Hi Team, I have a few questions regarding how Couchbase database system handles concurrent operations on the same document. Please refer to the following example for context: Couchbase Bucket: trans2 Document: POE-1000009261 Questions: Does Couchbase allow concurrent write requests from two …

@graham.pople Thanks for sharing the docs. I had gone through but still not able to get clarity on my point-2. If a CB instance updating a document then how another instance read the same doc simultaneously. How this mechanism works. Thanks, Debasis

Reads and writes of a document are atomic. One always occurs before the other. There is no actual concurrent access, but applications can make “concurrent” accesses without issue.

yes @mreiche , I just want to know how applications are getting accessed when these kind of situation arises. In case of RDBMS if a transaction is getting update and if same time other application trying to read, DB will read from redo entries (before image of that transaction) and share it to the e…

An “update” requires a read followed by a write. Please refer to the couchbase documentation for optimistic locking, pessimistic locking and transactions.

@Debasis_Mallick If you’re doing KV operations: if you’re reading a doc and then writing it, you will generally use optimistic locking to detect modifications from other writers. This works by you providing the document’s CAS value (from the read point) when you write it. If the document has been…

So, ‘readers don’t block writers and writers don’t block readers’ doesn’t apply in the strictest sense, and probably shouldn’t be used, right? It’s not really ‘felt’ because it happens so quickly, but it’s not truly ‘simultaneous’ either—correct?

Reads and writes must be atomic with respect to each other. Reads and writes cannot occur simultaneously. Otherwise the read could return part of the old document and part of the new document. Isn’t this what we all assume? Likewise two writes cannot occur simultaneously. And the last write wins. …

[image] pccb: So, ‘readers don’t block writers and writers don’t block readers’ doesn’t apply in the strictest sense, and probably shouldn’t be used, right? @pccb if we’re talking about KV reads & writes then no this sentence does apply (though I’m not sure on its source). It’s only writers …

thanks @graham.pople When you have two or say five writers trying to write the same document, and any of those tools are not used, I believe the writes are queued, even if only for a fraction of a second, with each write happening one after the other. Is that correct?

Query on Concurrent Access and Reads in Couchbase

Couchbase Server

graham.pople January 8, 2025, 10:37am 2

Hi @Debasis_Mallick
Please see Concurrent Document Mutations | Couchbase Docs.

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Query on Concurrent Access and Reads in Couchbase

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