[Pulp-dev] Performance testing results, autoincrement ID vs UUID primary keys
Jeff Ortel
jortel at redhat.com
Tue Mar 5 22:13:37 UTC 2019
+1 to switching back to UUIDs for the reasons Brian gave.
On 3/1/19 2:23 PM, Brian Bouterse wrote:
> I've finally gotten to read through the numbers and this thread. It is
> a tradeoff but I am +1 for switching to UUIDs. I focus on the
> PostgreSQL UUID vs int case because that is our default database. I
> don't think too much about how things perform on MariaDB because they
> can improve their own performance to catch up to PostgreSQL which
> regularly is performing better afaict. I agree with the assessment of
> 30% ish slowdown in the large unit cases for PostgreSQL. Still, I
> believe the advantages of switching to UUIDs are worth it. Two main
> reasons stick out in my mind.
>
> 1. Our core code and all plugin code will always be compatible with
> common db backends even when using bulk_create()
> 2. We get database sharding with postgresql which you can only do with
> UUID pks. I was advised this years ago by jcline.
>
> Performance and compatibility are a pretty classic trade-off. Overall
> I've found that initial releases launch with less performance and
> improve (often significantly) overtime. Consider the interpreter pypy
> (not pypi). It started "roughly 2000x slower [at initial launch] than
> CPython, to roughly 7x faster [now]" [0]. Launching Pulp 3.0 that is
> 30% slower in the worst-case but runs everywhere with zero
> "db-behavior surprises" I think is worth it. Also conversely, if we
> don't adopt UUIDs, how will we address item 1 pre RC?
>
> @dawalker for the "can we have both" option, we probably can have some
> db-specific codepaths, but I don't think doing an application wide PK
> type change as a setting is feasible to support. The db specific
> codepaths are one way performance improves over time. For the initial
> release, to keep things simple I hope we don't have conditional
> database codepaths (for now).
>
> More discussion on this change is encouraged. Thanks @dalley so much
> for all the detailed investigation!
>
> [0]: https://morepypy.blogspot.com/2018/09/the-first-15-years-of-pypy.html
>
> Thank you,
> Brian
>
> On Fri, Mar 1, 2019 at 2:51 PM Dana Walker <dawalker at redhat.com
> <mailto:dawalker at redhat.com>> wrote:
>
> As I brought up on irc, I don't know how feasible the
> complications to maintenance would be going forward, but I would
> prefer if we could use some sort of settings in order to choose
> uuid or id based on MariaDB or PostgreSQL. I want us to work
> everywhere, but I'm really concerned at the impact to our users of
> a 30-40% efficiency drop in speed and storage.
>
> David wrote up a quick Proof of Concept after I brought this up
> but wasn't necessarily advocating it himself. I think Daniel and
> Dennis expressed some concerns. I'd like to see more people
> discussing it here with reasoning/examples on how doable something
> like this could be?
>
> If it's not on the table, I understand, but want to make sure
> we've considered all reasonable options, and that might not be a
> simple binary of either/or.
>
> Thanks,
>
> --Dana
>
> Dana Walker
>
> Associate Software Engineer
>
> Red Hat
>
> <https://www.redhat.com>
>
> <https://red.ht/sig>
>
>
>
> On Fri, Mar 1, 2019 at 9:15 AM David Davis <daviddavis at redhat.com
> <mailto:daviddavis at redhat.com>> wrote:
>
> I just want to bump this thread. If we hope to make the Pulp 3
> RC date, we need feedback today.
>
> David
>
>
> On Wed, Feb 27, 2019 at 5:09 PM Matt Pusateri
> <mpusater at redhat.com <mailto:mpusater at redhat.com>> wrote:
>
> Not sure if https://www.webyog.com/ Monyog will give a
> free opensource project license. But that might help
> diagnose the MariaDB performance. Monyog is really nice,
> I wish it supported Postgres.
>
> Matt P.
>
> On Tue, Feb 26, 2019 at 7:23 PM Daniel Alley
> <dalley at redhat.com <mailto:dalley at redhat.com>> wrote:
>
> Hello all,
>
> We've had an ongoing discussion about whether Pulp
> would be able to perform acceptably if we switched
> back to UUID primary keys. I've finished doing the
> performance testing and I *think* the answer is yes.
> Although to be honest, I'm not sure that I understand
> why, in the case of MariaDB.
>
> I linked my testing methodology and results here:
> https://pulp.plan.io/issues/4290#note-18
>
> To summarize, I tested the following:
>
> * How long it takes to perform subsequent large (lazy)
> syncs, with lots of content in the database (100-400k
> content units)
> * How long it takes to perform various small but
> important database queries
>
> The results were weirdly in contrast in some cases.
>
> The first four syncs (202,000 content total) behaved
> mostly the same on PostgreSQL whether it used an
> autoincrement or UUID primary key. Subsequent syncs
> had a performance drop of between 30-40%. Likewise,
> the code snippets performed 30+% worse. Sync time
> scaled linearly"ish" with the amont of content in the
> repository in both cases, which was a bit surprising
> to me. The size of the database at the end was 30-40%
> larger with UUID primary keys, 736 MB vs 521 MB. The
> gap would be smaller in typical usage when you
> consider that most content types have more metadata
> than FileContent (what I was testing).
>
> Autoincrement PostgreSQL (left) vs. UUID PostgreSQL
> (right) in diff form
> https://www.diffchecker.com/40AF8vvM
>
> With MariaDB the first sync was almost 80% slower than
> the first sync w/ PostgreSQL, but every subsequent
> sync was as fast or faster, despite the tests of
> specific queries performing multiple times worse.
> Additionally the sync performance did not decrease as
> rapidly as it did under PostgreSQL. With MariaDB, one
> of my test queries that worked fine when backed by
> PostgreSQL ended up hanging endlessly and I had to cut
> it off after 25 or so minutes. [0] I would consider
> that a blocker to claiming we support MariaDB / MySQL.
>
> But overall I'm not sure how to interpret the fact
> that on one hand the real-usage performance is equal
> or better better, and on the performance of some of
> the underlying queries is noticably worse. Maybe
> there's some weird caching going on in the backend, or
> the generated indexes are different?
>
> UUID PostgreSQL (left) vs. UUID MariaDB (right) in
> diff form
> https://www.diffchecker.com/W1nnIQgj
>
> I'd like to invite some discussion on this, but
> nothing I've mentioned seems like it would be a
> problem for going forwards with using UUID primary
> keys in a general sense. If we're all in agreement
> about that engineering decision then we can move
> forwards with that work.
>
> [0] for *some* but not all repository versions. No
> idea what's up there.
>
>
>
>
>
>
>
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