PostgreSQL 9.1.23 Documentation
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# E.18. Release 9.1.6

> Release Date: 2012-09-24

This release contains a variety of fixes from 9.1.5. For information about new features in the 9.1 major release, see Section E.24.

## E.18.1. Migration to Version 9.1.6

A dump/restore is not required for those running 9.1.X.

However, you may need to perform `REINDEX` operations to recover from the effects of the data corruption bug described in the first changelog item below.

Also, if you are upgrading from a version earlier than 9.1.4, see Section E.20.

## E.18.2. Changes

- Fix persistence marking of shared buffers during WAL replay (Jeff Davis)

  This mistake can result in buffers not being written out during checkpoints, resulting in data corruption if the server later crashes without ever having written those buffers. Corruption can occur on any server following crash recovery, but it is significantly more likely to occur on standby slave servers since those perform much more WAL replay. There is a low probability of corruption of btree and GIN indexes. There is a much higher probability of corruption of table "visibility maps". Fortunately, visibility maps are non-critical data in 9.1, so the worst consequence of such corruption in 9.1 installations is transient inefficiency of vacuuming. Table data proper cannot be corrupted by this bug.

  While no index corruption due to this bug is known to have occurred in the field, as a precautionary measure it is recommended that production installations `REINDEX` all btree and GIN indexes at a convenient time after upgrading to 9.1.6.

  Also, if you intend to do an in-place upgrade to 9.2.X, before doing so it is recommended to perform a `VACUUM` of all tables while having `vacuum_freeze_table_age` set to zero. This will ensure that any lingering wrong data in the visibility maps is corrected before 9.2.X can depend on it. `vacuum_cost_delay` can be adjusted to reduce the performance impact of vacuuming, while causing it to take longer to finish.

- Fix planner's assignment of executor parameters, and fix executor's rescan logic for CTE plan nodes (Tom Lane)

  These errors could result in wrong answers from queries that scan the same `WITH` subquery multiple times.

- Fix misbehavior when `default_transaction_isolation` is set to `serializable` (Kevin Grittner, Tom Lane, Heikki Linnakangas)

  Symptoms include crashes at process start on Windows, and crashes in hot standby operation.

- Improve selectivity estimation for text search queries involving prefixes, i.e. `word``:*` patterns (Tom Lane)

- Improve page-splitting decisions in GiST indexes (Alexander Korotkov, Robert Haas, Tom Lane)

  Multi-column GiST indexes might suffer unexpected bloat due to this error.

- Fix cascading privilege revoke to stop if privileges are still held (Tom Lane)

  If we revoke a grant option from some role `X`, but `X` still holds that option via a grant from someone else, we should not recursively revoke the corresponding privilege from role(s) `Y` that `X` had granted it to.

- Disallow extensions from containing the schema they are assigned to (Thom Brown)

  This situation creates circular dependencies that confuse pg_dump and probably other things. It's confusing for humans too, so disallow it.

- Improve error messages for Hot Standby misconfiguration errors (Gurjeet Singh)

- Make configure probe for `mbstowcs_l` (Tom Lane)

  This fixes build failures on some versions of AIX.

- Fix handling of `SIGFPE` when PL/Perl is in use (Andres Freund)

  Perl resets the process's `SIGFPE` handler to `SIG_IGN`, which could result in crashes later on. Restore the normal Postgres signal handler after initializing PL/Perl.

- Prevent PL/Perl from crashing if a recursive PL/Perl function is redefined while being executed (Tom Lane)

- Work around possible misoptimization in PL/Perl (Tom Lane)

  Some Linux distributions contain an incorrect version of `pthread.h` that results in incorrect compiled code in PL/Perl, leading to crashes if a PL/Perl function calls another one that throws an error.

- Fix bugs in `contrib/pg_trgm`'s `LIKE` pattern analysis code (Fujii Masao)

  `LIKE` queries using a trigram index could produce wrong results if the pattern contained `LIKE` escape characters.

- Fix pg_upgrade's handling of line endings on Windows (Andrew Dunstan)

  Previously, pg_upgrade might add or remove carriage returns in places such as function bodies.

- On Windows, make pg_upgrade use backslash path separators in the scripts it emits (Andrew Dunstan)

- Remove unnecessary dependency on pg_config from pg_upgrade (Peter Eisentraut)

- Update time zone data files to tzdata release 2012f for DST law changes in Fiji

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