E.34. Release 9.4.18
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## E.34. Release 9.4.18

Release date: 2018-05-10

This release contains a variety of fixes from 9.4.17. For information about new features in the 9.4 major release, see Section E.52.

### E.34.1. Migration to Version 9.4.18

A dump/restore is not required for those running 9.4.X.

However, if the function marking mistakes mentioned in the first changelog entry below affect you, you will want to take steps to correct your database catalogs.

Also, if you are upgrading from a version earlier than 9.4.17, see Section E.35.

### E.34.2. Changes

- Fix incorrect volatility markings on a few built-in functions (Thomas Munro, Tom Lane)

  The functions `query_to_xml`, `cursor_to_xml`, `cursor_to_xmlschema`, `query_to_xmlschema`, and `query_to_xml_and_xmlschema` should be marked volatile because they execute user-supplied queries that might contain volatile operations. They were not, leading to a risk of incorrect query optimization. This has been repaired for new installations by correcting the initial catalog data, but existing installations will continue to contain the incorrect markings. Practical use of these functions seems to pose little hazard, but in case of trouble, it can be fixed by manually updating these functions' `pg_proc` entries, for example `ALTER FUNCTION pg_catalog.query_to_xml(text, boolean, boolean, text) VOLATILE`. (Note that that will need to be done in each database of the installation.) Another option is to pg_upgrade the database to a version containing the corrected initial data.

- Avoid re-using TOAST value OIDs that match dead-but-not-yet-vacuumed TOAST entries (Pavan Deolasee)

  Once the OID counter has wrapped around, it's possible to assign a TOAST value whose OID matches a previously deleted entry in the same TOAST table. If that entry were not yet vacuumed away, this resulted in “unexpected chunk number 0 (expected 1) for toast value `nnnnn`” errors, which would persist until the dead entry was removed by `VACUUM`. Fix by not selecting such OIDs when creating a new TOAST entry.

- Change `ANALYZE`'s algorithm for updating `pg_class`.`reltuples` (David Gould)

  Previously, pages not actually scanned by `ANALYZE` were assumed to retain their old tuple density. In a large table where `ANALYZE` samples only a small fraction of the pages, this meant that the overall tuple density estimate could not change very much, so that `reltuples` would change nearly proportionally to changes in the table's physical size (`relpages`) regardless of what was actually happening in the table. This has been observed to result in `reltuples` becoming so much larger than reality as to effectively shut off autovacuuming. To fix, assume that `ANALYZE`'s sample is a statistically unbiased sample of the table (as it should be), and just extrapolate the density observed within those pages to the whole table.

- Avoid deadlocks in concurrent `CREATE INDEX CONCURRENTLY` commands that are run under `SERIALIZABLE` or `REPEATABLE READ` transaction isolation (Tom Lane)

- Fix possible slow execution of `REFRESH MATERIALIZED VIEW CONCURRENTLY` (Thomas Munro)

- Fix `UPDATE/DELETE ... WHERE CURRENT OF` to not fail when the referenced cursor uses an index-only-scan plan (Yugo Nagata, Tom Lane)

- Fix incorrect planning of join clauses pushed into parameterized paths (Andrew Gierth, Tom Lane)

  This error could result in misclassifying a condition as a “join filter” for an outer join when it should be a plain “filter” condition, leading to incorrect join output.

- Fix misoptimization of `CHECK` constraints having provably-NULL subclauses of top-level `AND`/`OR` conditions (Tom Lane, Dean Rasheed)

  This could, for example, allow constraint exclusion to exclude a child table that should not be excluded from a query.

- Avoid failure if a query-cancel or session-termination interrupt occurs while committing a prepared transaction (Stas Kelvich)

- Fix query-lifespan memory leakage in repeatedly executed hash joins (Tom Lane)

- Fix overly strict sanity check in `heap_prepare_freeze_tuple` (Álvaro Herrera)

  This could result in incorrect “cannot freeze committed xmax” failures in databases that have been pg_upgrade'd from 9.2 or earlier.

- Prevent dangling-pointer dereference when a C-coded before-update row trigger returns the “old” tuple (Rushabh Lathia)

- Reduce locking during autovacuum worker scheduling (Jeff Janes)

  The previous behavior caused drastic loss of potential worker concurrency in databases with many tables.

- Ensure client hostname is copied while copying `pg_stat_activity` data to local memory (Edmund Horner)

  Previously the supposedly-local snapshot contained a pointer into shared memory, allowing the client hostname column to change unexpectedly if any existing session disconnected.

- Fix incorrect processing of multiple compound affixes in `ispell` dictionaries (Arthur Zakirov)

- Fix collation-aware searches (that is, indexscans using inequality operators) in SP-GiST indexes on text columns (Tom Lane)

  Such searches would return the wrong set of rows in most non-C locales.

- Count the number of index tuples correctly during initial build of an SP-GiST index (Tomas Vondra)

  Previously, the tuple count was reported to be the same as that of the underlying table, which is wrong if the index is partial.

- Count the number of index tuples correctly during vacuuming of a GiST index (Andrey Borodin)

  Previously it reported the estimated number of heap tuples, which might be inaccurate, and is certainly wrong if the index is partial.

- Fix a corner case where a streaming standby gets stuck at a WAL continuation record (Kyotaro Horiguchi)

- In logical decoding, avoid possible double processing of WAL data when a walsender restarts (Craig Ringer)

- Allow `scalarltsel` and `scalargtsel` to be used on non-core datatypes (Tomas Vondra)

- Reduce libpq's memory consumption when a server error is reported after a large amount of query output has been collected (Tom Lane)

  Discard the previous output before, not after, processing the error message. On some platforms, notably Linux, this can make a difference in the application's subsequent memory footprint.

- Fix double-free crashes in ecpg (Patrick Krecker, Jeevan Ladhe)

- Fix ecpg to handle `long long int` variables correctly in MSVC builds (Michael Meskes, Andrew Gierth)

- Fix mis-quoting of values for list-valued GUC variables in dumps (Michael Paquier, Tom Lane)

  The `local_preload_libraries`, `session_preload_libraries`, `shared_preload_libraries`, and `temp_tablespaces` variables were not correctly quoted in pg_dump output. This would cause problems if settings for these variables appeared in `CREATE FUNCTION ... SET` or `ALTER DATABASE/ROLE ... SET` clauses.

- Fix pg_recvlogical to not fail against pre-v10 PostgreSQL servers (Michael Paquier)

  A previous fix caused pg_recvlogical to issue a command regardless of server version, but it should only be issued to v10 and later servers.

- Fix overflow handling in PL/pgSQL integer `FOR` loops (Tom Lane)

  The previous coding failed to detect overflow of the loop variable on some non-gcc compilers, leading to an infinite loop.

- Adjust PL/Python regression tests to pass under Python 3.7 (Peter Eisentraut)

- Support testing PL/Python and related modules when building with Python 3 and MSVC (Andrew Dunstan)

- Rename internal `b64_encode` and `b64_decode` functions to avoid conflict with Solaris 11.4 built-in functions (Rainer Orth)

- Sync our copy of the timezone library with IANA tzcode release 2018e (Tom Lane)

  This fixes the zic timezone data compiler to cope with negative daylight-savings offsets. While the PostgreSQL project will not immediately ship such timezone data, zic might be used with timezone data obtained directly from IANA, so it seems prudent to update zic now.

- Update time zone data files to tzdata release 2018d for DST law changes in Palestine and Antarctica (Casey Station), plus historical corrections for Portugal and its colonies, as well as Enderbury, Jamaica, Turks & Caicos Islands, and Uruguay.

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