## E.16. Release 11

Release date: 2018-10-18

### E.16.1. Overview

Major enhancements in PostgreSQL 11 include:

- Improvements to partitioning functionality, including:

  - Add support for partitioning by a hash key

  - Add support for `PRIMARY KEY`, `FOREIGN KEY`, indexes, and triggers on partitioned tables

  - Allow creation of a “default” partition for storing data that does not match any of the remaining partitions

  - `UPDATE` statements that change a partition key column now cause affected rows to be moved to the appropriate partitions

  - Improve `SELECT` performance through enhanced partition elimination strategies during query planning and execution

- Improvements to parallelism, including:

  - `CREATE INDEX` can now use parallel processing while building a B-tree index

  - Parallelization is now possible in `CREATE TABLE ... AS`, `CREATE MATERIALIZED VIEW`, and certain queries using `UNION`

  - Parallelized hash joins and parallelized sequential scans now perform better

- SQL stored procedures that support embedded transactions

- Optional Just-in-Time (JIT) compilation for some SQL code, speeding evaluation of expressions

- Window functions now support all framing options shown in the SQL:2011 standard, including `RANGE `distance` PRECEDING/FOLLOWING`, `GROUPS` mode, and frame exclusion options

- Covering indexes can now be created, using the `INCLUDE` clause of `CREATE INDEX`

- Many other useful performance improvements, including the ability to avoid a table rewrite for `ALTER TABLE ... ADD COLUMN` with a non-null column default

The above items are explained in more detail in the sections below.

### E.16.2. Migration to Version 11

A dump/restore using pg_dumpall or use of pg_upgrade or logical replication is required for those wishing to migrate data from any previous release. See Section 17.6 for general information on migrating to new major releases.

Version 11 contains a number of changes that may affect compatibility with previous releases. Observe the following incompatibilities:

- Make pg_dump dump the properties of a database, not just its contents (Haribabu Kommi)

  Previously, attributes of the database itself, such as database-level `GRANT`/`REVOKE` permissions and `ALTER DATABASE SET` variable settings, were only dumped by pg_dumpall. Now `pg_dump --create` and `pg_restore --create` will restore these database properties in addition to the objects within the database. `pg_dumpall -g` now only dumps role- and tablespace-related attributes. pg_dumpall's complete output (without `-g`) is unchanged.

  pg_dump and pg_restore, without `--create`, no longer dump/restore database-level comments and security labels; those are now treated as properties of the database.

  pg_dumpall's output script will now always create databases with their original locale and encoding, and hence will fail if the locale or encoding name is unknown to the destination system. Previously, `CREATE DATABASE` would be emitted without these specifications if the database locale and encoding matched the old cluster's defaults.

  `pg_dumpall --clean` now restores the original locale and encoding settings of the `postgres` and `template1` databases, as well as those of user-created databases.

- Consider syntactic form when disambiguating function versus column references (Tom Lane)

  When `x` is a table name or composite column, PostgreSQL has traditionally considered the syntactic forms ``f`(`x`)` and ``x`.`f`` to be equivalent, allowing tricks such as writing a function and then using it as though it were a computed-on-demand column. However, if both interpretations are feasible, the column interpretation was always chosen, leading to surprising results if the user intended the function interpretation. Now, if there is ambiguity, the interpretation that matches the syntactic form is chosen.

- Fully enforce uniqueness of table and domain constraint names (Tom Lane)

  PostgreSQL expects the names of a table's constraints to be distinct, and likewise for the names of a domain's constraints. However, there was not rigid enforcement of this, and previously there were corner cases where duplicate names could be created.

- Make `power(numeric, numeric)` and `power(float8, float8)` handle `NaN` inputs according to the POSIX standard (Tom Lane, Dang Minh Huong)

  POSIX says that `NaN ^ 0 = 1` and `1 ^ NaN = 1`, but all other cases with `NaN` input(s) should return `NaN`. `power(numeric, numeric)` just returned `NaN` in all such cases; now it honors the two exceptions. `power(float8, float8)` followed the standard if the C library does; but on some old Unix platforms the library doesn't, and there were also problems on some versions of Windows.

- Prevent `to_number()` from consuming characters when the template separator does not match (Oliver Ford)

  Specifically, `SELECT to_number('1234', '9,999')` used to return `134`. It will now return `1234`. `L` and `TH` now only consume characters that are not digits, positive/negative signs, decimal points, or commas.

- Fix `to_date()`, `to_number()`, and `to_timestamp()` to skip a character for each template character (Tom Lane)

  Previously, they skipped one byte for each byte of template character, resulting in strange behavior if either string contained multibyte characters.

- Adjust the handling of backslashes inside double-quotes in template strings for `to_char()`, `to_number()`, and `to_timestamp()`.

  Such a backslash now escapes the character after it, particularly a double-quote or another backslash.

- Correctly handle relative path expressions in `xmltable()`, `xpath()`, and other XML-handling functions (Markus Winand)

  Per the SQL standard, relative paths start from the document node of the XML input document, not the root node as these functions previously did.

- In the extended query protocol, make `statement_timeout` apply to each Execute message separately, not to all commands before Sync (Tatsuo Ishii, Andres Freund)

- Remove the `relhaspkey` column from system catalog `pg_class` (Peter Eisentraut)

  Applications needing to check for a primary key should consult `pg_index`.

- Replace system catalog `pg_proc`'s `proisagg` and `proiswindow` columns with `prokind` (Peter Eisentraut)

  This new column more clearly distinguishes functions, procedures, aggregates, and window functions.

- Correct information schema column `tables`.`table_type` to return `FOREIGN` instead of `FOREIGN TABLE` (Peter Eisentraut)

  This new output matches the SQL standard.

- Change the ps process display labels for background workers to match the `pg_stat_activity`.`backend_type` labels (Peter Eisentraut)

- Cause large object permission checks to happen during large object open, `lo_open()`, not when a read or write is attempted (Tom Lane, Michael Paquier)

  If write access is requested and not available, an error will now be thrown even if the large object is never written to.

- Prevent non-superusers from reindexing shared catalogs (Michael Paquier, Robert Haas)

  Previously, database owners were also allowed to do this, but now it is considered outside the bounds of their privileges.

- Remove deprecated `adminpack` functions `pg_file_read()`, `pg_file_length()`, and `pg_logfile_rotate()` (Stephen Frost)

  Equivalent functionality is now present in the core backend. Existing `adminpack` installs will continue to have access to these functions until they are updated via `ALTER EXTENSION ... UPDATE`.

- Honor the capitalization of double-quoted command options (Daniel Gustafsson)

  Previously, option names in certain SQL commands were forcibly lower-cased even if entered with double quotes; thus for example `"FillFactor"` would be accepted as an index storage option, though properly its name is lower-case. Such cases will now generate an error.

- Remove server parameter `replacement_sort_tuples` (Peter Geoghegan)

  Replacement sorts were determined to be no longer useful.

- Remove `WITH` clause in `CREATE FUNCTION` (Michael Paquier)

  PostgreSQL has long supported a more standard-compliant syntax for this capability.

- In PL/pgSQL trigger functions, the `OLD` and `NEW` variables now read as NULL when not assigned (Tom Lane)

  Previously, references to these variables could be parsed but not executed.

### E.16.3. Changes

Below you will find a detailed account of the changes between PostgreSQL 11 and the previous major release.

#### E.16.3.1. Server

##### E.16.3.1.1. Partitioning

- Allow the creation of partitions based on hashing a key column (Amul Sul)

- Support indexes on partitioned tables (Álvaro Herrera, Amit Langote)

  An “index” on a partitioned table is not a physical index across the whole partitioned table, but rather a template for automatically creating similar indexes on each partition of the table.

  If the partition key is part of the index's column set, a partitioned index may be declared `UNIQUE`. It will represent a valid uniqueness constraint across the whole partitioned table, even though each physical index only enforces uniqueness within its own partition.

  The new command `ALTER INDEX ATTACH PARTITION` causes an existing index on a partition to be associated with a matching index template for its partitioned table. This provides flexibility in setting up a new partitioned index for an existing partitioned table.

- Allow foreign keys on partitioned tables (Álvaro Herrera)

- Allow `FOR EACH ROW` triggers on partitioned tables (Álvaro Herrera)

  Creation of a trigger on a partitioned table automatically creates triggers on all existing and future partitions. This also allows deferred unique constraints on partitioned tables.

- Allow partitioned tables to have a default partition (Jeevan Ladhe, Beena Emerson, Ashutosh Bapat, Rahila Syed, Robert Haas)

  The default partition will store rows that don't match any of the other defined partitions, and is searched accordingly.

- `UPDATE` statements that change a partition key column now cause affected rows to be moved to the appropriate partitions (Amit Khandekar)

- Allow `INSERT`, `UPDATE`, and `COPY` on partitioned tables to properly route rows to foreign partitions (Etsuro Fujita, Amit Langote)

  This is supported by `postgres_fdw` foreign tables. Since the `ExecForeignInsert` callback function is called for this in a different way than it used to be, foreign data wrappers must be modified to cope with this change.

- Allow faster partition elimination during query processing (Amit Langote, David Rowley, Dilip Kumar)

  This speeds access to partitioned tables with many partitions.

- Allow partition elimination during query execution (David Rowley, Beena Emerson)

  Previously, partition elimination only happened at planning time, meaning many joins and prepared queries could not use partition elimination.

- In an equality join between partitioned tables, allow matching partitions to be joined directly (Ashutosh Bapat)

  This feature is disabled by default but can be enabled by changing `enable_partitionwise_join`.

- Allow aggregate functions on partitioned tables to be evaluated separately for each partition, subsequently merging the results (Jeevan Chalke, Ashutosh Bapat, Robert Haas)

  This feature is disabled by default but can be enabled by changing `enable_partitionwise_aggregate`.

- Allow `postgres_fdw` to push down aggregates to foreign tables that are partitions (Jeevan Chalke)

##### E.16.3.1.2. Parallel Queries

- Allow parallel building of a btree index (Peter Geoghegan, Rushabh Lathia, Heikki Linnakangas)

- Allow hash joins to be performed in parallel using a shared hash table (Thomas Munro)

- Allow `UNION` to run each `SELECT` in parallel if the individual `SELECT`s cannot be parallelized (Amit Khandekar, Robert Haas, Amul Sul)

- Allow partition scans to more efficiently use parallel workers (Amit Khandekar, Robert Haas, Amul Sul)

- Allow `LIMIT` to be passed to parallel workers (Robert Haas, Tom Lane)

  This allows workers to reduce returned results and use targeted index scans.

- Allow single-evaluation queries, e.g. `WHERE` clause aggregate queries, and functions in the target list to be parallelized (Amit Kapila, Robert Haas)

- Add server parameter `parallel_leader_participation` to control whether the leader also executes subplans (Thomas Munro)

  The default is enabled, meaning the leader will execute subplans.

- Allow parallelization of commands `CREATE TABLE ... AS`, `SELECT INTO`, and `CREATE MATERIALIZED VIEW` (Haribabu Kommi)

- Improve performance of sequential scans with many parallel workers (David Rowley)

- Add reporting of parallel workers' sort activity in `EXPLAIN` (Robert Haas, Tom Lane)

##### E.16.3.1.3. Indexes

- Allow B-tree indexes to include columns that are not part of the search key or unique constraint, but are available to be read by index-only scans (Anastasia Lubennikova, Alexander Korotkov, Teodor Sigaev)

  This is enabled by the new `INCLUDE` clause of `CREATE INDEX`. It facilitates building “covering indexes” that optimize specific types of queries. Columns can be included even if their data types don't have B-tree support.

- Improve performance of monotonically increasing index additions (Pavan Deolasee, Peter Geoghegan)

- Improve performance of hash index scans (Ashutosh Sharma)

- Add predicate locking for hash, GiST and GIN indexes (Shubham Barai)

  This reduces the likelihood of serialization conflicts in serializable-mode transactions.

###### E.16.3.1.3.1. SP-Gist

- Add prefix-match operator `text` `^@` `text`, which is supported by SP-GiST (Ildus Kurbangaliev)

  This is similar to using `var` `LIKE 'word%'` with a btree index, but it is more efficient.

- Allow polygons to be indexed with SP-GiST (Nikita Glukhov, Alexander Korotkov)

- Allow SP-GiST to use lossy representation of leaf keys (Teodor Sigaev, Heikki Linnakangas, Alexander Korotkov, Nikita Glukhov)

##### E.16.3.1.4. Optimizer

- Improve selection of the most common values for statistics (Jeff Janes, Dean Rasheed)

  Previously, the most common values (MCVs) were identified based on their frequency compared to all column values. Now, MCVs are chosen based on their frequency compared to the non-MCV values. This improves the robustness of the algorithm for both uniform and non-uniform distributions.

- Improve selectivity estimates for `>=` and `<=` (Tom Lane)

  Previously, such cases used the same selectivity estimates as `>` and `<`, respectively, unless the comparison constants are MCVs. This change is particularly helpful for queries involving `BETWEEN` with small ranges.

- Reduce `var` `=` `var` to `var` `IS NOT NULL` where equivalent (Tom Lane)

  This leads to better selectivity estimates.

- Improve optimizer's row count estimates for `EXISTS` and `NOT EXISTS` queries (Tom Lane)

- Make the optimizer account for evaluation costs and selectivity of `HAVING` clauses (Tom Lane)

##### E.16.3.1.5. General Performance

- Add Just-in-Time (JIT) compilation of some parts of query plans to improve execution speed (Andres Freund)

  This feature requires LLVM to be available. It is not currently enabled by default, even in builds that support it.

- Allow bitmap scans to perform index-only scans when possible (Alexander Kuzmenkov)

- Update the free space map during `VACUUM` (Claudio Freire)

  This allows free space to be reused more quickly.

- Allow `VACUUM` to avoid unnecessary index scans (Masahiko Sawada, Alexander Korotkov)

- Improve performance of committing multiple concurrent transactions (Amit Kapila)

- Reduce memory usage for queries using set-returning functions in their target lists (Andres Freund)

- Improve the speed of aggregate computations (Andres Freund)

- Allow `postgres_fdw` to push `UPDATE`s and `DELETE`s using joins to foreign servers (Etsuro Fujita)

  Previously, only non-join `UPDATE`s and `DELETE`s were pushed.

- Add support for large pages on Windows (Takayuki Tsunakawa, Thomas Munro)

  This is controlled by the huge_pages configuration parameter.

##### E.16.3.1.6. Monitoring

- Show memory usage in output from `log_statement_stats`, `log_parser_stats`, `log_planner_stats`, and `log_executor_stats` (Justin Pryzby, Peter Eisentraut)

- Add column `pg_stat_activity`.`backend_type` to show the type of a background worker (Peter Eisentraut)

  The type is also visible in ps output.

- Make `log_autovacuum_min_duration` log skipped tables that are concurrently being dropped (Nathan Bossart)

###### E.16.3.1.6.1. Information Schema

- Add `information_schema` columns related to table constraints and triggers (Peter Eisentraut)

  Specifically, `triggers`.`action_order`, `triggers`.`action_reference_old_table`, and `triggers`.`action_reference_new_table` are now populated, where before they were always null. Also, `table_constraints`.`enforced` now exists but is not yet usefully populated.

##### E.16.3.1.7. Authentication

- Allow the server to specify more complex LDAP specifications in search+bind mode (Thomas Munro)

  Specifically, `ldapsearchfilter` allows pattern matching using combinations of LDAP attributes.

- Allow LDAP authentication to use encrypted LDAP (Thomas Munro)

  We already supported LDAP over TLS by using `ldaptls=1`. This new TLS LDAP method for encrypted LDAP is enabled with `ldapscheme=ldaps` or `ldapurl=ldaps://`.

- Improve logging of LDAP errors (Thomas Munro)

##### E.16.3.1.8. Permissions

- Add default roles that enable file system access (Stephen Frost)

  Specifically, the new roles are: `pg_read_server_files`, `pg_write_server_files`, and `pg_execute_server_program`. These roles now also control who can use server-side `COPY` and the `file_fdw` extension. Previously, only superusers could use these functions, and that is still the default behavior.

- Allow access to file system functions to be controlled by `GRANT`/`REVOKE` permissions, rather than superuser checks (Stephen Frost)

  Specifically, these functions were modified: `pg_ls_dir()`, `pg_read_file()`, `pg_read_binary_file()`, `pg_stat_file()`.

- Use `GRANT`/`REVOKE` to control access to `lo_import()` and `lo_export()` (Michael Paquier, Tom Lane)

  Previously, only superusers were granted access to these functions.

  The compile-time option `ALLOW_DANGEROUS_LO_FUNCTIONS` has been removed.

- Use view owner not session owner when preventing non-password access to `postgres_fdw` tables (Robert Haas)

  PostgreSQL only allows superusers to access `postgres_fdw` tables without passwords, e.g. via `peer`. Previously, the session owner had to be a superuser to allow such access; now the view owner is checked instead.

- Fix invalid locking permission check in `SELECT FOR UPDATE` on views (Tom Lane)

##### E.16.3.1.9. Server Configuration

- Add server setting `ssl_passphrase_command` to allow supplying of the passphrase for SSL key files (Peter Eisentraut)

  Also add `ssl_passphrase_command_supports_reload` to specify whether the SSL configuration should be reloaded and `ssl_passphrase_command` called during a server configuration reload.

- Add storage parameter `toast_tuple_target` to control the minimum tuple length before TOAST storage will be considered (Simon Riggs)

  The default TOAST threshold has not been changed.

- Allow server options related to memory and file sizes to be specified in units of bytes (Beena Emerson)

  The new unit suffix is “B”. This is in addition to the existing units “kB”, “MB”, “GB” and “TB”.

##### E.16.3.1.10. Write-Ahead Log (WAL)

- Allow the WAL file size to be set during initdb (Beena Emerson)

  Previously, the 16MB default could only be changed at compile time.

- Retain WAL data for only a single checkpoint (Simon Riggs)

  Previously, WAL was retained for two checkpoints.

- Fill the unused portion of force-switched WAL segment files with zeros for improved compressibility (Chapman Flack)

#### E.16.3.2. Base Backup and Streaming Replication

- Replicate `TRUNCATE` activity when using logical replication (Simon Riggs, Marco Nenciarini, Peter Eisentraut)

- Pass prepared transaction information to logical replication subscribers (Nikhil Sontakke, Stas Kelvich)

- Exclude unlogged tables, temporary tables, and `pg_internal.init` files from streaming base backups (David Steele)

  There is no need to copy such files.

- Allow checksums of heap pages to be verified during streaming base backup (Michael Banck)

- Allow replication slots to be advanced programmatically, rather than be consumed by subscribers (Petr Jelinek)

  This allows efficient advancement of replication slots when the contents do not need to be consumed. This is performed by `pg_replication_slot_advance()`.

- Add timeline information to the `backup_label` file (Michael Paquier)

  Also add a check that the WAL timeline matches the `backup_label` file's timeline.

- Add host and port connection information to the `pg_stat_wal_receiver` system view (Haribabu Kommi)

#### E.16.3.3. Utility Commands

- Allow `ALTER TABLE` to add a column with a non-null default without doing a table rewrite (Andrew Dunstan, Serge Rielau)

  This is enabled when the default value is a constant.

- Allow views to be locked by locking the underlying tables (Yugo Nagata)

- Allow `ALTER INDEX` to set statistics-gathering targets for expression indexes (Alexander Korotkov, Adrien Nayrat)

  In psql, `\d+` now shows the statistics target for indexes.

- Allow multiple tables to be specified in one `VACUUM` or `ANALYZE` command (Nathan Bossart)

  Also, if any table mentioned in `VACUUM` uses a column list, then the `ANALYZE` keyword must be supplied; previously, `ANALYZE` was implied in such cases.

- Add parenthesized options syntax to `ANALYZE` (Nathan Bossart)

  This is similar to the syntax supported by `VACUUM`.

- Add `CREATE AGGREGATE` option to specify the behavior of the aggregate's finalization function (Tom Lane)

  This is helpful for allowing user-defined aggregate functions to be optimized and to work as window functions.

#### E.16.3.4. Data Types

- Allow the creation of arrays of domains (Tom Lane)

  This also allows `array_agg()` to be used on domains.

- Support domains over composite types (Tom Lane)

  Also allow PL/Perl, PL/Python, and PL/Tcl to handle composite-domain function arguments and results. Also improve PL/Python domain handling.

- Add casts from `JSONB` scalars to numeric and boolean data types (Anastasia Lubennikova)

#### E.16.3.5. Functions

- Add all window function framing options specified by SQL:2011 (Oliver Ford, Tom Lane)

  Specifically, allow `RANGE` mode to use `PRECEDING` and `FOLLOWING` to select rows having grouping values within plus or minus the specified offset. Add `GROUPS` mode to include plus or minus the number of peer groups. Frame exclusion syntax was also added.

- Add SHA-2 family of hash functions (Peter Eisentraut)

  Specifically, `sha224()`, `sha256()`, `sha384()`, `sha512()` were added.

- Add support for 64-bit non-cryptographic hash functions (Robert Haas, Amul Sul)

- Allow `to_char()` and `to_timestamp()` to specify the time zone's offset from UTC in hours and minutes (Nikita Glukhov, Andrew Dunstan)

  This is done with format specifications `TZH` and `TZM`.

- Add text search function `websearch_to_tsquery()` that supports a query syntax similar to that used by web search engines (Victor Drobny, Dmitry Ivanov)

- Add functions `json(b)_to_tsvector()` to create a text search query for matching `JSON`/`JSONB` values (Dmitry Dolgov)

#### E.16.3.6. Server-Side Languages

- Add SQL-level procedures, which can start and commit their own transactions (Peter Eisentraut)

  They are created with the new `CREATE PROCEDURE` command and invoked via `CALL`.

  The new `ALTER`/`DROP ROUTINE` commands allow altering/dropping of all routine-like objects, including procedures, functions, and aggregates.

  Also, writing `FUNCTION` is now preferred over writing `PROCEDURE` in `CREATE OPERATOR` and `CREATE TRIGGER`, because the referenced object must be a function not a procedure. However, the old syntax is still accepted for compatibility.

- Add transaction control to PL/pgSQL, PL/Perl, PL/Python, PL/Tcl, and SPI server-side languages (Peter Eisentraut)

  Transaction control is only available within top-transaction-level procedures and nested `DO` and `CALL` blocks that only contain other `DO` and `CALL` blocks.

- Add the ability to define PL/pgSQL composite-type variables as not null, constant, or with initial values (Tom Lane)

- Allow PL/pgSQL to handle changes to composite types (e.g. record, row) that happen between the first and later function executions in the same session (Tom Lane)

  Previously, such circumstances generated errors.

- Add extension `jsonb_plpython` to transform `JSONB` to/from PL/Python types (Anthony Bykov)

- Add extension `jsonb_plperl` to transform `JSONB` to/from PL/Perl types (Anthony Bykov)

#### E.16.3.7. Client Interfaces

- Change libpq to disable compression by default (Peter Eisentraut)

  Compression is already disabled in modern OpenSSL versions, so that the libpq setting had no effect with such libraries.

- Add `DO CONTINUE` option to ecpg's `WHENEVER` statement (Vinayak Pokale)

  This generates a C `continue` statement, causing a return to the top of the contained loop when the specified condition occurs.

- Add an ecpg mode to enable Oracle Pro*C-style handling of char arrays.

  This mode is enabled with `-C`.

#### E.16.3.8. Client Applications

##### E.16.3.8.1. psql

- Add psql command `\gdesc` to display the names and types of the columns in a query result (Pavel Stehule)

- Add psql variables to report query activity and errors (Fabien Coelho)

  Specifically, the new variables are `ERROR`, `SQLSTATE`, `ROW_COUNT`, `LAST_ERROR_MESSAGE`, and `LAST_ERROR_SQLSTATE`.

- Allow psql to test for the existence of a variable (Fabien Coelho)

  Specifically, the syntax `:{?variable_name}` allows a variable's existence to be tested in an `\if` statement.

- Allow environment variable `PSQL_PAGER` to control psql's pager (Pavel Stehule)

  This allows psql's default pager to be specified as a separate environment variable from the pager for other applications. `PAGER` is still honored if `PSQL_PAGER` is not set.

- Make psql's `\d+` command always show the table's partitioning information (Amit Langote, Ashutosh Bapat)

  Previously, partition information would not be displayed for a partitioned table if it had no partitions. Also indicate which partitions are themselves partitioned.

- Ensure that psql reports the proper user name when prompting for a password (Tom Lane)

  Previously, combinations of `-U` and a user name embedded in a URI caused incorrect reporting. Also suppress the user name before the password prompt when `--password` is specified.

- Allow `quit` and `exit` to exit psql when given with no prior input (Bruce Momjian)

  Also print hints about how to exit when `quit` and `exit` are used alone on a line while the input buffer is not empty. Add a similar hint for `help`.

- Make psql hint at using control-D when `\q` is entered alone on a line but ignored (Bruce Momjian)

  For example, `\q` does not exit when supplied in character strings.

- Improve tab completion for `ALTER INDEX RESET`/`SET` (Masahiko Sawada)

- Add infrastructure to allow psql to adapt its tab completion queries based on the server version (Tom Lane)

  Previously, tab completion queries could fail against older servers.

##### E.16.3.8.2. pgbench

- Add pgbench expression support for NULLs, booleans, and some functions and operators (Fabien Coelho)

- Add `\if` conditional support to pgbench (Fabien Coelho)

- Allow the use of non-ASCII characters in pgbench variable names (Fabien Coelho)

- Add pgbench option `--init-steps` to control the initialization steps performed (Masahiko Sawada)

- Add an approximately Zipfian-distributed random generator to pgbench (Alik Khilazhev)

- Allow the random seed to be set in pgbench (Fabien Coelho)

- Allow pgbench to do exponentiation with `pow()` and `power()` (Raúl Marín Rodríguez)

- Add hashing functions to pgbench (Ildar Musin)

- Make pgbench statistics more accurate when using `--latency-limit` and `--rate` (Fabien Coelho)

#### E.16.3.9. Server Applications

- Add an option to pg_basebackup that creates a named replication slot (Michael Banck)

  The option `--create-slot` creates the named replication slot (`--slot`) when the WAL streaming method (`--wal-method=stream`) is used.

- Allow initdb to set group read access to the data directory (David Steele)

  This is accomplished with the new initdb option `--allow-group-access`. Administrators can also set group permissions on the empty data directory before running initdb. Server variable `data_directory_mode` allows reading of data directory group permissions.

- Add pg_verify_checksums tool to verify database checksums while offline (Magnus Hagander)

- Allow pg_resetwal to change the WAL segment size via `--wal-segsize` (Nathan Bossart)

- Add long options to pg_resetwal and pg_controldata (Nathan Bossart, Peter Eisentraut)

- Add pg_receivewal option `--no-sync` to prevent synchronous WAL writes, for testing (Michael Paquier)

- Add pg_receivewal option `--endpos` to specify when WAL receiving should stop (Michael Paquier)

- Allow pg_ctl to send the `SIGKILL` signal to processes (Andres Freund)

  This was previously unsupported due to concerns over possible misuse.

- Reduce the number of files copied by pg_rewind (Michael Paquier)

- Prevent pg_rewind from running as `root` (Michael Paquier)

##### E.16.3.9.1. pg_dump, pg_dumpall, pg_restore

- Add pg_dumpall option `--encoding` to control output encoding (Michael Paquier)

  pg_dump already had this option.

- Add pg_dump option `--load-via-partition-root` to force loading of data into the partition's root table, rather than the original partition (Rushabh Lathia)

  This is useful if the system to be loaded to has different collation definitions or endianness, possibly requiring rows to be stored in different partitions than previously.

- Add an option to suppress dumping and restoring database object comments (Robins Tharakan)

  The new pg_dump, pg_dumpall, and pg_restore option is `--no-comments`.

#### E.16.3.10. Source Code

- Add PGXS support for installing include files (Andrew Gierth)

  This supports creating extension modules that depend on other modules. Formerly there was no easy way for the dependent module to find the referenced one's include files. Several existing `contrib` modules that define data types have been adjusted to install relevant files. Also, PL/Perl and PL/Python now install their include files, to support creation of transform modules for those languages.

- Install `errcodes.txt` to allow extensions to access the list of error codes known to PostgreSQL (Thomas Munro)

- Convert documentation to DocBook XML (Peter Eisentraut, Alexander Lakhin, Jürgen Purtz)

  The file names still use an `sgml` extension for compatibility with back branches.

- Use `stdbool.h` to define type `bool` on platforms where it's suitable, which is most (Peter Eisentraut)

  This eliminates a coding hazard for extension modules that need to include `stdbool.h`.

- Overhaul the way that initial system catalog contents are defined (John Naylor)

  The initial data is now represented in Perl data structures, making it much easier to manipulate mechanically.

- Prevent extensions from creating custom server parameters that take a quoted list of values (Tom Lane)

  This cannot be supported at present because knowledge of the parameter's property would be required even before the extension is loaded.

- Add ability to use channel binding when using SCRAM authentication (Michael Paquier)

  Channel binding is intended to prevent man-in-the-middle attacks, but SCRAM cannot prevent them unless it can be forced to be active. Unfortunately, there is no way to do that in libpq. Support for it is expected in future versions of libpq and in interfaces not built using libpq, e.g. JDBC.

- Allow background workers to attach to databases that normally disallow connections (Magnus Hagander)

- Add support for hardware CRC calculations on ARMv8 (Yuqi Gu, Heikki Linnakangas, Thomas Munro)

- Speed up lookups of built-in functions by OID (Andres Freund)

  The previous binary search has been replaced by a lookup array.

- Speed up construction of query results (Andres Freund)

- Improve speed of access to system caches (Andres Freund)

- Add a generational memory allocator which is optimized for serial allocation/deallocation (Tomas Vondra)

  This reduces memory usage for logical decoding.

- Make the computation of `pg_class`.`reltuples` by `VACUUM` consistent with its computation by `ANALYZE` (Tomas Vondra)

- Update to use perltidy version `20170521` (Tom Lane, Peter Eisentraut)

#### E.16.3.11. Additional Modules

- Allow extension `pg_prewarm` to restore the previous shared buffer contents on startup (Mithun Cy, Robert Haas)

  This is accomplished by having `pg_prewarm` store the shared buffers' relation and block number data to disk occasionally during server operation, and at shutdown.

- Add `pg_trgm` function `strict_word_similarity()` to compute the similarity of whole words (Alexander Korotkov)

  The function `word_similarity()` already existed for this purpose, but it was designed to find similar parts of words, while `strict_word_similarity()` computes the similarity to whole words.

- Allow `btree_gin` to index `bool`, `bpchar`, `name` and `uuid` data types (Matheus Oliveira)

- Allow `cube` and `seg` extensions to perform index-only scans using GiST indexes (Andrey Borodin)

- Allow retrieval of negative cube coordinates using the `~>` operator (Alexander Korotkov)

  This is useful for KNN-GiST searches when looking for coordinates in descending order.

- Add Vietnamese letter handling to the `unaccent` extension (Dang Minh Huong, Michael Paquier)

- Enhance `amcheck` to check that each heap tuple has an index entry (Peter Geoghegan)

- Have `adminpack` use the new default file system access roles (Stephen Frost)

  Previously, only superusers could call `adminpack` functions; now role permissions are checked.

- Widen `pg_stat_statement`'s query ID to 64 bits (Robert Haas)

  This greatly reduces the chance of query ID hash collisions. The query ID can now potentially display as a negative value.

- Remove the `contrib/start-scripts/osx` scripts since they are no longer recommended (use `contrib/start-scripts/macos` instead) (Tom Lane)

- Remove the `chkpass` extension (Peter Eisentraut)

  This extension is no longer considered to be a usable security tool or example of how to write an extension.

### E.16.4. Acknowledgments

The following individuals (in alphabetical order) have contributed to this release as patch authors, committers, reviewers, testers, or reporters of issues.

Abhijit Menon-Sen
Adam Bielanski
Adam Brightwell
Adam Brusselback
Aditya Toshniwal
Adrián Escoms
Adrien Nayrat
Akos Vandra
Aleksander Alekseev
Aleksandr Parfenov
Alexander Korotkov
Alexander Kukushkin
Alexander Kuzmenkov
Alexander Lakhin
Alexandre Garcia
Alexey Bashtanov
Alexey Chernyshov
Alexey Kryuchkov
Alik Khilazhev
Álvaro Herrera
Amit Kapila
Amit Khandekar
Amit Langote
Amul Sul
Anastasia Lubennikova
Andreas Joseph Krogh
Andreas Karlsson
Andreas Seltenreich
André Hänsel
Andrei Gorita
Andres Freund
Andrew Dunstan
Andrew Fletcher
Andrew Gierth
Andrew Grossman
Andrew Krasichkov
Andrey Borodin
Andrey Lizenko
Andy Abelisto
Anthony Bykov
Antoine Scemama
Anton Dignös
Antonin Houska
Arseniy Sharoglazov
Arseny Sher
Arthur Zakirov
Ashutosh Bapat
Ashutosh Sharma
Ashwin Agrawal
Asim Praveen
Atsushi Torikoshi
Badrul Chowdhury
Balazs Szilfai
Basil Bourque
Beena Emerson
Ben Chobot
Benjamin Coutu
Bernd Helmle
Blaz Merela
Brad DeJong
Brent Dearth
Brian Cloutier
Bruce Momjian
Catalin Iacob
Chad Trabant
Chapman Flack
Christian Duta
Christian Ullrich
Christoph Berg
Christoph Dreis
Christophe Courtois
Christopher Jones
Claudio Freire
Clayton Salem
Craig Ringer
Dagfinn Ilmari Mannsåker
Dan Vianello
Dan Watson
Dang Minh Huong
Daniel Gustafsson
Daniel Vérité
Daniel Westermann
Daniel Wood
Darafei Praliaskouski
Dave Cramer
Dave Page
David Binderman
David Carlier
David Fetter
David G. Johnston
David Gould
David Hinkle
David Pereiro Lagares
David Rader
David Rowley
David Steele
Davy Machado
Dean Rasheed
Dian Fay
Dilip Kumar
Dmitriy Sarafannikov
Dmitry Dolgov
Dmitry Ivanov
Dmitry Shalashov
Don Seiler
Doug Doole
Doug Rady
Edmund Horner
Eiji Seki
Elvis Pranskevichus
Emre Hasegeli
Erik Rijkers
Erwin Brandstetter
Etsuro Fujita
Euler Taveira
Everaldo Canuto
Fabien Coelho
Fabrízio de Royes Mello
Feike Steenbergen
Frits Jalvingh
Fujii Masao
Gao Zengqi
Gianni Ciolli
Greg Stark
Gunnlaugur Thor Briem
Guo Xiang Tan
Hadi Moshayedi
Hailong Li
Haribabu Kommi
Heath Lord
Heikki Linnakangas
Hugo Mercier
Igor Korot
Igor Neyman
Ildar Musin
Ildus Kurbangaliev
Ioseph Kim
Jacob Champion
Jaime Casanova
Jakob Egger
Jean-Pierre Pelletier
Jeevan Chalke
Jeevan Ladhe
Jeff Davis
Jeff Janes
Jeremy Evans
Jeremy Finzel
Jeremy Schneider
Jesper Pedersen
Jim Nasby
Jimmy Yih
Jing Wang
Jobin Augustine
Joe Conway
John Gorman
John Naylor
Jon Nelson
Jon Wolski
Jonathan Allen
Jonathan S. Katz
Julien Rouhaud
Jürgen Purtz
Justin Pryzby
KaiGai Kohei
Kaiting Chen
Karl Lehenbauer
Keith Fiske
Kevin Bloch
Kha Nguyen
Kim Rose Carlsen
Konstantin Knizhnik
Kuntal Ghosh
Kyle Samson
Kyotaro Horiguchi
Lætitia Avrot
Lars Kanis
Laurenz Albe
Leonardo Cecchi
Liudmila Mantrova
Lixian Zou
Lloyd Albin
Luca Ferrari
Lucas Fairchild
Lukas Eder
Lukas Fittl
Magnus Hagander
Mai Peng
Maksim Milyutin
Maksym Boguk
Mansur Galiev
Marc Dilger
Marco Nenciarini
Marina Polyakova
Mario de Frutos Dieguez
Mark Cave-Ayland
Mark Dilger
Mark Wood
Marko Tiikkaja
Markus Winand
Martín Marqués
Masahiko Sawada
Matheus Oliveira
Matthew Stickney
Metin Doslu
Michael Banck
Michael Meskes
Michael Paquier
Michail Nikolaev
Mike Blackwell
Minh-Quan Tran
Mithun Cy
Morgan Owens
Nathan Bossart
Nathan Wagner
Neil Conway
Nick Barnes
Nicolas Thauvin
Nikhil Sontakke
Nikita Glukhov
Nikolay Shaplov
Noah Misch
Noriyoshi Shinoda
Oleg Bartunov
Oleg Samoilov
Oliver Ford
Pan Bian
Pascal Legrand
Patrick Hemmer
Patrick Krecker
Paul Bonaud
Paul Guo
Paul Ramsey
Pavan Deolasee
Pavan Maddamsetti
Pavel Golub
Pavel Stehule
Peter Eisentraut
Peter Geoghegan
Petr Jelínek
Petru-Florin Mihancea
Phil Florent
Philippe Beaudoin
Pierre Ducroquet
Piotr Stefaniak
Prabhat Sahu
Pu Qun
QL Zhuo
Rafia Sabih
Rahila Syed
Rainer Orth
Rajkumar Raghuwanshi
Raúl Marín Rodríguez
Regina Obe
Richard Yen
Robert Haas
Robins Tharakan
Rod Taylor
Rushabh Lathia
Ryan Murphy
Sahap Asci
Samuel Horwitz
Scott Ure
Sean Johnston
Shao Bret
Shay Rojansky
Shubham Barai
Simon Riggs
Simone Gotti
Sivasubramanian Ramasubramanian
Stas Kelvich
Stefan Kaltenbrunner
Stephen Froehlich
Stephen Frost
Steve Singer
Steven Winfield
Sven Kunze
Taiki Kondo
Takayuki Tsunakawa
Takeshi Ideriha
Tatsuo Ishii
Tatsuro Yamada
Teodor Sigaev
Thom Brown
Thomas Kellerer
Thomas Munro
Thomas Reiss
Tobias Bussmann
Todd A. Cook
Tom Kazimiers
Tom Lane
Tomas Vondra
Tomonari Katsumata
Torsten Grust
Tushar Ahuja
Vaishnavi Prabakaran
Vasundhar Boddapati
Victor Drobny
Victor Wagner
Victor Yegorov
Vik Fearing
Vinayak Pokale
Vincent Lachenal
Vitaliy Garnashevich
Vitaly Burovoy
Vladimir Baranoff
Xin Zhang
Yi Wen Wong
Yorick Peterse
Yugo Nagata
Yuqi Gu
Yura Sokolov
Yves Goergen
Zhou Digoal