situations where we could do the
full rewrite, we made sure that the full rewrite was able to be applied, which I think is kind
of cool from sort of, like, a point of view of you don't have to get everything right,
and you can, like, add these warnings in places where, like, it's worth it to let people know
their code might not work, but, you know, it's not 100% required.
Um...
Choo-choo-choo.
Cool.
Let's see here.
Ah...
Just a quick interruption.
The next speaker is going to be late.
He texted us that he's still on the bus, so we're letting Holden entertain you.
Oh, I got an idea.
I got an idea.
Hi.
I'm just a speaker.
What does that mean?
Where am I?
Oh.
Yeah, I got a...
I think I got another minute of something fun that I want to talk about if it's okay.
So the other thing that we sort of, like, lost over was the, like, side-by-side comparison
in pipeline runs, right?
And so that's totally really...
I think it's really neat, right?
Like, because it's super important because people don't write tests at the end of the
day, and that makes me sad.
But we've got this pipeline comparison project, and...
Oh, God.
I'm just remembering how ugly this code is.
Please don't judge me.
This code was originally written at a conference and then made it into production, as you can
tell by the fact that it's called domagic.py.
Very sorry.
So yeah, so this domagic.py does a bunch of really interesting and terrible things.
And I was mentioning how we mostly don't do regular expressions, but we do a little bit.
And one of the things is when you've got Spark 2 versus Spark 3 and you've got Scala or Java
code, you're going to need different jars.
Whereas in Python and SQL, like, we could maybe just be using the same files, or we
can use the same files with a little bit of a transformation.
But so for the jars, we use a really nasty, really terrible, regular expression to just
kind of extract what we think the version 3 version of our jar is going to be.
And then this is convenient because we can run it side by side.
And then so we've got sort of different options.
Here we've got it so that you can specify the input table.
But I actually did a hack that I'm super proud of because I'm a bad person.
Where we made this plug-in, Iceberg Spark WAP plug-in, where what we do is, oh god, we
use the Iceberg listener and we output this string any time something happens to the logs.
And so if anyone's touching a table while their job is running, we know what tables
it's worth so we can go back and run our comparison on these two tables.
We actually have some special code that goes ahead and looks at these tables before doing
the comparison and says, if the user updated more than 1,000 partitions worth of data,
just don't bother and tell the user they're responsible for validating their data.
And if they're touching more than 1,000 tables, sorry, 1,000 partitions in a table, they should
really have some reliable tests.
For the people who are touching five or 100, like I get it, untitled underscore seven, it's
great in production.
When you're updating that much data, maybe it's not time to depend on Holden's sketchy
do magic dot py.
So I think this is really cool.
And we're going to go back to our friend Pipeline Compare and down to our friend Table Compare.
And so Table Compare is really basic.
And there's actually an updated version internally that I need to bring out that does better
tolerances.
But we just go ahead and we compare these two tables with sort of traditional drawing,
which is part of why we had this limit on the number of partitions.
Because when we didn't have this limit on the number of partitions and we tried to do
these comparisons with some of the pipelines that ran on all of the user data, everyone
was very sad.
And we took down production.
I hope that part.
Yeah, anyways, there was an incident and I got woken up when we did not have that.
And so, yeah, all kinds of fun.
But you see here the thing, the magic here is the snapshot ID, because the other thing
that we output in our listener is what snapshot IDs we're writing to.
Super convenient.
And Iceberg allows us to read from snapshots even if they never got committed.
There's a new thing in the new version of Iceberg that allows for branching that would
be even better because then we would have named things rather than random git hashes.
But we're not running that and it's also not supported in the really old versions of Spark.
And because we want to do the migrations from the really old to the really new, I went
with sort of the lowest common denominator.
And that's kind of how we ended up there.
Okay, that's all that I had that I thought was interesting.
And I think there was someone else who had something that was interesting.
Do you want to come and do your interesting bit?
Thanks to Holden for filling in.
Does anyone have any questions?
That's that?
Yeah, all right.
First of all, thank you for the talk.
I have a quick question in the summary of your talk.
You also mentioned that if time permits, you might have an overview of the changes coming
in Spark 4.
Do you have this overview?
Yeah, so if you're interested in the changes coming in Spark 4, the place to look is the
Spark Jira.
And there's actually like this meta tracking Jira that's in there.
And you can see sort of like the things that we're planning on coming.
Historically, I would say without naming names, there's a particular vendor that loves to
show up at the last minute with the giant piles of code and just kind of yolo it as
a nice surprise for everyone.
So this Jira will give you a good idea of what's coming.
But my guess is there will be a surprise that we find out about in June, just based on history.
I could be wrong.
Maybe everything is actually planned this time.
That would be a pleasant surprise.
But there's a non-zero chance that there will be something new in June too.
Cool.
Okay.
Take it away, my friend.
Or no, you don't.
Oh, okay.
You've got a USB key.
I think my employer would be mad if I let you plug the USB key into my work laptop.
I enjoy being employed.
No, no.
I just had more time to kill.