E.20. Release 10
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## E.20. Release 10

Release date: 2017-10-05

### E.20.1. Overview

Major enhancements in PostgreSQL 10 include:

- Logical replication using publish/subscribe

- Declarative table partitioning

- Improved query parallelism

- Significant general performance improvements

- Stronger password authentication based on SCRAM-SHA-256

- Improved monitoring and control

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

### E.20.2. Migration to Version 10

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 18.6 for general information on migrating to new major releases.

Version 10 contains a number of changes that may affect compatibility with previous releases. Observe the following incompatibilities:

- Hash indexes must be rebuilt after pg_upgrade-ing from any previous major PostgreSQL version (Mithun Cy, Robert Haas, Amit Kapila)

  Major hash index improvements necessitated this requirement. pg_upgrade will create a script to assist with this.

- Rename write-ahead log directory `pg_xlog` to `pg_wal`, and rename transaction status directory `pg_clog` to `pg_xact` (Michael Paquier)

  Users have occasionally thought that these directories contained only inessential log files, and proceeded to remove write-ahead log files or transaction status files manually, causing irrecoverable data loss. These name changes are intended to discourage such errors in future.

- Rename SQL functions, tools, and options that reference “xlog” to “wal” (Robert Haas)

  For example, `pg_switch_xlog()` becomes `pg_switch_wal()`, pg_receivexlog becomes pg_receivewal, and `--xlogdir` becomes `--waldir`. This is for consistency with the change of the `pg_xlog` directory name; in general, the “xlog” terminology is no longer used in any user-facing places.

- Rename WAL-related functions and views to use `lsn` instead of `location` (David Rowley)

  There was previously an inconsistent mixture of the two terminologies.

- Change the implementation of set-returning functions appearing in a query's `SELECT` list (Andres Freund)

  Set-returning functions are now evaluated before evaluation of scalar expressions in the `SELECT` list, much as though they had been placed in a `LATERAL FROM`-clause item. This allows saner semantics for cases where multiple set-returning functions are present. If they return different numbers of rows, the shorter results are extended to match the longest result by adding nulls. Previously the results were cycled until they all terminated at the same time, producing a number of rows equal to the least common multiple of the functions' periods. In addition, set-returning functions are now disallowed within `CASE` and `COALESCE` constructs. For more information see Section 37.4.8.

- Use standard row constructor syntax in `UPDATE ... SET (`column_list`) = `row_constructor`` (Tom Lane)

  The `row_constructor` can now begin with the keyword `ROW`; previously that had to be omitted. If just one column name appears in the `column_list`, then the `row_constructor` now must use the `ROW` keyword, since otherwise it is not a valid row constructor but just a parenthesized expression. Also, an occurrence of ``table_name`.*` within the `row_constructor` is now expanded into multiple columns, as occurs in other uses of `row_constructor`s.

- When `ALTER TABLE ... ADD PRIMARY KEY` marks columns `NOT NULL`, that change now propagates to inheritance child tables as well (Michael Paquier)

- Prevent statement-level triggers from firing more than once per statement (Tom Lane)

  Cases involving writable CTEs updating the same table updated by the containing statement, or by another writable CTE, fired `BEFORE STATEMENT` or `AFTER STATEMENT` triggers more than once. Also, if there were statement-level triggers on a table affected by a foreign key enforcement action (such as `ON DELETE CASCADE`), they could fire more than once per outer SQL statement. This is contrary to the SQL standard, so change it.

- Move sequences' metadata fields into a new `pg_sequence` system catalog (Peter Eisentraut)

  A sequence relation now stores only the fields that can be modified by `nextval()`, that is `last_value`, `log_cnt`, and `is_called`. Other sequence properties, such as the starting value and increment, are kept in a corresponding row of the `pg_sequence` catalog. `ALTER SEQUENCE` updates are now fully transactional, implying that the sequence is locked until commit. The `nextval()` and `setval()` functions remain nontransactional.

  The main incompatibility introduced by this change is that selecting from a sequence relation now returns only the three fields named above. To obtain the sequence's other properties, applications must look into `pg_sequence`. The new system view `pg_sequences` can also be used for this purpose; it provides column names that are more compatible with existing code.

  Also, sequences created for `SERIAL` columns now generate positive 32-bit wide values, whereas previous versions generated 64-bit wide values. This has no visible effect if the values are only stored in a column.

  The output of psql's `\d` command for a sequence has been redesigned, too.

- Make pg_basebackup stream the WAL needed to restore the backup by default (Magnus Hagander)

  This changes pg_basebackup's `-X`/`--wal-method` default to `stream`. An option value `none` has been added to reproduce the old behavior. The pg_basebackup option `-x` has been removed (instead, use `-X fetch`).

- Change how logical replication uses `pg_hba.conf` (Peter Eisentraut)

  In previous releases, a logical replication connection required the `replication` keyword in the database column. As of this release, logical replication matches a normal entry with a database name or keywords such as `all`. Physical replication continues to use the `replication` keyword. Since built-in logical replication is new in this release, this change only affects users of third-party logical replication plugins.

- Make all pg_ctl actions wait for completion by default (Peter Eisentraut)

  Previously some pg_ctl actions didn't wait for completion, and required the use of `-w` to do so.

- Change the default value of the log_directory server parameter from `pg_log` to `log` (Andreas Karlsson)

- Add configuration option ssl_dh_params_file to specify file name for custom OpenSSL DH parameters (Heikki Linnakangas)

  This replaces the hardcoded, undocumented file name `dh1024.pem`. Note that `dh1024.pem` is no longer examined by default; you must set this option if you want to use custom DH parameters.

- Increase the size of the default DH parameters used for OpenSSL ephemeral DH ciphers to 2048 bits (Heikki Linnakangas)

  The size of the compiled-in DH parameters has been increased from 1024 to 2048 bits, making DH key exchange more resistant to brute-force attacks. However, some old SSL implementations, notably some revisions of Java Runtime Environment version 6, will not accept DH parameters longer than 1024 bits, and hence will not be able to connect over SSL. If it's necessary to support such old clients, you can use custom 1024-bit DH parameters instead of the compiled-in defaults. See ssl_dh_params_file.

- Remove the ability to store unencrypted passwords on the server (Heikki Linnakangas)

  The password_encryption server parameter no longer supports `off` or `plain`. The `UNENCRYPTED` option is no longer supported in `CREATE/ALTER USER ... PASSWORD`. Similarly, the `--unencrypted` option has been removed from createuser. Unencrypted passwords migrated from older versions will be stored encrypted in this release. The default setting for `password_encryption` is still `md5`.

- Add min_parallel_table_scan_size and min_parallel_index_scan_size server parameters to control parallel queries (Amit Kapila, Robert Haas)

  These replace `min_parallel_relation_size`, which was found to be too generic.

- Don't downcase unquoted text within shared_preload_libraries and related server parameters (QL Zhuo)

  These settings are really lists of file names, but they were previously treated as lists of SQL identifiers, which have different parsing rules.

- Remove `sql_inheritance` server parameter (Robert Haas)

  Changing this setting from the default value caused queries referencing parent tables to not include child tables. The SQL standard requires them to be included, however, and this has been the default since PostgreSQL 7.1.

- Allow multi-dimensional arrays to be passed into PL/Python functions, and returned as nested Python lists (Alexey Grishchenko, Dave Cramer, Heikki Linnakangas)

  This feature requires a backwards-incompatible change to the handling of arrays of composite types in PL/Python. Previously, you could return an array of composite values by writing, e.g., `[[col1, col2], [col1, col2]]`; but now that is interpreted as a two-dimensional array. Composite types in arrays must now be written as Python tuples, not lists, to resolve the ambiguity; that is, write `[(col1, col2), (col1, col2)]` instead.

- Remove PL/Tcl's “module” auto-loading facility (Tom Lane)

  This functionality has been replaced by new server parameters pltcl.start_proc and pltclu.start_proc, which are easier to use and more similar to features available in other PLs.

- Remove pg_dump/pg_dumpall support for dumping from pre-8.0 servers (Tom Lane)

  Users needing to dump from pre-8.0 servers will need to use dump programs from PostgreSQL 9.6 or earlier. The resulting output should still load successfully into newer servers.

- Remove support for floating-point timestamps and intervals (Tom Lane)

  This removes configure's `--disable-integer-datetimes` option. Floating-point timestamps have few advantages and have not been the default since PostgreSQL 8.3.

- Remove server support for client/server protocol version 1.0 (Tom Lane)

  This protocol hasn't had client support since PostgreSQL 6.3.

- Remove `contrib/tsearch2` module (Robert Haas)

  This module provided compatibility with the version of full text search that shipped in pre-8.3 PostgreSQL releases.

- Remove createlang and droplang command-line applications (Peter Eisentraut)

  These had been deprecated since PostgreSQL 9.1. Instead, use `CREATE EXTENSION` and `DROP EXTENSION` directly.

- Remove support for version-0 function calling conventions (Andres Freund)

  Extensions providing C-coded functions must now conform to version 1 calling conventions. Version 0 has been deprecated since 2001.

### E.20.3. Changes

Below you will find a detailed account of the changes between PostgreSQL 10 and the previous major release.

#### E.20.3.1. Server

##### E.20.3.1.1. Parallel Queries

- Support parallel B-tree index scans (Rahila Syed, Amit Kapila, Robert Haas, Rafia Sabih)

  This change allows B-tree index pages to be searched by separate parallel workers.

- Support parallel bitmap heap scans (Dilip Kumar)

  This allows a single index scan to dispatch parallel workers to process different areas of the heap.

- Allow merge joins to be performed in parallel (Dilip Kumar)

- Allow non-correlated subqueries to be run in parallel (Amit Kapila)

- Improve ability of parallel workers to return pre-sorted data (Rushabh Lathia)

- Increase parallel query usage in procedural language functions (Robert Haas, Rafia Sabih)

- Add max_parallel_workers server parameter to limit the number of worker processes that can be used for query parallelism (Julien Rouhaud)

  This parameter can be set lower than max_worker_processes to reserve worker processes for purposes other than parallel queries.

- Enable parallelism by default by changing the default setting of max_parallel_workers_per_gather to `2`.

##### E.20.3.1.2. Indexes

- Add write-ahead logging support to hash indexes (Amit Kapila)

  This makes hash indexes crash-safe and replicatable. The former warning message about their use is removed.

- Improve hash index performance (Amit Kapila, Mithun Cy, Ashutosh Sharma)

- Add SP-GiST index support for `INET` and `CIDR` data types (Emre Hasegeli)

- Add option to allow BRIN index summarization to happen more aggressively (Álvaro Herrera)

  A new `CREATE INDEX` option enables auto-summarization of the previous BRIN page range when a new page range is created.

- Add functions to remove and re-add BRIN summarization for BRIN index ranges (Álvaro Herrera)

  The new SQL function `brin_summarize_range()` updates BRIN index summarization for a specified range and `brin_desummarize_range()` removes it. This is helpful to update summarization of a range that is now smaller due to `UPDATE`s and `DELETE`s.

- Improve accuracy in determining if a BRIN index scan is beneficial (David Rowley, Emre Hasegeli)

- Allow faster GiST inserts and updates by reusing index space more efficiently (Andrey Borodin)

- Reduce page locking during vacuuming of GIN indexes (Andrey Borodin)

##### E.20.3.1.3. Locking

- Reduce locking required to change table parameters (Simon Riggs, Fabrízio Mello)

  For example, changing a table's effective_io_concurrency setting can now be done with a more lightweight lock.

- Allow tuning of predicate lock promotion thresholds (Dagfinn Ilmari Mannsåker)

  Lock promotion can now be controlled through two new server parameters, max_pred_locks_per_relation and max_pred_locks_per_page.

##### E.20.3.1.4. Optimizer

- Add multi-column optimizer statistics to compute the correlation ratio and number of distinct values (Tomas Vondra, David Rowley, Álvaro Herrera)

  New commands are `CREATE STATISTICS`, `ALTER STATISTICS`, and `DROP STATISTICS`. This feature is helpful in estimating query memory usage and when combining the statistics from individual columns.

- Improve performance of queries affected by row-level security restrictions (Tom Lane)

  The optimizer now has more knowledge about where it can place RLS filter conditions, allowing better plans to be generated while still enforcing the RLS conditions safely.

##### E.20.3.1.5. General Performance

- Speed up aggregate functions that calculate a running sum using `numeric`-type arithmetic, including some variants of `SUM()`, `AVG()`, and `STDDEV()` (Heikki Linnakangas)

- Improve performance of character encoding conversions by using radix trees (Kyotaro Horiguchi, Heikki Linnakangas)

- Reduce expression evaluation overhead during query execution, as well as plan node calling overhead (Andres Freund)

  This is particularly helpful for queries that process many rows.

- Allow hashed aggregation to be used with grouping sets (Andrew Gierth)

- Use uniqueness guarantees to optimize certain join types (David Rowley)

- Improve sort performance of the `macaddr` data type (Brandur Leach)

- Reduce statistics tracking overhead in sessions that reference many thousands of relations (Aleksander Alekseev)

##### E.20.3.1.6. Monitoring

- Allow explicit control over `EXPLAIN`'s display of planning and execution time (Ashutosh Bapat)

  By default planning and execution time are displayed by `EXPLAIN ANALYZE` and are not displayed in other cases. The new `EXPLAIN` option `SUMMARY` allows explicit control of this.

- Add default monitoring roles (Dave Page)

  New roles `pg_monitor`, `pg_read_all_settings`, `pg_read_all_stats`, and `pg_stat_scan_tables` allow simplified permission configuration.

- Properly update the statistics collector during `REFRESH MATERIALIZED VIEW` (Jim Mlodgenski)

###### E.20.3.1.6.1. Logging

- Change the default value of log_line_prefix to include current timestamp (with milliseconds) and the process ID in each line of postmaster log output (Christoph Berg)

  The previous default was an empty prefix.

- Add functions to return the log and WAL directory contents (Dave Page)

  The new functions are `pg_ls_logdir()` and `pg_ls_waldir()` and can be executed by non-superusers with the proper permissions.

- Add function `pg_current_logfile()` to read logging collector's current stderr and csvlog output file names (Gilles Darold)

- Report the address and port number of each listening socket in the server log during postmaster startup (Tom Lane)

  Also, when logging failure to bind a listening socket, include the specific address we attempted to bind to.

- Reduce log chatter about the starting and stopping of launcher subprocesses (Tom Lane)

  These are now `DEBUG1`-level messages.

- Reduce message verbosity of lower-numbered debug levels controlled by log_min_messages (Robert Haas)

  This also changes the verbosity of client_min_messages debug levels.

###### E.20.3.1.6.2. `pg_stat_activity`

- Add `pg_stat_activity` reporting of low-level wait states (Michael Paquier, Robert Haas, Rushabh Lathia)

  This change enables reporting of numerous low-level wait conditions, including latch waits, file reads/writes/fsyncs, client reads/writes, and synchronous replication.

- Show auxiliary processes, background workers, and walsender processes in `pg_stat_activity` (Kuntal Ghosh, Michael Paquier)

  This simplifies monitoring. A new column `backend_type` identifies the process type.

- Allow `pg_stat_activity` to show the SQL query being executed by parallel workers (Rafia Sabih)

- Rename `pg_stat_activity`.`wait_event_type` values `LWLockTranche` and `LWLockNamed` to `LWLock` (Robert Haas)

  This makes the output more consistent.

##### E.20.3.1.7. Authentication

- Add SCRAM-SHA-256 support for password negotiation and storage (Michael Paquier, Heikki Linnakangas)

  This provides better security than the existing `md5` negotiation and storage method.

- Change the password_encryption server parameter from `boolean` to `enum` (Michael Paquier)

  This was necessary to support additional password hashing options.

- Add view `pg_hba_file_rules` to display the contents of `pg_hba.conf` (Haribabu Kommi)

  This shows the file contents, not the currently active settings.

- Support multiple RADIUS servers (Magnus Hagander)

  All the RADIUS related parameters are now plural and support a comma-separated list of servers.

##### E.20.3.1.8. Server Configuration

- Allow SSL configuration to be updated during configuration reload (Andreas Karlsson, Tom Lane)

  This allows SSL to be reconfigured without a server restart, by using `pg_ctl reload`, `SELECT pg_reload_conf()`, or sending a `SIGHUP` signal. However, reloading the SSL configuration does not work if the server's SSL key requires a passphrase, as there is no way to re-prompt for the passphrase. The original configuration will apply for the life of the postmaster in that case.

- Make the maximum value of bgwriter_lru_maxpages effectively unlimited (Jim Nasby)

##### E.20.3.1.9. Reliability

- After creating or unlinking files, perform an fsync on their parent directory (Michael Paquier)

  This reduces the risk of data loss after a power failure.

###### E.20.3.1.9.1. Write-Ahead Log (WAL)

- Prevent unnecessary checkpoints and WAL archiving on otherwise-idle systems (Michael Paquier)

- Add wal_consistency_checking server parameter to add details to WAL that can be sanity-checked on the standby (Kuntal Ghosh, Robert Haas)

  Any sanity-check failure generates a fatal error on the standby.

- Increase the maximum configurable WAL segment size to one gigabyte (Beena Emerson)

  A larger WAL segment size allows for fewer archive_command invocations and fewer WAL files to manage.

#### E.20.3.2. Replication and Recovery

- Add the ability to logically replicate tables to standby servers (Petr Jelinek)

  Logical replication allows more flexibility than physical replication does, including replication between different major versions of PostgreSQL and selective replication.

- Allow waiting for commit acknowledgment from standby servers irrespective of the order they appear in synchronous_standby_names (Masahiko Sawada)

  Previously the server always waited for the active standbys that appeared first in `synchronous_standby_names`. The new `synchronous_standby_names` keyword `ANY` allows waiting for any number of standbys irrespective of their ordering. This is known as quorum commit.

- Reduce configuration changes necessary to perform streaming backup and replication (Magnus Hagander, Dang Minh Huong)

  Specifically, the defaults were changed for wal_level, max_wal_senders, max_replication_slots, and hot_standby to make them suitable for these usages out-of-the-box.

- Enable replication from localhost connections by default in `pg_hba.conf` (Michael Paquier)

  Previously `pg_hba.conf`'s replication connection lines were commented out by default. This is particularly useful for pg_basebackup.

- Add columns to `pg_stat_replication` to report replication delay times (Thomas Munro)

  The new columns are `write_lag`, `flush_lag`, and `replay_lag`.

- Allow specification of the recovery stopping point by Log Sequence Number (LSN) in `recovery.conf` (Michael Paquier)

  Previously the stopping point could only be selected by timestamp or XID.

- Allow users to disable `pg_stop_backup()`'s waiting for all WAL to be archived (David Steele)

  An optional second argument to `pg_stop_backup()` controls that behavior.

- Allow creation of temporary replication slots (Petr Jelinek)

  Temporary slots are automatically removed on session exit or error.

- Improve performance of hot standby replay with better tracking of Access Exclusive locks (Simon Riggs, David Rowley)

- Speed up two-phase commit recovery performance (Stas Kelvich, Nikhil Sontakke, Michael Paquier)

#### E.20.3.3. Queries

- Add `XMLTABLE` function that converts `XML`-formatted data into a row set (Pavel Stehule, Álvaro Herrera)

- Fix regular expressions' character class handling for large character codes, particularly Unicode characters above `U+7FF` (Tom Lane)

  Previously, such characters were never recognized as belonging to locale-dependent character classes such as `[[:alpha:]]`.

#### E.20.3.4. Utility Commands

- Add table partitioning syntax that automatically creates partition constraints and handles routing of tuple insertions and updates (Amit Langote)

  The syntax supports range and list partitioning.

- Add `AFTER` trigger transition tables to record changed rows (Kevin Grittner, Thomas Munro)

  Transition tables are accessible from triggers written in server-side languages.

- Allow restrictive row-level security policies (Stephen Frost)

  Previously all security policies were permissive, meaning that any matching policy allowed access. A restrictive policy must match for access to be granted. These policy types can be combined.

- When creating a foreign-key constraint, check for `REFERENCES` permission on only the referenced table (Tom Lane)

  Previously `REFERENCES` permission on the referencing table was also required. This appears to have stemmed from a misreading of the SQL standard. Since creating a foreign key (or any other type of) constraint requires ownership privilege on the constrained table, additionally requiring `REFERENCES` permission seems rather pointless.

- Allow default permissions on schemas (Matheus Oliveira)

  This is done using the `ALTER DEFAULT PRIVILEGES` command.

- Add `CREATE SEQUENCE AS` command to create a sequence matching an integer data type (Peter Eisentraut)

  This simplifies the creation of sequences matching the range of base columns.

- Allow `COPY `view` FROM `source`` on views with `INSTEAD INSERT` triggers (Haribabu Kommi)

  The triggers are fed the data rows read by `COPY`.

- Allow the specification of a function name without arguments in DDL commands, if it is unique (Peter Eisentraut)

  For example, allow `DROP FUNCTION` on a function name without arguments if there is only one function with that name. This behavior is required by the SQL standard.

- Allow multiple functions, operators, and aggregates to be dropped with a single `DROP` command (Peter Eisentraut)

- Support `IF NOT EXISTS` in `CREATE SERVER`, `CREATE USER MAPPING`, and `CREATE COLLATION` (Anastasia Lubennikova, Peter Eisentraut)

- Make `VACUUM VERBOSE` report the number of skipped frozen pages and oldest xmin (Masahiko Sawada, Simon Riggs)

  This information is also included in log_autovacuum_min_duration output.

- Improve speed of `VACUUM`'s removal of trailing empty heap pages (Claudio Freire, Álvaro Herrera)

#### E.20.3.5. Data Types

- Add full text search support for `JSON` and `JSONB` (Dmitry Dolgov)

  The functions `ts_headline()` and `to_tsvector()` can now be used on these data types.

- Add support for EUI-64 MAC addresses, as a new data type `macaddr8` (Haribabu Kommi)

  This complements the existing support for EUI-48 MAC addresses (type `macaddr`).

- Add identity columns for assigning a numeric value to columns on insert (Peter Eisentraut)

  These are similar to `SERIAL` columns, but are SQL standard compliant.

- Allow `ENUM` values to be renamed (Dagfinn Ilmari Mannsåker)

  This uses the syntax `ALTER TYPE ... RENAME VALUE`.

- Properly treat array pseudotypes (`anyarray`) as arrays in `to_json()` and `to_jsonb()` (Andrew Dunstan)

  Previously columns declared as `anyarray` (particularly those in the `pg_stats` view) were converted to `JSON` strings rather than arrays.

- Add operators for multiplication and division of `money` values with `int8` values (Peter Eisentraut)

  Previously such cases would result in converting the `int8` values to `float8` and then using the `money`-and-`float8` operators. The new behavior avoids possible precision loss. But note that division of `money` by `int8` now truncates the quotient, like other integer-division cases, while the previous behavior would have rounded.

- Check for overflow in the `money` type's input function (Peter Eisentraut)

#### E.20.3.6. Functions

- Add simplified `regexp_match()` function (Emre Hasegeli)

  This is similar to `regexp_matches()`, but it only returns results from the first match so it does not need to return a set, making it easier to use for simple cases.

- Add a version of `jsonb`'s delete operator that takes an array of keys to delete (Magnus Hagander)

- Make `json_populate_record()` and related functions process JSON arrays and objects recursively (Nikita Glukhov)

  With this change, array-type fields in the destination SQL type are properly converted from JSON arrays, and composite-type fields are properly converted from JSON objects. Previously, such cases would fail because the text representation of the JSON value would be fed to `array_in()` or `record_in()`, and its syntax would not match what those input functions expect.

- Add function `txid_current_if_assigned()` to return the current transaction ID or `NULL` if no transaction ID has been assigned (Craig Ringer)

  This is different from `txid_current()`, which always returns a transaction ID, assigning one if necessary. Unlike that function, this function can be run on standby servers.

- Add function `txid_status()` to check if a transaction was committed (Craig Ringer)

  This is useful for checking after an abrupt disconnection whether your previous transaction committed and you just didn't receive the acknowledgment.

- Allow `make_date()` to interpret negative years as BC years (Álvaro Herrera)

- Make `to_timestamp()` and `to_date()` reject out-of-range input fields (Artur Zakirov)

  For example, previously `to_date('2009-06-40','YYYY-MM-DD')` was accepted and returned `2009-07-10`. It will now generate an error.

#### E.20.3.7. Server-Side Languages

- Allow PL/Python's `cursor()` and `execute()` functions to be called as methods of their plan-object arguments (Peter Eisentraut)

  This allows a more object-oriented programming style.

- Allow PL/pgSQL's `GET DIAGNOSTICS` statement to retrieve values into array elements (Tom Lane)

  Previously, a syntactic restriction prevented the target variable from being an array element.

##### E.20.3.7.1. PL/Tcl

- Allow PL/Tcl functions to return composite types and sets (Karl Lehenbauer)

- Add a subtransaction command to PL/Tcl (Victor Wagner)

  This allows PL/Tcl queries to fail without aborting the entire function.

- Add server parameters pltcl.start_proc and pltclu.start_proc, to allow initialization functions to be called on PL/Tcl startup (Tom Lane)

#### E.20.3.8. Client Interfaces

- Allow specification of multiple host names or addresses in libpq connection strings and URIs (Robert Haas, Heikki Linnakangas)

  libpq will connect to the first responsive server in the list.

- Allow libpq connection strings and URIs to request a read/write host, that is a master server rather than a standby server (Victor Wagner, Mithun Cy)

  This is useful when multiple host names are specified. It is controlled by libpq connection parameter `target_session_attrs`.

- Allow the password file name to be specified as a libpq connection parameter (Julian Markwort)

  Previously this could only be specified via an environment variable.

- Add function `PQencryptPasswordConn()` to allow creation of more types of encrypted passwords on the client side (Michael Paquier, Heikki Linnakangas)

  Previously only `MD5`-encrypted passwords could be created using `PQencryptPassword()`. This new function can also create `SCRAM-SHA-256`-encrypted passwords.

- Change ecpg preprocessor version from 4.12 to 10 (Tom Lane)

  Henceforth the ecpg version will match the PostgreSQL distribution version number.

#### E.20.3.9. Client Applications

##### E.20.3.9.1. psql

- Add conditional branch support to psql (Corey Huinker)

  This feature adds psql meta-commands `\if`, `\elif`, `\else`, and `\endif`. This is primarily helpful for scripting.

- Add psql `\gx` meta-command to execute (`\g`) a query in expanded mode (`\x`) (Christoph Berg)

- Expand psql variable references in backtick-executed strings (Tom Lane)

  This is particularly useful in the new psql conditional branch commands.

- Prevent psql's special variables from being set to invalid values (Daniel Vérité, Tom Lane)

  Previously, setting one of psql's special variables to an invalid value silently resulted in the default behavior. `\set` on a special variable now fails if the proposed new value is invalid. As a special exception, `\set` with an empty or omitted new value, on a boolean-valued special variable, still has the effect of setting the variable to `on`; but now it actually acquires that value rather than an empty string. `\unset` on a special variable now explicitly sets the variable to its default value, which is also the value it acquires at startup. In sum, a control variable now always has a displayable value that reflects what psql is actually doing.

- Add variables showing server version and psql version (Fabien Coelho)

- Improve psql's `\d` (display relation) and `\dD` (display domain) commands to show collation, nullable, and default properties in separate columns (Peter Eisentraut)

  Previously they were shown in a single “Modifiers” column.

- Make the various `\d` commands handle no-matching-object cases more consistently (Daniel Gustafsson)

  They now all print the message about that to stderr, not stdout, and the message wording is more consistent.

- Improve psql's tab completion (Jeff Janes, Ian Barwick, Andreas Karlsson, Sehrope Sarkuni, Thomas Munro, Kevin Grittner, Dagfinn Ilmari Mannsåker)

##### E.20.3.9.2. pgbench

- Add pgbench option `--log-prefix` to control the log file prefix (Masahiko Sawada)

- Allow pgbench's meta-commands to span multiple lines (Fabien Coelho)

  A meta-command can now be continued onto the next line by writing backslash-return.

- Remove restriction on placement of `-M` option relative to other command line options (Tom Lane)

#### E.20.3.10. Server Applications

- Add pg_receivewal option `-Z`/`--compress` to specify compression (Michael Paquier)

- Add pg_recvlogical option `--endpos` to specify the ending position (Craig Ringer)

  This complements the existing `--startpos` option.

- Rename initdb options `--noclean` and `--nosync` to be spelled `--no-clean` and `--no-sync` (Vik Fearing, Peter Eisentraut)

  The old spellings are still supported.

##### E.20.3.10.1. pg_dump, pg_dumpall, pg_restore

- Allow pg_restore to exclude schemas (Michael Banck)

  This adds a new `-N`/`--exclude-schema` option.

- Add `--no-blobs` option to pg_dump (Guillaume Lelarge)

  This suppresses dumping of large objects.

- Add pg_dumpall option `--no-role-passwords` to omit role passwords (Robins Tharakan, Simon Riggs)

  This allows use of pg_dumpall by non-superusers; without this option, it fails due to inability to read passwords.

- Support using synchronized snapshots when dumping from a standby server (Petr Jelinek)

- Issue `fsync()` on the output files generated by pg_dump and pg_dumpall (Michael Paquier)

  This provides more security that the output is safely stored on disk before the program exits. This can be disabled with the new `--no-sync` option.

##### E.20.3.10.2. pg_basebackup

- Allow pg_basebackup to stream write-ahead log in tar mode (Magnus Hagander)

  The WAL will be stored in a separate tar file from the base backup.

- Make pg_basebackup use temporary replication slots (Magnus Hagander)

  Temporary replication slots will be used by default when pg_basebackup uses WAL streaming with default options.

- Be more careful about fsync'ing in all required places in pg_basebackup and pg_receivewal (Michael Paquier)

- Add pg_basebackup option `--no-sync` to disable fsync (Michael Paquier)

- Improve pg_basebackup's handling of which directories to skip (David Steele)

##### E.20.3.10.3. pg_ctl

- Add wait option for pg_ctl's promote operation (Peter Eisentraut)

- Add long options for pg_ctl wait (`--wait`) and no-wait (`--no-wait`) (Vik Fearing)

- Add long option for pg_ctl server options (`--options`) (Peter Eisentraut)

- Make `pg_ctl start --wait` detect server-ready by watching `postmaster.pid`, not by attempting connections (Tom Lane)

  The postmaster has been changed to report its ready-for-connections status in `postmaster.pid`, and pg_ctl now examines that file to detect whether startup is complete. This is more efficient and reliable than the old method, and it eliminates postmaster log entries about rejected connection attempts during startup.

- Reduce pg_ctl's reaction time when waiting for postmaster start/stop (Tom Lane)

  pg_ctl now probes ten times per second when waiting for a postmaster state change, rather than once per second.

- Ensure that pg_ctl exits with nonzero status if an operation being waited for does not complete within the timeout (Peter Eisentraut)

  The `start` and `promote` operations now return exit status 1, not 0, in such cases. The `stop` operation has always done that.

#### E.20.3.11. Source Code

- Change to two-part release version numbering (Peter Eisentraut, Tom Lane)

  Release numbers will now have two parts (e.g., `10.1`) rather than three (e.g., `9.6.3`). Major versions will now increase just the first number, and minor releases will increase just the second number. Release branches will be referred to by single numbers (e.g., `10` rather than `9.6`). This change is intended to reduce user confusion about what is a major or minor release of PostgreSQL.

- Improve behavior of pgindent (Piotr Stefaniak, Tom Lane)

  We have switched to a new version of pg_bsd_indent based on recent improvements made by the FreeBSD project. This fixes numerous small bugs that led to odd C code formatting decisions. Most notably, lines within parentheses (such as in a multi-line function call) are now uniformly indented to match the opening paren, even if that would result in code extending past the right margin.

- Allow the ICU library to optionally be used for collation support (Peter Eisentraut)

  The ICU library has versioning that allows detection of collation changes between versions. It is enabled via configure option `--with-icu`. The default still uses the operating system's native collation library.

- Automatically mark all `PG_FUNCTION_INFO_V1` functions as `DLLEXPORT`-ed on Windows (Laurenz Albe)

  If third-party code is using `extern` function declarations, they should also add `DLLEXPORT` markers to those declarations.

- Remove SPI functions `SPI_push()`, `SPI_pop()`, `SPI_push_conditional()`, `SPI_pop_conditional()`, and `SPI_restore_connection()` as unnecessary (Tom Lane)

  Their functionality now happens automatically. There are now no-op macros by these names so that external modules don't need to be updated immediately, but eventually such calls should be removed.

  A side effect of this change is that `SPI_palloc()` and allied functions now require an active SPI connection; they do not degenerate to simple `palloc()` if there is none. That previous behavior was not very useful and posed risks of unexpected memory leaks.

- Allow shared memory to be dynamically allocated (Thomas Munro, Robert Haas)

- Add slab-like memory allocator for efficient fixed-size allocations (Tomas Vondra)

- Use POSIX semaphores rather than SysV semaphores on Linux and FreeBSD (Tom Lane)

  This avoids platform-specific limits on SysV semaphore usage.

- Improve support for 64-bit atomics (Andres Freund)

- Enable 64-bit atomic operations on ARM64 (Roman Shaposhnik)

- Switch to using `clock_gettime()`, if available, for duration measurements (Tom Lane)

  `gettimeofday()` is still used if `clock_gettime()` is not available.

- Add more robust random number generators to be used for cryptographically secure uses (Magnus Hagander, Michael Paquier, Heikki Linnakangas)

  If no strong random number generator can be found, configure will fail unless the `--disable-strong-random` option is used. However, with this option, pgcrypto functions requiring a strong random number generator will be disabled.

- Allow `WaitLatchOrSocket()` to wait for socket connection on Windows (Andres Freund)

- `tupconvert.c` functions no longer convert tuples just to embed a different composite-type OID in them (Ashutosh Bapat, Tom Lane)

  The majority of callers don't care about the composite-type OID; but if the result tuple is to be used as a composite Datum, steps should be taken to make sure the correct OID is inserted in it.

- Remove SCO and Unixware ports (Tom Lane)

- Overhaul documentation build process (Alexander Lakhin)

- Use XSLT to build the PostgreSQL documentation (Peter Eisentraut)

  Previously Jade, DSSSL, and JadeTex were used.

- Build HTML documentation using XSLT stylesheets by default (Peter Eisentraut)

#### E.20.3.12. Additional Modules

- Allow file_fdw to read from program output as well as files (Corey Huinker, Adam Gomaa)

- In postgres_fdw, push aggregate functions to the remote server, when possible (Jeevan Chalke, Ashutosh Bapat)

  This reduces the amount of data that must be passed from the remote server, and offloads aggregate computation from the requesting server.

- In postgres_fdw, push joins to the remote server in more cases (David Rowley, Ashutosh Bapat, Etsuro Fujita)

- Properly support `OID` columns in postgres_fdw tables (Etsuro Fujita)

  Previously `OID` columns always returned zeros.

- Allow btree_gist and btree_gin to index enum types (Andrew Dunstan)

  This allows enums to be used in exclusion constraints.

- Add indexing support to btree_gist for the `UUID` data type (Paul Jungwirth)

- Add amcheck which can check the validity of B-tree indexes (Peter Geoghegan)

- Show ignored constants as `$N` rather than `?` in pg_stat_statements (Lukas Fittl)

- Improve cube's handling of zero-dimensional cubes (Tom Lane)

  This also improves handling of `infinite` and `NaN` values.

- Allow pg_buffercache to run with fewer locks (Ivan Kartyshov)

  This makes it less disruptive when run on production systems.

- Add pgstattuple function `pgstathashindex()` to view hash index statistics (Ashutosh Sharma)

- Use `GRANT` permissions to control pgstattuple function usage (Stephen Frost)

  This allows DBAs to allow non-superusers to run these functions.

- Reduce locking when pgstattuple examines hash indexes (Amit Kapila)

- Add pageinspect function `page_checksum()` to show a page's checksum (Tomas Vondra)

- Add pageinspect function `bt_page_items()` to print page items from a page image (Tomas Vondra)

- Add hash index support to pageinspect (Jesper Pedersen, Ashutosh Sharma)

### E.20.4. Acknowledgments

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

Adam Brightwell
Adam Brusselback
Adam Gomaa
Adam Sah
Adrian Klaver
Aidan Van Dyk
Aleksander Alekseev
Alexander Korotkov
Alexander Lakhin
Alexander Sosna
Alexey Bashtanov
Alexey Grishchenko
Alexey Isayko
Álvaro Hernández Tortosa
Álvaro Herrera
Amit Kapila
Amit Khandekar
Amit Langote
Amul Sul
Anastasia Lubennikova
Andreas Joseph Krogh
Andreas Karlsson
Andreas Scherbaum
Andreas Seltenreich
Andres Freund
Andrew Dunstan
Andrew Gierth
Andrew Wheelwright
Andrey Borodin
Andrey Lizenko
Andy Abelisto
Antonin Houska
Ants Aasma
Arjen Nienhuis
Arseny Sher
Artur Zakirov
Ashutosh Bapat
Ashutosh Sharma
Ashwin Agrawal
Atsushi Torikoshi
Ayumi Ishii
Basil Bourque
Beena Emerson
Ben de Graaff
Benedikt Grundmann
Bernd Helmle
Brad DeJong
Brandur Leach
Breen Hagan
Bruce Momjian
Bruno Wolff III
Catalin Iacob
Chapman Flack
Chen Huajun
Choi Doo-Won
Chris Bandy
Chris Richards
Chris Ruprecht
Christian Ullrich
Christoph Berg
Chuanting Wang
Claudio Freire
Clinton Adams
Const Zhang
Constantin Pan
Corey Huinker
Craig Ringer
Cynthia Shang
Dagfinn Ilmari Mannsåker
Daisuke Higuchi
Damian Quiroga
Dan Wood
Dang Minh Huong
Daniel Gustafsson
Daniel Vérité
Daniel Westermann
Daniele Varrazzo
Danylo Hlynskyi
Darko Prelec
Dave Cramer
Dave Page
David Christensen
David Fetter
David Johnston
David Rader
David Rowley
David Steele
Dean Rasheed
Denis Smirnov
Denish Patel
Dennis Björklund
Devrim Gündüz
Dilip Kumar
Dilyan Palauzov
Dima Pavlov
Dimitry Ivanov
Dmitriy Sarafannikov
Dmitry Dolgov
Dmitry Fedin
Don Morrison
Egor Rogov
Eiji Seki
Emil Iggland
Emre Hasegeli
Enrique Meneses
Erik Nordström
Erik Rijkers
Erwin Brandstetter
Etsuro Fujita
Eugen Konkov
Eugene Kazakov
Euler Taveira
Fabien Coelho
Fabrízio de Royes Mello
Feike Steenbergen
Felix Gerzaguet
Filip Jirsák
Fujii Masao
Gabriele Bartolini
Gabrielle Roth
Gao Zengqi
Gerdan Santos
Gianni Ciolli
Gilles Darold
Giuseppe Broccolo
Graham Dutton
Greg Atkins
Greg Burek
Grigory Smolkin
Guillaume Lelarge
Hans Buschmann
Haribabu Kommi
Heikki Linnakangas
Henry Boehlert
Huan Ruan
Ian Barwick
Igor Korot
Ildus Kurbangaliev
Ivan Kartyshov
Jaime Casanova
Jakob Egger
James Parks
Jarred Ward
Jason Li
Jason O'Donnell
Jason Petersen
Jeevan Chalke
Jeevan Ladhe
Jeff Dafoe
Jeff Davis
Jeff Janes
Jelte Fennema
Jeremy Finzel
Jeremy Schneider
Jeroen van der Ham
Jesper Pedersen
Jim Mlodgenski
Jim Nasby
Jinyu Zhang
Joe Conway
Joel Jacobson
John Harvey
Jon Nelson
Jordan Gigov
Josh Berkus
Josh Soref
Julian Markwort
Julien Rouhaud
Junseok Yang
Justin Muise
Justin Pryzby
Kacper Zuk
KaiGai Kohei
Karen Huddleston
Karl Lehenbauer
Karl O. Pinc
Keith Fiske
Kevin Grittner
Kim Rose Carlsen
Konstantin Evteev
Konstantin Knizhnik
Kuntal Ghosh
Kurt Kartaltepe
Kyle Conroy
Kyotaro Horiguchi
Laurenz Albe
Leonardo Cecchi
Ludovic Vaugeois-Pepin
Lukas Fittl
Magnus Hagander
Maksim Milyutin
Maksym Sobolyev
Marc Rassbach
Marc-Olaf Jaschke
Marcos Castedo
Marek Cvoren
Mark Dilger
Mark Kirkwood
Mark Pether
Marko Tiikkaja
Markus Winand
Marllius Ribeiro
Marti Raudsepp
Martín Marqués
Masahiko Sawada
Matheus Oliveira
Mathieu Fenniak
Merlin Moncure
Michael Banck
Michael Day
Michael Meskes
Michael Overmeyer
Michael Paquier
Mike Palmiotto
Milos Urbanek
Mithun Cy
Moshe Jacobson
Murtuza Zabuawala
Naoki Okano
Nathan Bossart
Nathan Wagner
Neha Khatri
Neha Sharma
Neil Anderson
Nicolas Baccelli
Nicolas Guini
Nicolas Thauvin
Nikhil Sontakke
Nikita Glukhov
Nikolaus Thiel
Nikolay Nikitin
Nikolay Shaplov
Noah Misch
Noriyoshi Shinoda
Olaf Gawenda
Oleg Bartunov
Oskari Saarenmaa
Otar Shavadze
Paresh More
Paul Jungwirth
Paul Ramsey
Pavan Deolasee
Pavel Golub
Pavel Hanák
Pavel Raiskup
Pavel Stehule
Peng Sun
Peter Eisentraut
Peter Geoghegan
Petr Jelínek
Philippe Beaudoin
Pierre-Emmanuel André
Piotr Stefaniak
Prabhat Sahu
QL Zhuo
Radek Slupik
Rafa de la Torre
Rafia Sabih
Ragnar Ouchterlony
Rahila Syed
Rajkumar Raghuwanshi
Regina Obe
Richard Pistole
Robert Haas
Robins Tharakan
Rod Taylor
Roman Shaposhnik
Rushabh Lathia
Ryan Murphy
Sandeep Thakkar
Scott Milliken
Sean Farrell
Sebastian Luque
Sehrope Sarkuni
Sergey Burladyan
Sergey Koposov
Shay Rojansky
Shinichi Matsuda
Sho Kato
Simon Riggs
Simone Gotti
Spencer Thomason
Stas Kelvich
Stepan Pesternikov
Stephen Frost
Steve Randall
Steve Singer
Steven Fackler
Steven Winfield
Suraj Kharage
Sveinn Sveinsson
Sven R. Kunze
Tahir Fakhroutdinov
Taiki Kondo
Takayuki Tsunakawa
Takeshi Ideriha
Tatsuo Ishii
Tatsuro Yamada
Teodor Sigaev
Thom Brown
Thomas Kellerer
Thomas Munro
Tim Goodaire
Tobias Bussmann
Tom Dunstan
Tom Lane
Tom van Tilburg
Tomas Vondra
Tomonari Katsumata
Tushar Ahuja
Vaishnavi Prabakaran
Venkata Balaji Nagothi
Vicky Vergara
Victor Wagner
Vik Fearing
Vinayak Pokale
Viren Negi
Vitaly Burovoy
Vladimir Kunshchikov
Vladimir Rusinov
Yi Wen Wong
Yugo Nagata
Zhen Ming Yang
Zhou Digoal

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