Ask HN: How does Facebook manage object schemas in TAO?

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If Facebook uses an opaque data column in MySQL to represent object data, how do they (1) perform migrations, (2) add/maintain constraints, (3) keep client libraries up-to-date, etc?

I imagine the Facebook graph schema has dozens, if not hundreds, of different object types.

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They have thousands of object types.

I don't know what format they serialize to; native object, XML, json...

But here is an example tool that can do migrations via XML serialized data for Java. As an intermediary step in the XML serialization they create a document of XML that simply contains a version attribute alongside the schema. A similar approach would work for other serialization formats (json, native, etc).

https://dzone.com/articles/migrate-serialized-java

Edit:

I'll bet they use something like Across internally: https://grisha.org/blog/2013/06/06/avro/

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