Thread: Phantom read example for new Repeatable Read level

Durumdara wrote:

> Can somebody show me an example for phantom read in "Repeatable
> Read" mode (in 9.1, new, serialized kind of isolation level)?

The repeatable read isolation level did not change in 9.1. Phantom
reads were not possible in repeatable read transactions either before
or after 9.1.

> The help wrote that it is possible:

What help are you talking about?

> What need to do in C1 to read C2's "phantom records"?

It is not possible.

Have you read the documentation on the topic?:

http://www.postgresql.org/docs/9.1/interactive/transaction-iso.html

| When you select the level Read Uncommitted you really get Read
| Committed, and phantom reads are not possible in the PostgreSQL
| implementation of Repeatable Read, so the actual isolation level
| might be stricter than what you select. This is permitted by the
| SQL standard: the four isolation levels only define which phenomena
| must not happen, they do not define which phenomena must happen.

If you want some practical examples of serialization anomalies which
can occur at the repeatable read isolation level which are not
possible at the serializable isolation level, see this Wiki page:

http://wiki.postgresql.org/wiki/SSI

-Kevin

Durumdara wrote:

> What need to do in C1 to read C2's "phantom records"?

After posting a reply I remembered another recent thread which was
more-or-less on the same topic, but with a different slant. Perhaps
you would also find that useful:

http://archives.postgresql.org/pgsql-general/2012-11/msg00166.php

-Kevin