Making Near-Zero Downtime Deployments Easier

I continue my series on developing for near-zero downtime deployments:

By default, SQL Server uses pessimistic locking, meaning that readers can block writers, writers can block readers, and writers can block writers. In most circumstances, you can switch from Read Committed to Read Committed Snapshot Isolation and gain several benefits. RCSI has certainly been in the product long enough to vet the code and Oracle has defaulted to an optimistic concurrency level for as long as I can remember.

The downtime-reducing benefit to using RCSI is that if you have big operations which write to tables, your inserts, updates, and deletes won’t affect end users. End users will see the old data until your transactions commit, so your updates will not block readers. You can still block writers, so you will want to batch your operations—that is, open a transaction, perform a relatively small operation, and commit that transaction. I will go into batching in some detail in a later post in the series, so my intent here is just to prime you for it and emphasize that Read Committed Snapshot Isolation is great.

Now that I have the core concepts taken care of, the next posts in the series move into practical implementation examples with a lot of code.

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