Comments on: PostgreSQL: Understand the Proof of MVCC (Use XMIN Column) https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/ BIGData | NoSQL | MSSQL | MySQL | PostgreSQL Tue, 20 Aug 2019 10:37:00 +0000 hourly 1 https://wordpress.org/?v=7.0.4 By: Hongjie zhang https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-7704 Tue, 20 Aug 2019 10:37:00 +0000 https://www.dbrnd.com/?p=6838#comment-7704 I think if you want to verify that ‘a new row created when updating’, you should use ‘ctid’.

]]> By: Anvesh Patel https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-6097 Thu, 21 Dec 2017 09:01:41 +0000 https://www.dbrnd.com/?p=6838#comment-6097 thanks for info, I will look into this.
just tested got unique xmin in my database.

]]> By: Pisey https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-6096 Thu, 21 Dec 2017 07:45:32 +0000 https://www.dbrnd.com/?p=6838#comment-6096 xmin:
The identity (transaction ID) of the inserting transaction for this row version. (A row version is an individual state of a row; each update of a row creates a new row version for the same logical row.)

https://www.postgresql.org/docs/9.1/static/ddl-system-columns.html

]]> By: Pisey https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-6095 Thu, 21 Dec 2017 07:03:21 +0000 https://www.dbrnd.com/?p=6838#comment-6095 thank you then

]]> By: Anvesh Patel https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-6094 Thu, 21 Dec 2017 06:56:19 +0000 https://www.dbrnd.com/?p=6838#comment-6094 Thanks for checking…
actually, old xmin becoming frozen so not sure about this.
I need more RND on this.

]]> By: Pisey https://www.dbrnd.com/2017/12/postgresql-understand-the-proof-of-mvcc-use-xmin-column/#comment-6093 Thu, 21 Dec 2017 03:20:16 +0000 https://www.dbrnd.com/?p=6838#comment-6093 Hi, thank you for this, but i still don’t understand when i tried to select xmin from my table(107 rows)
i saw the XMIN is duplicated many rows. Does it mean those rows which have the same XMIN is a concurrent row access?
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select xmin,* from employees;

2595 199 Douglas Grant DGRANT 650.507.9844
2595 200 Jennifer Whalen JWHALEN 515.123.4444
2595 201 Michael Hartstein MHARTSTE 515.123.5555
2595 202 Pat Fay PFAY 603.123.6666
2595 203 Susan Mavris SMAVRIS 515.123.7777
2595 204 Hermann Baer HBAER 515.123.8888
2595 205 Shelley Higgins SHIGGINS 515.123.8080
2595 206 William Gietz WGIETZ 515.123.8181
2595 100 Steven King SKING 515.123.4567
2595 101 Neena Kochhar NKOCHHAR 515.123.4568
2595 102 Lex De Haan LDEHAAN 515.123.4569
2595 103 Alexander Hunold AHUNOLD 590.423.4567
2595 104 Bruce Ernst BERNST 590.423.4568
2595 105 David Austin DAUSTIN 590.423.4569
2595 106 Valli Pataballa VPATABAL 590.423.4560
2595 107 Diana Lorentz DLORENTZ 590.423.5567
2595 108 Nancy Greenberg NGREENBE 515.124.4569
2595 109 Daniel Faviet DFAVIET 515.124.4169
2595 110 John Chen JCHEN 515.124.4269
2595 111 Ismael Sciarra ISCIARRA 515.124.4369
2595 112 Jose Manuel Urman JMURMAN 515.124.4469
2595 113 Luis Popp LPOPP 515.124.4567
2595 114 Den Raphaely DRAPHEAL 515.127.4561
2595 115 Alexander Khoo AKHOO 515.127.4562
2595 116 Shelli Baida SBAIDA 515.127.4563
2595 117 Sigal Tobias STOBIAS 515.127.4564
2595 118 Guy Himuro GHIMURO 515.127.4565

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