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Jepsen: Amazon RDS for PostgreSQL 17.4

jepsen.io

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Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#51

Post by altairprime »

tibbar wrote: post #3

The submitted title buries the lede: RDS for PostgreSQL 17.4 does not properly implement snapshot isolation.

I emailed the mods and asked them to change it to this phrase copy-pasted from the linked article:

> Amazon RDS for PostgreSQL multi-AZ clusters violate Snapshot Isolation

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#52

Post by kevincox »

film42 wrote: post #50

I think AWS will need to update their documentation to communicate this. Will a snapshot isolation fix introduce a performance regression in latency or throughput? Or, maybe they stand by what they have as being strong enough. Either way, they'll need to say something.

I think the ideal solution from AWS would be fixing the bug and actually providing the guarantees that the docs say that they do.

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#53

Post by vlovich123 »

cr3ative wrote: post #5

This is in such a thick academic style that it is difficult to follow what the problem actually might be and how it would impact someone. This style of writing serves mostly to remind me that I am not a part of the world that writes like this, which makes me a little sad.

Have you tried using an LLM? I’ve found good results getting at the underlying concepts and building a mental model that works for me that way. It makes domain expertise - that often has unique terminology for concepts you already know or at least know without a specific name - more easily accessible after a little bit of a QA round.

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#54

Post by n2d4 »

belter wrote: post #34
tibbar wrote: post #3

The submitted title buries the lede: RDS for PostgreSQL 17.4 does not properly implement snapshot isolation.

And your comment also...In Multi-AZ clusters. Well this is from Kyle Kingsbury, the Chuck Norris of transactional guarantees. AWS has to reply or clarify, even if only seems to apply to Multi-AZ Clusters. Those are one of the two possibilities for RDS with Postgres. Multi-AZ deployments can have one standby or two standby DB instances and this is for the two standby DB instances. [1] They make no such promises in the…

> They make no such promises in their documentation. Their 5494 pages manual on RDS hardly mentions isolation or serializable

Well, as a user, I wish they would mention it though. If I migrate to RDS with multi-AZ after coming from plain Postgres (which documents snapshot isolation as a feature), I would probably want to know how the two differ.

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#56

Post by xmodem »

Thaxll wrote: post #32
henning wrote: post #2

I thought this kind of bullshit was only supposed to happen in MongoDB!

Those memes are 10 years old, you know that some very tech company use MongoDB right? We're talking billions a year.

Billion dollar companies lose their customer’s data all the time.

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#58

Post by film42 »

kevincox wrote: post #52
film42 wrote: post #50

I think AWS will need to update their documentation to communicate this. Will a snapshot isolation fix introduce a performance regression in latency or throughput? Or, maybe they stand by what they have as being strong enough. Either way, they'll need to say something.

I think the ideal solution from AWS would be fixing the bug and actually providing the guarantees that the docs say that they do.

I agree, but I have a feeling this isn't a small fix. Sounds like someone picked a mechanism that seemed to be equivalent but is not. Swapping that will require a lot of time and testing.

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#59

Post by zaphirplane »

kevincox wrote: post #52
film42 wrote: post #50

I think AWS will need to update their documentation to communicate this. Will a snapshot isolation fix introduce a performance regression in latency or throughput? Or, maybe they stand by what they have as being strong enough. Either way, they'll need to say something.

I think the ideal solution from AWS would be fixing the bug and actually providing the guarantees that the docs say that they do.

Yet bellow your comment is a quote that this is since v13 and above is a comment that there is no mention in the docs.

Using the words Bug and guarantee is throwing the casual readers off the mark ?

Re: Jepsen: Amazon RDS for PostgreSQL 17.4

#60

Post by aphyr »

tibbar wrote: post #3

The submitted title buries the lede: RDS for PostgreSQL 17.4 does not properly implement snapshot isolation.

Folks on HN are often upset with the titles of Jepsen reports, so perhaps a little more context is in order. Jepsen reports are usually the product of a long collaboration with a client. Clients often have strong feelings about how the report is titled--is it too harsh on the system, or too favorable? Does it capture the most meaningful of the dozen-odd issues we found? Is it fair, in the sense that Jepsen aims to be an honest broker of database safety findings? How will it be interpreted in ten years when people link to it routinely, but the findings no longer apply to recent versions? The resulting discussions can be, ah, vigorous.

The way I've threaded this needle, after several frustrating attempts, is to have a policy of titling all reports "Jepsen: ". HN is of course welcome to choose their own link text if they prefer a more descriptive, or colorful, phrase. :-)

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