Re: Serializable read only deferrable- implications

On Tue, 2022-03-08 at 06:29 -0700, Michael Lewis wrote:
> "The DEFERRABLE transaction property has no effect unless the transaction is also
> SERIALIZABLE and READ ONLY. When all three of these properties are selected for a transaction,
> the transaction may block when first acquiring its snapshot, after which it is able to run
> without the normal overhead of a SERIALIZABLE transaction and without any risk of contributing
> to or being canceled by a serialization failure. This mode is well suited for long-running reports or backups."
>
>
> Could anyone expound on the above? What are the real life differences between the two commands below? Would this be applicable at all to sessions on a physical replica?
>
> SET SESSION CHARACTERISTICS AS TRANSACTION ISOLATION LEVEL SERIALIZABLE READ ONLY DEFERRABLE;
>
> SET SESSION CHARACTERISTICS AS TRANSACTION READ ONLY;

A transaction started with the first statement will not take any SI locks, nor
will it ever receive a serialization error.

Yours,
Laurenz Albe
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