Serializable read only deferrable- implications

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От Michael Lewis
Тема Serializable read only deferrable- implications
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Msg-id CAHOFxGrrab_d3sOWy-jZWYVf=teP+u_c2KXYaZeFTqwhOrVS=A@mail.gmail.com
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Ответы Re: Serializable read only deferrable- implications  (Laurenz Albe <laurenz.albe@cybertec.at>)
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https://www.postgresql.org/docs/14/sql-set-transaction.html

"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;



Michael Lewis  |  Database Engineer
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