Release 7.4.20

PostgreSQL 9.4.12 Documentation
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# E.235. Release 7.4.20

> Release Date: never released

This release contains a variety of fixes from 7.4.19. For information about new features in the 7.4 major release, see Section E.255.

## E.235.1. Migration to Version 7.4.20

A dump/restore is not required for those running 7.4.X. However, if you are upgrading from a version earlier than 7.4.11, see Section E.244.

## E.235.2. Changes

- Fix conversions between ISO-8859-5 and other encodings to handle Cyrillic "Yo" characters (`e` and `E` with two dots) (Sergey Burladyan)

- Fix a few datatype input functions that were allowing unused bytes in their results to contain uninitialized, unpredictable values (Tom)

  This could lead to failures in which two apparently identical literal values were not seen as equal, resulting in the parser complaining about unmatched `ORDER BY` and `DISTINCT` expressions.

- Fix a corner case in regular-expression substring matching (`substring(`string` from `pattern`)`) (Tom)

  The problem occurs when there is a match to the pattern overall but the user has specified a parenthesized subexpression and that subexpression hasn't got a match. An example is `substring('foo' from 'foo(bar)?')`. This should return NULL, since `(bar)` isn't matched, but it was mistakenly returning the whole-pattern match instead (ie, `foo`).

- Fix incorrect result from ecpg's `PGTYPEStimestamp_sub()` function (Michael)

- Fix `DatumGetBool` macro to not fail with gcc 4.3 (Tom)

  This problem affects "old style" (V0) C functions that return boolean. The fix is already in 8.3, but the need to back-patch it was not realized at the time.

- Fix longstanding `LISTEN`/`NOTIFY` race condition (Tom)

  In rare cases a session that had just executed a `LISTEN` might not get a notification, even though one would be expected because the concurrent transaction executing `NOTIFY` was observed to commit later.

  A side effect of the fix is that a transaction that has executed a not-yet-committed `LISTEN` command will not see any row in `pg_listener` for the `LISTEN`, should it choose to look; formerly it would have. This behavior was never documented one way or the other, but it is possible that some applications depend on the old behavior.

- Fix display of constant expressions in `ORDER BY` and `GROUP BY` (Tom)

  An explicitly casted constant would be shown incorrectly. This could for example lead to corruption of a view definition during dump and reload.

- Fix libpq to handle NOTICE messages correctly during COPY OUT (Tom)

  This failure has only been observed to occur when a user-defined datatype's output routine issues a NOTICE, but there is no guarantee it couldn't happen due to other causes.

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