Why is the CommandID in PostgreSQL needed

Asked Dec 27 '21 at 16:18

Active Dec 27 '21 at 16:18

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I am struggling to understand why the CommandId (documented here) is necessary in PostgreSQL. The CommandId is sometimes also called cmin and cmax.

I understand that the Transaction ID (xmin/xmax) is necessary. However the cmin/cmax values are documented to only be relevant for the current transaction.

I have been looking around pretty much everywhere, but even the .c/.h files in the PostgreSQL code base do not talk about it a lot.

asked Dec 27 '21 at 16:18

Dave Halter

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See `include/access/htup_details.h` – Adrian Klaver Dec 27 '21 at 17:05
Unfortunately that does not include a better description of `cmin`/`cmax`. I have read this before, but the only thing that helped me a bit was the reference of `combocid.c`. – Dave Halter Dec 28 '21 at 11:12
Short version [cmin/cmax](https://www.postgresql.org/message-id/CAKoxK+6Z248ur31PFMv460OagMOaZBVLRkd7k4bDfmXuUdsE4Q@mail.gmail.com). – Adrian Klaver Dec 28 '21 at 16:14

Why is the CommandID in PostgreSQL needed

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