[Pulp-dev] Performance testing results, autoincrement ID vs UUID primary keys

David Davis daviddavis at redhat.com
Wed Mar 6 14:18:41 UTC 2019

Since there seems to be no objections to switching to UUIDs, I’d like to
propose we merge the PRs[0][1] that will switch core to use UUID PKs
tomorrow (in 24 hours). After that, we'll open redmine issues to update
plugins to use UUIDs.

[0] https://github.com/pulp/pulpcore/pull/16
[1] https://github.com/pulp/pulpcore-plugin/pull/69


On Tue, Mar 5, 2019 at 5:15 PM Jeff Ortel <jortel at redhat.com> wrote:

> +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> 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> 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>
>>> 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> 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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>>>>> Pulp-dev at redhat.com
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