Deadlock with one table - PostgreSQL is doing it right

From: Hans Schou <hans(dot)schou(at)gmail(dot)com>
To: pgsql-general <pgsql-general(at)postgresql(dot)org>
Subject: Deadlock with one table - PostgreSQL is doing it right
Date: 2017-12-21 10:37:05
Message-ID: CAApBw36hmDPXTN44Fxx=CCgTgf+-iDsBzNOTtnF-QaCfAOSncQ@mail.gmail.com
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Hi

FYI - if it has any interest

During my preparation for describing what happens when two processes update
the same row in a table, I came across that PostgreSQL is doing right and
Oracle is doing it wrong.

The situation is a process which get a deadlock, but because it is a
script, it sends a commit anyway. This is bad behavior by humans but that's
how they are.

After both processes commit's the table should be:
i | n
---+---
1 | 11
2 | 21
in Oracle it is:
i | n
---+---
1 | 11
2 | 22

PostgreSQL: https://youtu.be/rH-inFRMcvQ
Oracle: https://youtu.be/l2IGoaWql64

PostgreSQL:
A
select * from t;
begin;
update t set n=n+1 where i=2;

B
begin;
update t set n=n+1 where i=1;
update t set n=n+1 where i=2;

A
update t set n=n+1 where i=1;

B
commit;

A
commit;

best regards
hans

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