PostgreSQL 9.3.4 Documentation
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# E.37. Release 9.0.9

> Release Date: 2012-08-17

This release contains a variety of fixes from 9.0.8. For information about new features in the 9.0 major release, see Section E.46.

## E.37.1. Migration to Version 9.0.9

A dump/restore is not required for those running 9.0.X.

However, if you are upgrading from a version earlier than 9.0.6, see Section E.40.

## E.37.2. Changes

- Prevent access to external files/URLs via XML entity references (Noah Misch, Tom Lane)

  `xml_parse()` would attempt to fetch external files or URLs as needed to resolve DTD and entity references in an XML value, thus allowing unprivileged database users to attempt to fetch data with the privileges of the database server. While the external data wouldn't get returned directly to the user, portions of it could be exposed in error messages if the data didn't parse as valid XML; and in any case the mere ability to check existence of a file might be useful to an attacker. (CVE-2012-3489)

- Prevent access to external files/URLs via `contrib/xml2`'s `xslt_process()` (Peter Eisentraut)

  libxslt offers the ability to read and write both files and URLs through stylesheet commands, thus allowing unprivileged database users to both read and write data with the privileges of the database server. Disable that through proper use of libxslt's security options. (CVE-2012-3488)

  Also, remove `xslt_process()`'s ability to fetch documents and stylesheets from external files/URLs. While this was a documented "feature", it was long regarded as a bad idea. The fix for CVE-2012-3489 broke that capability, and rather than expend effort on trying to fix it, we're just going to summarily remove it.

- Prevent too-early recycling of btree index pages (Noah Misch)

  When we allowed read-only transactions to skip assigning XIDs, we introduced the possibility that a deleted btree page could be recycled while a read-only transaction was still in flight to it. This would result in incorrect index search results. The probability of such an error occurring in the field seems very low because of the timing requirements, but nonetheless it should be fixed.

- Fix crash-safety bug with newly-created-or-reset sequences (Tom Lane)

  If `ALTER SEQUENCE` was executed on a freshly created or reset sequence, and then precisely one `nextval()` call was made on it, and then the server crashed, WAL replay would restore the sequence to a state in which it appeared that no `nextval()` had been done, thus allowing the first sequence value to be returned again by the next `nextval()` call. In particular this could manifest for `serial` columns, since creation of a serial column's sequence includes an `ALTER SEQUENCE OWNED BY` step.

- Fix `txid_current()` to report the correct epoch when not in hot standby (Heikki Linnakangas)

  This fixes a regression introduced in the previous minor release.

- Fix bug in startup of Hot Standby when a master transaction has many subtransactions (Andres Freund)

  This mistake led to failures reported as "out-of-order XID insertion in KnownAssignedXids".

- Ensure the `backup_label` file is fsync'd after `pg_start_backup()` (Dave Kerr)

- Fix timeout handling in walsender processes (Tom Lane)

  WAL sender background processes neglected to establish a SIGALRM handler, meaning they would wait forever in some corner cases where a timeout ought to happen.

- Back-patch 9.1 improvement to compress the fsync request queue (Robert Haas)

  This improves performance during checkpoints. The 9.1 change has now seen enough field testing to seem safe to back-patch.

- Fix `LISTEN`/`NOTIFY` to cope better with I/O problems, such as out of disk space (Tom Lane)

  After a write failure, all subsequent attempts to send more `NOTIFY` messages would fail with messages like "Could not read from file "pg_notify/`nnnn`" at offset `nnnnn`: Success".

- Only allow autovacuum to be auto-canceled by a directly blocked process (Tom Lane)

  The original coding could allow inconsistent behavior in some cases; in particular, an autovacuum could get canceled after less than `deadlock_timeout` grace period.

- Improve logging of autovacuum cancels (Robert Haas)

- Fix log collector so that `log_truncate_on_rotation` works during the very first log rotation after server start (Tom Lane)

- Fix `WITH` attached to a nested set operation (`UNION`/`INTERSECT`/`EXCEPT`) (Tom Lane)

- Ensure that a whole-row reference to a subquery doesn't include any extra `GROUP BY` or `ORDER BY` columns (Tom Lane)

- Disallow copying whole-row references in `CHECK` constraints and index definitions during `CREATE TABLE` (Tom Lane)

  This situation can arise in `CREATE TABLE` with `LIKE` or `INHERITS`. The copied whole-row variable was incorrectly labeled with the row type of the original table not the new one. Rejecting the case seems reasonable for `LIKE`, since the row types might well diverge later. For `INHERITS` we should ideally allow it, with an implicit coercion to the parent table's row type; but that will require more work than seems safe to back-patch.

- Fix memory leak in `ARRAY(SELECT ...)` subqueries (Heikki Linnakangas, Tom Lane)

- Fix extraction of common prefixes from regular expressions (Tom Lane)

  The code could get confused by quantified parenthesized subexpressions, such as `^(foo)?bar`. This would lead to incorrect index optimization of searches for such patterns.

- Fix bugs with parsing signed `hh``:``mm` and `hh``:``mm``:``ss` fields in `interval` constants (Amit Kapila, Tom Lane)

- Use Postgres' encoding conversion functions, not Python's, when converting a Python Unicode string to the server encoding in PL/Python (Jan Urbanski)

  This avoids some corner-case problems, notably that Python doesn't support all the encodings Postgres does. A notable functional change is that if the server encoding is SQL_ASCII, you will get the UTF-8 representation of the string; formerly, any non-ASCII characters in the string would result in an error.

- Fix mapping of PostgreSQL encodings to Python encodings in PL/Python (Jan Urbanski)

- Report errors properly in `contrib/xml2`'s `xslt_process()` (Tom Lane)

- Update time zone data files to tzdata release 2012e for DST law changes in Morocco and Tokelau

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