It's not clear how the validation part works.
For us, we use the schema to validate the incoming data before accepting
and persisting it. We have various disparate producers of data (client
side javascript, internal PHP, other services and languages), and we need
to ensure that the data we receive is consistent and useable in both
loosely and strongly typed systems. Since we are using JSONSchema for
event streams, we have a separate service (EventGate
<https://github.com/wikimedia/eventgate>) that receives the events over
HTTP and validates them before sending them downstream (to Kafka).
Beyond that, what else do you do with JS? Is there
some sort of code
generation aspect to it, as with the proto compiler?
We also use the schema to do downstream integration between data stores.
The JSONSchemas are used to create RDBMS tables into which we can parse and
insert the JSON event data. We also use the JSONSchema to do language
integration. If not code generation directly, some auto
deserializers between a JSON event and Java (or whatever) objects. E.g. map
from JSONSchema to Spark's schema format
<https://github.com/wikimedia/analytics-refinery-source/blob/master/refinery-spark/src/main/scala/org/wikimedia/analytics/refinery/spark/sql/JsonSchemaConverter.scala>,
or (one day?) from JSONSchema to Kafka Connect's schema format
<https://github.com/ottomata/kafka-connect-jsonschema>.
Does a production data consumer validate every
incoming JSON object it
receives?
It could, but usually not. In our usage, we assume that data has been
validated before it enters the system, so consumers can be sure the data is
valid.
The biggest advantage I can see to protos (outside of
the immersive
google infrastructure) is efficiency.
I'm not sure how PB works here, but an advantage of Avro was its schema
evolution features. This makes it easier to allow consumers and producers
to work with different versions of the same schema, without having to
upgrade their code. We accomplish this by only allowing a very strict type
of change to JSONSchemas: only optional field additions are allowed (no
renames, no field removals, no type changes, etc.).
Is mongo used inside of WMF?
Not that I know
of. I could be wrong, but I think most application state
for WMF services is either in MariaDB (MediaWiki uses this) or in Redis or
Cassandra (which are really derivative caches of data canonically stored in
MariaDB).
On Mon, Nov 25, 2019 at 9:00 PM Roy Smith <roy(a)panix.com> wrote:
> Hi Andrew,
>
> Thanks for that info. I've never heard of JSON Schema before. I've done
> a bit of reading on it. As far as I can tell, it's pretty much a 1:1
> mapping to proto specification language. What's not clear to me is how you
> actually use JSON Schema in real life.
>
> I get that it provides documentation of the schema. That's pretty obvious.
>
> It's not clear how the validation part works. Does a production data
> consumer validate every incoming JSON object it receives? Do producers
> validate every object they send?
>
Beyond that, what else do you do with JS? Is there
some sort of code
> generation aspect to it, as with the proto compiler?
>
> Over the past few days, I've been playing with some code a bit, and
> thinking a lot. I'm slowly coming to the conclusion that JSON is the way
> for me to go, for pretty much the reasons you outlined in T198256. The
> biggest advantage I can see to protos (outside of the immersive google
> infrastructure) is efficiency. If I need better performance later,
> swapping out one for the other doesn't seem like it would be a major
> problem.
>
> On a vaguely related note, I saw in the recent Cloud Services Survey, a
> question that mentioned MongoDB. Is mongo used inside of WMF? It seems
> like it would be a natural in a JSON shop. I don't see it running on the
> bastion hosts.
>
> On Nov 25, 2019, at 11:14 AM, Andrew Otto <otto(a)wikimedia.org> wrote:
>
> Hi Roy,
>
> We had to evaluate data formats for event streaming systems as part of
> WMF's Modern Event Platform <https://phabricator.wikimedia.org/T185233>
> program
>
<https://www.mediawiki.org/wiki/Wikimedia_Technology/Annual_Plans/FY2019/TEC2:_Modern_Event_Platform>.
> The event streaming world mostly uses Avro, but there is plenty of
> Protobufs around too.
>
> We ultimately decided to use JSON with JSONSchema as our transport
> format. While lacking some advantages of the other binary options, JSON is
> just more ubiquitous and easier to work with in a distributed and open
> source focused developer community. (You don't need the schema to read the
> data.)
>
> More reading:
> - Choose Schema Tech RFC <https://phabricator.wikimedia.org/T198256>
> - An old JSON justification blog post
> <https://blog.wikimedia.org/2017/01/13/json-hadoop-kafka/>
>
> Our choice of JSONSchema and JSON is mostly around canonical data schemas
> for in-flight data transport and protocols. For data at rest, it might
> make more sense to serialize into something completely different (we use
> Parquet in Hadoop for most data there). You can read some WIP
> documentation about how we use JSONSchema here
> <https://wikitech.wikimedia.org/wiki/Event_Platform/Schemas>.
>
>
>
>
>
>
> On Fri, Nov 22, 2019 at 10:14 PM Roy Smith <roy(a)panix.com> wrote:
>
>> I'm starting to look at some machine learning projects I've wanted to do
>> for a while (ex: sock-puppet detection). This quickly leads to having to
>> make decisions about data storage formats, i.e. csv, json, protobufs, etc.
>> Left to my own devices, I'd probably use protos, but I don't want to be
>> swimming upstream.
>>
>> Are there any standards in wiki-land for how people store data? If
>> there's some common way that "everybody does it", that's how I
want to do
>> it too. Or, does every project just do their own thing?
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