Learn PostgreSQL 12. by Unknown

Author:Unknown
Language: eng
Format: mobi, epub
Published: 2020-10-08T13:27:53+00:00

forumdb=> SELECT current_time, txid_current();

current_time | txid_current

--------------------+--------------

16:52:23.028124+01 | 4814

(1 row)

As you can see from the preceding example, the system has assigned two different transaction identifiers, respectively 4813 and 4814, to every statement, confirming that those statements have executed in different implicit transactions. You will probably get different numbers on your system.

If you inspect the special hidden column xmin in a table, you can get information about what transaction created the tuples; take the following example:

forumdb=> SELECT xmin, * FROM categories;

xmin | pk | title | description

------+----+-----------------------+---------------------------------

561 | 1 | DATABASE | Database related discussions

561 | 2 | UNIX | Unix and Linux discussions

561 | 3 | PROGRAMMING LANGUAGES | All about programming languages

(3 rows)

As you can see, all the tuples in the preceding table have been created by the very same transaction, number 561.

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