PostgreSQL 9.1.23 Documentation
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# E.1. Release 9.1.23

> Release Date: 2016-08-11

This release contains a variety of fixes from 9.1.22. For information about new features in the 9.1 major release, see Section E.24.

The PostgreSQL community will stop releasing updates for the 9.1.X release series in September 2016. Users are encouraged to update to a newer release branch soon.

## E.1.1. Migration to Version 9.1.23

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

However, if you are upgrading from a version earlier than 9.1.16, see Section E.8.

## E.1.2. Changes

- Fix possible mis-evaluation of nested `CASE`-`WHEN` expressions (Heikki Linnakangas, Michael Paquier, Tom Lane)

  A `CASE` expression appearing within the test value subexpression of another `CASE` could become confused about whether its own test value was null or not. Also, inlining of a SQL function implementing the equality operator used by a `CASE` expression could result in passing the wrong test value to functions called within a `CASE` expression in the SQL function's body. If the test values were of different data types, a crash might result; moreover such situations could be abused to allow disclosure of portions of server memory. (CVE-2016-5423)

- Fix client programs' handling of special characters in database and role names (Noah Misch, Nathan Bossart, Michael Paquier)

  Numerous places in vacuumdb and other client programs could become confused by database and role names containing double quotes or backslashes. Tighten up quoting rules to make that safe. Also, ensure that when a conninfo string is used as a database name parameter to these programs, it is correctly treated as such throughout.

  Fix handling of paired double quotes in psql's `\connect` and `\password` commands to match the documentation.

  Introduce a new `-reuse-previous` option in psql's `\connect` command to allow explicit control of whether to re-use connection parameters from a previous connection. (Without this, the choice is based on whether the database name looks like a conninfo string, as before.) This allows secure handling of database names containing special characters in pg_dumpall scripts.

  pg_dumpall now refuses to deal with database and role names containing carriage returns or newlines, as it seems impractical to quote those characters safely on Windows. In future we may reject such names on the server side, but that step has not been taken yet.

  These are considered security fixes because crafted object names containing special characters could have been used to execute commands with superuser privileges the next time a superuser executes pg_dumpall or other routine maintenance operations. (CVE-2016-5424)

- Fix corner-case misbehaviors for `IS NULL`/`IS NOT NULL` applied to nested composite values (Andrew Gierth, Tom Lane)

  The SQL standard specifies that `IS NULL` should return TRUE for a row of all null values (thus `ROW(NULL,NULL) IS NULL` yields TRUE), but this is not meant to apply recursively (thus `ROW(NULL, ROW(NULL,NULL)) IS NULL` yields FALSE). The core executor got this right, but certain planner optimizations treated the test as recursive (thus producing TRUE in both cases), and `contrib/postgres_fdw` could produce remote queries that misbehaved similarly.

- Make the `inet` and `cidr` data types properly reject IPv6 addresses with too many colon-separated fields (Tom Lane)

- Prevent crash in `close_ps()` (the `point` `##` `lseg` operator) for NaN input coordinates (Tom Lane)

  Make it return NULL instead of crashing.

- Fix several one-byte buffer over-reads in `to_number()` (Peter Eisentraut)

  In several cases the `to_number()` function would read one more character than it should from the input string. There is a small chance of a crash, if the input happens to be adjacent to the end of memory.

- Avoid unsafe intermediate state during expensive paths through `heap_update()` (Masahiko Sawada, Andres Freund)

  Previously, these cases locked the target tuple (by setting its XMAX) but did not WAL-log that action, thus risking data integrity problems if the page were spilled to disk and then a database crash occurred before the tuple update could be completed.

- Avoid consuming a transaction ID during `VACUUM` (Alexander Korotkov)

  Some cases in `VACUUM` unnecessarily caused an XID to be assigned to the current transaction. Normally this is negligible, but if one is up against the XID wraparound limit, consuming more XIDs during anti-wraparound vacuums is a very bad thing.

- Avoid canceling hot-standby queries during `VACUUM FREEZE` (Simon Riggs, Álvaro Herrera)

  `VACUUM FREEZE` on an otherwise-idle master server could result in unnecessary cancellations of queries on its standby servers.

- When a manual `ANALYZE` specifies a column list, don't reset the table's `changes_since_analyze` counter (Tom Lane)

  If we're only analyzing some columns, we should not prevent routine auto-analyze from happening for the other columns.

- Fix `ANALYZE`'s overestimation of `n_distinct` for a unique or nearly-unique column with many null entries (Tom Lane)

  The nulls could get counted as though they were themselves distinct values, leading to serious planner misestimates in some types of queries.

- Prevent autovacuum from starting multiple workers for the same shared catalog (Álvaro Herrera)

  Normally this isn't much of a problem because the vacuum doesn't take long anyway; but in the case of a severely bloated catalog, it could result in all but one worker uselessly waiting instead of doing useful work on other tables.

- Fix `contrib/btree_gin` to handle the smallest possible `bigint` value correctly (Peter Eisentraut)

- Teach libpq to correctly decode server version from future servers (Peter Eisentraut)

  It's planned to switch to two-part instead of three-part server version numbers for releases after 9.6. Make sure that `PQserverVersion()` returns the correct value for such cases.

- Fix ecpg's code for `unsigned long long` array elements (Michael Meskes)

- Make pg_basebackup accept `-Z 0` as specifying no compression (Fujii Masao)

- Revert to the old heuristic timeout for `pg_ctl start -w` (Tom Lane)

  The new method adopted as of release 9.1.20 does not work when `silent_mode` is enabled, so go back to the old way.

- Fix makefiles' rule for building AIX shared libraries to be safe for parallel make (Noah Misch)

- Fix TAP tests and MSVC scripts to work when build directory's path name contains spaces (Michael Paquier, Kyotaro Horiguchi)

- Make regression tests safe for Danish and Welsh locales (Jeff Janes, Tom Lane)

  Change some test data that triggered the unusual sorting rules of these locales.

- Update our copy of the timezone code to match IANA's tzcode release 2016c (Tom Lane)

  This is needed to cope with anticipated future changes in the time zone data files. It also fixes some corner-case bugs in coping with unusual time zones.

- Update time zone data files to tzdata release 2016f for DST law changes in Kemerovo and Novosibirsk, plus historical corrections for Azerbaijan, Belarus, and Morocco.

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