Consistency

Node failures in Serializeable Snapshot Isolation

Previously in this series: Reading about Serializeable Snapshot Isolation.

Last week I took a deep dive into articles on Serializeable Snapshot Isolation. It ended on a sad note, as I learned that to extended SSI to a sharded database using 2PC for distributed transactions1, there is a need to persist - which means replicate - all read sets in addition to all writes.

This conclusion has been bothering me, so before diving into other papers on distributed serializeable transactions, I wanted to understand better what exactly happens in SSI when a node (shard) fails. This blog doesn't introduce any new papers, just more details. And more speculation.

  • 1. for example, MongoDB

Reading about Serializeable Snapshot Isolation

Previously in this series: Toward strict consistency in distributed databases.

Apparently, when Snapshot Isolation was invented, it was received with great enthusiasm, since it avoids all the anomalies familiar from the SQL standard. It was only as time went by that people discovered that SI had some completely new anomalies and therefore wasn't equivalent to serializeable isolation. (This I learned from the PostgreSQL paper below.)

Toward strict consistency in distributed databases

July is vacation time in Finland. Which means it is a great time to read blogs and papers on consistency in distributed databases! This and following blogs are my reading notes and thoughts. Mostly for my own benefit but if you benefit too, that's great. Note also that my ambition is not to appear like an authority on consistency. I just write down questions I had and things I learned. If you have comments, feel free to write some below. That's part of the point of blogging this!

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