PostgreSQL 9.0.4 Documentation
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# E.4. Release 9.0.1

> Release Date: 2010-10-04

This release contains a variety of fixes from 9.0.0. For information about new features in the 9.0 major release, see Section E.5.

## E.4.1. Migration to Version 9.0.1

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

## E.4.2. Changes

- Use a separate interpreter for each calling SQL userid in PL/Perl and PL/Tcl (Tom Lane)

  This change prevents security problems that can be caused by subverting Perl or Tcl code that will be executed later in the same session under another SQL user identity (for example, within a `SECURITY DEFINER` function). Most scripting languages offer numerous ways that that might be done, such as redefining standard functions or operators called by the target function. Without this change, any SQL user with Perl or Tcl language usage rights can do essentially anything with the SQL privileges of the target function's owner.

  The cost of this change is that intentional communication among Perl and Tcl functions becomes more difficult. To provide an escape hatch, PL/PerlU and PL/TclU functions continue to use only one interpreter per session. This is not considered a security issue since all such functions execute at the trust level of a database superuser already.

  It is likely that third-party procedural languages that claim to offer trusted execution have similar security issues. We advise contacting the authors of any PL you are depending on for security-critical purposes.

  Our thanks to Tim Bunce for pointing out this issue (CVE-2010-3433).

- Improve `pg_get_expr()` security fix so that the function can still be used on the output of a sub-select (Tom Lane)

- Fix incorrect placement of placeholder evaluation (Tom Lane)

  This bug could result in query outputs being non-null when they should be null, in cases where the inner side of an outer join is a sub-select with non-strict expressions in its output list.

- Fix join removal's handling of placeholder expressions (Tom Lane)

- Fix possible duplicate scans of `UNION ALL` member relations (Tom Lane)

- Prevent infinite loop in ProcessIncomingNotify() after unlistening (Jeff Davis)

- Prevent show_session_authorization() from crashing within autovacuum processes (Tom Lane)

- Re-allow input of Julian dates prior to 0001-01-01 AD (Tom Lane)

  Input such as `'J100000'::date` worked before 8.4, but was unintentionally broken by added error-checking.

- Make psql recognize `DISCARD ALL` as a command that should not be encased in a transaction block in autocommit-off mode (Itagaki Takahiro)

- Update build infrastructure and documentation to reflect the source code repository's move from CVS to Git (Magnus Hagander and others)

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