PostgreSQL 9.6.2 Documentation
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# E.89. Release 9.0.20

> Release Date: 2015-05-22

This release contains a variety of fixes from 9.0.19. For information about new features in the 9.0 major release, see Section E.109.

The PostgreSQL community will stop releasing updates for the 9.0.X release series in September 2015. Users are encouraged to update to a newer release branch soon.

## E.89.1. Migration to Version 9.0.20

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

However, if you are upgrading from a version earlier than 9.0.18, see Section E.91.

## E.89.2. Changes

- Avoid possible crash when client disconnects just before the authentication timeout expires (Benkocs Norbert Attila)

  If the timeout interrupt fired partway through the session shutdown sequence, SSL-related state would be freed twice, typically causing a crash and hence denial of service to other sessions. Experimentation shows that an unauthenticated remote attacker could trigger the bug somewhat consistently, hence treat as security issue. (CVE-2015-3165)

- Improve detection of system-call failures (Noah Misch)

  Our replacement implementation of `snprintf()` failed to check for errors reported by the underlying system library calls; the main case that might be missed is out-of-memory situations. In the worst case this might lead to information exposure, due to our code assuming that a buffer had been overwritten when it hadn't been. Also, there were a few places in which security-relevant calls of other system library functions did not check for failure.

  It remains possible that some calls of the `*printf()` family of functions are vulnerable to information disclosure if an out-of-memory error occurs at just the wrong time. We judge the risk to not be large, but will continue analysis in this area. (CVE-2015-3166)

- In `contrib/pgcrypto`, uniformly report decryption failures as "Wrong key or corrupt data" (Noah Misch)

  Previously, some cases of decryption with an incorrect key could report other error message texts. It has been shown that such variance in error reports can aid attackers in recovering keys from other systems. While it's unknown whether `pgcrypto`'s specific behaviors are likewise exploitable, it seems better to avoid the risk by using a one-size-fits-all message. (CVE-2015-3167)

- Fix incorrect checking of deferred exclusion constraints after a HOT update (Tom Lane)

  If a new row that potentially violates a deferred exclusion constraint is HOT-updated (that is, no indexed columns change and the row can be stored back onto the same table page) later in the same transaction, the exclusion constraint would be reported as violated when the check finally occurred, even if the row(s) the new row originally conflicted with had been deleted.

- Prevent improper reordering of antijoins (NOT EXISTS joins) versus other outer joins (Tom Lane)

  This oversight in the planner has been observed to cause "could not find RelOptInfo for given relids" errors, but it seems possible that sometimes an incorrect query plan might get past that consistency check and result in silently-wrong query output.

- Fix incorrect matching of subexpressions in outer-join plan nodes (Tom Lane)

  Previously, if textually identical non-strict subexpressions were used both above and below an outer join, the planner might try to re-use the value computed below the join, which would be incorrect because the executor would force the value to NULL in case of an unmatched outer row.

- Fix GEQO planner to cope with failure of its join order heuristic (Tom Lane)

  This oversight has been seen to lead to "failed to join all relations together" errors in queries involving `LATERAL`, and that might happen in other cases as well.

- Fix possible deadlock at startup when `max_prepared_transactions` is too small (Heikki Linnakangas)

- Don't archive useless preallocated WAL files after a timeline switch (Heikki Linnakangas)

- Avoid "cannot GetMultiXactIdMembers() during recovery" error (Álvaro Herrera)

- Recursively `fsync()` the data directory after a crash (Abhijit Menon-Sen, Robert Haas)

  This ensures consistency if another crash occurs shortly later. (The second crash would have to be a system-level crash, not just a database crash, for there to be a problem.)

- Fix autovacuum launcher's possible failure to shut down, if an error occurs after it receives SIGTERM (Álvaro Herrera)

- Cope with unexpected signals in `LockBufferForCleanup()` (Andres Freund)

  This oversight could result in spurious errors about "multiple backends attempting to wait for pincount 1".

- Avoid waiting for WAL flush or synchronous replication during commit of a transaction that was read-only so far as the user is concerned (Andres Freund)

  Previously, a delay could occur at commit in transactions that had written WAL due to HOT page pruning, leading to undesirable effects such as sessions getting stuck at startup if all synchronous replicas are down. Sessions have also been observed to get stuck in catchup interrupt processing when using synchronous replication; this will fix that problem as well.

- Fix crash when manipulating hash indexes on temporary tables (Heikki Linnakangas)

- Fix possible failure during hash index bucket split, if other processes are modifying the index concurrently (Tom Lane)

- Check for interrupts while analyzing index expressions (Jeff Janes)

  `ANALYZE` executes index expressions many times; if there are slow functions in such an expression, it's desirable to be able to cancel the `ANALYZE` before that loop finishes.

- Add the name of the target server to object description strings for foreign-server user mappings (Álvaro Herrera)

- Recommend setting `include_realm` to 1 when using Kerberos/GSSAPI/SSPI authentication (Stephen Frost)

  Without this, identically-named users from different realms cannot be distinguished. For the moment this is only a documentation change, but it will become the default setting in PostgreSQL 9.5.

- Remove code for matching IPv4 `pg_hba.conf` entries to IPv4-in-IPv6 addresses (Tom Lane)

  This hack was added in 2003 in response to a report that some Linux kernels of the time would report IPv4 connections as having IPv4-in-IPv6 addresses. However, the logic was accidentally broken in 9.0. The lack of any field complaints since then shows that it's not needed anymore. Now we have reports that the broken code causes crashes on some systems, so let's just remove it rather than fix it. (Had we chosen to fix it, that would make for a subtle and potentially security-sensitive change in the effective meaning of IPv4 `pg_hba.conf` entries, which does not seem like a good thing to do in minor releases.)

- While shutting down service on Windows, periodically send status updates to the Service Control Manager to prevent it from killing the service too soon; and ensure that pg_ctl will wait for shutdown (Krystian Bigaj)

- Reduce risk of network deadlock when using libpq's non-blocking mode (Heikki Linnakangas)

  When sending large volumes of data, it's important to drain the input buffer every so often, in case the server has sent enough response data to cause it to block on output. (A typical scenario is that the server is sending a stream of NOTICE messages during `COPY FROM STDIN`.) This worked properly in the normal blocking mode, but not so much in non-blocking mode. We've modified libpq to opportunistically drain input when it can, but a full defense against this problem requires application cooperation: the application should watch for socket read-ready as well as write-ready conditions, and be sure to call `PQconsumeInput()` upon read-ready.

- Fix array handling in ecpg (Michael Meskes)

- Fix psql to sanely handle URIs and conninfo strings as the first parameter to `\connect` (David Fetter, Andrew Dunstan, Álvaro Herrera)

  This syntax has been accepted (but undocumented) for a long time, but previously some parameters might be taken from the old connection instead of the given string, which was agreed to be undesirable.

- Suppress incorrect complaints from psql on some platforms that it failed to write `~/.psql_history` at exit (Tom Lane)

  This misbehavior was caused by a workaround for a bug in very old (pre-2006) versions of libedit. We fixed it by removing the workaround, which will cause a similar failure to appear for anyone still using such versions of libedit. Recommendation: upgrade that library, or use libreadline.

- Fix pg_dump's rule for deciding which casts are system-provided casts that should not be dumped (Tom Lane)

- Fix dumping of views that are just `VALUES(...)` but have column aliases (Tom Lane)

- In pg_upgrade, force timeline 1 in the new cluster (Bruce Momjian)

  This change prevents upgrade failures caused by bogus complaints about missing WAL history files.

- In pg_upgrade, check for improperly non-connectable databases before proceeding (Bruce Momjian)

- In pg_upgrade, quote directory paths properly in the generated `delete_old_cluster` script (Bruce Momjian)

- In pg_upgrade, preserve database-level freezing info properly (Bruce Momjian)

  This oversight could cause missing-clog-file errors for tables within the `postgres` and `template1` databases.

- Run pg_upgrade and pg_resetxlog with restricted privileges on Windows, so that they don't fail when run by an administrator (Muhammad Asif Naeem)

- Fix slow sorting algorithm in `contrib/intarray` (Tom Lane)

- Fix compile failure on Sparc V8 machines (Rob Rowan)

- Update time zone data files to tzdata release 2015d for DST law changes in Egypt, Mongolia, and Palestine, plus historical changes in Canada and Chile. Also adopt revised zone abbreviations for the America/Adak zone (HST/HDT not HAST/HADT).

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