## E.156. Release 9.0

Release date: 2010-09-20

### E.156.1. Overview

This release of PostgreSQL adds features that have been requested for years, such as easy-to-use replication, a mass permission-changing facility, and anonymous code blocks. While past major releases have been conservative in their scope, this release shows a bold new desire to provide facilities that new and existing users of PostgreSQL will embrace. This has all been done with few incompatibilities. Major enhancements include:

- Built-in replication based on log shipping. This advance consists of two features: Streaming Replication, allowing continuous archive (WAL) files to be streamed over a network connection to a standby server, and Hot Standby, allowing continuous archive standby servers to execute read-only queries. The net effect is to support a single master with multiple read-only slave servers.

- Easier database object permissions management. `GRANT`/`REVOKE IN SCHEMA` supports mass permissions changes on existing objects, while `ALTER DEFAULT PRIVILEGES` allows control of privileges for objects created in the future. Large objects (BLOBs) now support permissions management as well.

- Broadly enhanced stored procedure support. The `DO` statement supports ad-hoc or “anonymous” code blocks. Functions can now be called using named parameters. PL/pgSQL is now installed by default, and PL/Perl and PL/Python have been enhanced in several ways, including support for Python3.

- Full support for 64-bit Windows.

- More advanced reporting queries, including additional windowing options (`PRECEDING` and `FOLLOWING`) and the ability to control the order in which values are fed to aggregate functions.

- New trigger features, including SQL-standard-compliant per-column triggers and conditional trigger execution.

- Deferrable unique constraints. Mass updates to unique keys are now possible without trickery.

- Exclusion constraints. These provide a generalized version of unique constraints, allowing enforcement of complex conditions.

- New and enhanced security features, including RADIUS authentication, LDAP authentication improvements, and a new contrib module `passwordcheck` for testing password strength.

- New high-performance implementation of the `LISTEN`/`NOTIFY` feature. Pending events are now stored in a memory-based queue rather than a table. Also, a “payload” string can be sent with each event, rather than transmitting just an event name as before.

- New implementation of `VACUUM FULL`. This command now rewrites the entire table and indexes, rather than moving individual rows to compact space. It is substantially faster in most cases, and no longer results in index bloat.

- New contrib module `pg_upgrade` to support in-place upgrades from 8.3 or 8.4 to 9.0.

- Multiple performance enhancements for specific types of queries, including elimination of unnecessary joins. This helps optimize some automatically-generated queries, such as those produced by object-relational mappers (ORMs).

- `EXPLAIN` enhancements. The output is now available in JSON, XML, or YAML format, and includes buffer utilization and other data not previously available.

- `hstore` improvements, including new functions and greater data capacity.

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

### E.156.2. Migration to Version 9.0

A dump/restore using pg_dump, or use of pg_upgrade, is required for those wishing to migrate data from any previous release.

Version 9.0 contains a number of changes that selectively break backwards compatibility in order to support new features and code quality improvements. In particular, users who make extensive use of PL/pgSQL, Point-In-Time Recovery (PITR), or Warm Standby should test their applications because of slight user-visible changes in those areas. Observe the following incompatibilities:

#### E.156.2.1. Server Settings

- Remove server parameter `add_missing_from`, which was defaulted to off for many years (Tom Lane)

- Remove server parameter `regex_flavor`, which was defaulted to `advanced` for many years (Tom Lane)

- `archive_mode` now only affects `archive_command`; a new setting, `wal_level`, affects the contents of the write-ahead log (Heikki Linnakangas)

- `log_temp_files` now uses default file size units of kilobytes (Robert Haas)

#### E.156.2.2. Queries

- When querying a parent table, do not do any separate permission checks on child tables scanned as part of the query (Peter Eisentraut)

  The SQL standard specifies this behavior, and it is also much more convenient in practice than the former behavior of checking permissions on each child as well as the parent.

#### E.156.2.3. Data Types

- `bytea` output now appears in hex format by default (Peter Eisentraut)

  The server parameter `bytea_output` can be used to select the traditional output format if needed for compatibility.

- Array input now considers only plain ASCII whitespace characters to be potentially ignorable; it will never ignore non-ASCII characters, even if they are whitespace according to some locales (Tom Lane)

  This avoids some corner cases where array values could be interpreted differently depending on the server's locale settings.

- Improve standards compliance of `SIMILAR TO` patterns and SQL-style `substring()` patterns (Tom Lane)

  This includes treating `?` and `{...}` as pattern metacharacters, while they were simple literal characters before; that corresponds to new features added in SQL:2008. Also, `^` and `$` are now treated as simple literal characters; formerly they were treated as metacharacters, as if the pattern were following POSIX rather than SQL rules. Also, in SQL-standard `substring()`, use of parentheses for nesting no longer interferes with capturing of a substring. Also, processing of bracket expressions (character classes) is now more standards-compliant.

- Reject negative length values in 3-parameter `substring()` for bit strings, per the SQL standard (Tom Lane)

- Make `date_trunc` truncate rather than round when reducing precision of fractional seconds (Tom Lane)

  The code always acted this way for integer-based dates/times. Now float-based dates/times behave similarly.

#### E.156.2.4. Object Renaming

- Tighten enforcement of column name consistency during `RENAME` when a child table inherits the same column from multiple unrelated parents (KaiGai Kohei)

- No longer automatically rename indexes and index columns when the underlying table columns are renamed (Tom Lane)

  Administrators can still rename such indexes and columns manually. This change will require an update of the JDBC driver, and possibly other drivers, so that unique indexes are correctly recognized after a rename.

- `CREATE OR REPLACE FUNCTION` can no longer change the declared names of function parameters (Pavel Stehule)

  In order to avoid creating ambiguity in named-parameter calls, it is no longer allowed to change the aliases for input parameters in the declaration of an existing function (although names can still be assigned to previously unnamed parameters). You now have to `DROP` and recreate the function to do that.

#### E.156.2.5. PL/pgSQL

- PL/pgSQL now throws an error if a variable name conflicts with a column name used in a query (Tom Lane)

  The former behavior was to bind ambiguous names to PL/pgSQL variables in preference to query columns, which often resulted in surprising misbehavior. Throwing an error allows easy detection of ambiguous situations. Although it's recommended that functions encountering this type of error be modified to remove the conflict, the old behavior can be restored if necessary via the configuration parameter `plpgsql.variable_conflict`, or via the per-function option `#variable_conflict`.

- PL/pgSQL no longer allows variable names that match certain SQL reserved words (Tom Lane)

  This is a consequence of aligning the PL/pgSQL parser to match the core SQL parser more closely. If necessary, variable names can be double-quoted to avoid this restriction.

- PL/pgSQL now requires columns of composite results to match the expected type modifier as well as base type (Pavel Stehule, Tom Lane)

  For example, if a column of the result type is declared as `NUMERIC(30,2)`, it is no longer acceptable to return a `NUMERIC` of some other precision in that column. Previous versions neglected to check the type modifier and would thus allow result rows that didn't actually conform to the declared restrictions.

- PL/pgSQL now treats selection into composite fields more consistently (Tom Lane)

  Formerly, a statement like `SELECT ... INTO `rec`.`fld` FROM ...` was treated as a scalar assignment even if the record field `fld` was of composite type. Now it is treated as a record assignment, the same as when the `INTO` target is a regular variable of composite type. So the values to be assigned to the field's subfields should be written as separate columns of the `SELECT` list, not as a `ROW(...)` construct as in previous versions.

  If you need to do this in a way that will work in both 9.0 and previous releases, you can write something like ``rec`.`fld` := ROW(...) FROM ...`.

- Remove PL/pgSQL's `RENAME` declaration (Tom Lane)

  Instead of `RENAME`, use `ALIAS`, which can now create an alias for any variable, not only dollar sign parameter names (such as `$1`) as before.

#### E.156.2.6. Other Incompatibilities

- Deprecate use of `=>` as an operator name (Robert Haas)

  Future versions of PostgreSQL will probably reject this operator name entirely, in order to support the SQL-standard notation for named function parameters. For the moment, it is still allowed, but a warning is emitted when such an operator is defined.

- Remove support for platforms that don't have a working 64-bit integer data type (Tom Lane)

  It is believed all still-supported platforms have working 64-bit integer data types.

### E.156.3. Changes

Version 9.0 has an unprecedented number of new major features, and over 200 enhancements, improvements, new commands, new functions, and other changes.

#### E.156.3.1. Server

##### E.156.3.1.1. Continuous Archiving and Streaming Replication

PostgreSQL's existing standby-server capability has been expanded both to support read-only queries on standby servers and to greatly reduce the lag between master and standby servers. For many users, this will be a useful and low-administration form of replication, either for high availability or for horizontal scalability.

- Allow a standby server to accept read-only queries (Simon Riggs, Heikki Linnakangas)

  This feature is called Hot Standby. There are new `postgresql.conf` and `recovery.conf` settings to control this feature, as well as extensive documentation.

- Allow write-ahead log (WAL) data to be streamed to a standby server (Fujii Masao, Heikki Linnakangas)

  This feature is called Streaming Replication. Previously WAL data could be sent to standby servers only in units of entire WAL files (normally 16 megabytes each). Streaming Replication eliminates this inefficiency and allows updates on the master to be propagated to standby servers with very little delay. There are new `postgresql.conf` and `recovery.conf` settings to control this feature, as well as extensive documentation.

- Add `pg_last_xlog_receive_location()` and `pg_last_xlog_replay_location()`, which can be used to monitor standby server WAL activity (Simon Riggs, Fujii Masao, Heikki Linnakangas)

##### E.156.3.1.2. Performance

- Allow per-tablespace values to be set for sequential and random page cost estimates (`seq_page_cost`/`random_page_cost`) via `ALTER TABLESPACE ... SET/RESET` (Robert Haas)

- Improve performance and reliability of EvalPlanQual rechecks in join queries (Tom Lane)

  `UPDATE`, `DELETE`, and `SELECT FOR UPDATE/SHARE` queries that involve joins will now behave much better when encountering freshly-updated rows.

- Improve performance of `TRUNCATE` when the table was created or truncated earlier in the same transaction (Tom Lane)

- Improve performance of finding inheritance child tables (Tom Lane)

##### E.156.3.1.3. Optimizer

- Remove unnecessary outer joins (Robert Haas)

  Outer joins where the inner side is unique and not referenced above the join are unnecessary and are therefore now removed. This will accelerate many automatically generated queries, such as those created by object-relational mappers (ORMs).

- Allow `IS NOT NULL` restrictions to use indexes (Tom Lane)

  This is particularly useful for finding `MAX()`/`MIN()` values in indexes that contain many null values.

- Improve the optimizer's choices about when to use materialize nodes, and when to use sorting versus hashing for `DISTINCT` (Tom Lane)

- Improve the optimizer's equivalence detection for expressions involving `boolean` `<>` operators (Tom Lane)

##### E.156.3.1.4. GEQO

- Use the same random seed every time GEQO plans a query (Andres Freund)

  While the Genetic Query Optimizer (GEQO) still selects random plans, it now always selects the same random plans for identical queries, thus giving more consistent performance. You can modify `geqo_seed` to experiment with alternative plans.

- Improve GEQO plan selection (Tom Lane)

  This avoids the rare error “failed to make a valid plan”, and should also improve planning speed.

##### E.156.3.1.5. Optimizer Statistics

- Improve `ANALYZE` to support inheritance-tree statistics (Tom Lane)

  This is particularly useful for partitioned tables. However, autovacuum does not yet automatically re-analyze parent tables when child tables change.

- Improve autovacuum's detection of when re-analyze is necessary (Tom Lane)

- Improve optimizer's estimation for greater/less-than comparisons (Tom Lane)

  When looking up statistics for greater/less-than comparisons, if the comparison value is in the first or last histogram bucket, use an index (if available) to fetch the current actual column minimum or maximum. This greatly improves the accuracy of estimates for comparison values near the ends of the data range, particularly if the range is constantly changing due to addition of new data.

- Allow setting of number-of-distinct-values statistics using `ALTER TABLE` (Robert Haas)

  This allows users to override the estimated number or percentage of distinct values for a column. This statistic is normally computed by `ANALYZE`, but the estimate can be poor, especially on tables with very large numbers of rows.

##### E.156.3.1.6. Authentication

- Add support for RADIUS (Remote Authentication Dial In User Service) authentication (Magnus Hagander)

- Allow LDAP (Lightweight Directory Access Protocol) authentication to operate in “search/bind” mode (Robert Fleming, Magnus Hagander)

  This allows the user to be looked up first, then the system uses the DN (Distinguished Name) returned for that user.

- Add `samehost` and `samenet` designations to `pg_hba.conf` (Stef Walter)

  These match the server's IP address and subnet address respectively.

- Pass trusted SSL root certificate names to the client so the client can return an appropriate client certificate (Craig Ringer)

##### E.156.3.1.7. Monitoring

- Add the ability for clients to set an application name, which is displayed in `pg_stat_activity` (Dave Page)

  This allows administrators to characterize database traffic and troubleshoot problems by source application.

- Add a SQLSTATE option (`%e`) to `log_line_prefix` (Guillaume Smet)

  This allows users to compile statistics on errors and messages by error code number.

- Write to the Windows event log in UTF16 encoding (Itagaki Takahiro)

  Now there is true multilingual support for PostgreSQL log messages on Windows.

##### E.156.3.1.8. Statistics Counters

- Add `pg_stat_reset_shared('bgwriter')` to reset the cluster-wide shared statistics for the background writer (Greg Smith)

- Add `pg_stat_reset_single_table_counters()` and `pg_stat_reset_single_function_counters()` to allow resetting the statistics counters for individual tables and functions (Magnus Hagander)

##### E.156.3.1.9. Server Settings

- Allow setting of configuration parameters based on database/role combinations (Alvaro Herrera)

  Previously only per-database and per-role settings were possible, not combinations. All role and database settings are now stored in the new `pg_db_role_setting` system catalog. A new psql command `\drds` shows these settings. The legacy system views `pg_roles`, `pg_shadow`, and `pg_user` do not show combination settings, and therefore no longer completely represent the configuration for a user or database.

- Add server parameter `bonjour`, which controls whether a Bonjour-enabled server advertises itself via Bonjour (Tom Lane)

  The default is off, meaning it does not advertise. This allows packagers to distribute Bonjour-enabled builds without worrying that individual users might not want the feature.

- Add server parameter `enable_material`, which controls the use of materialize nodes in the optimizer (Robert Haas)

  The default is on. When off, the optimizer will not add materialize nodes purely for performance reasons, though they will still be used when necessary for correctness.

- Change server parameter `log_temp_files` to use default file size units of kilobytes (Robert Haas)

  Previously this setting was interpreted in bytes if no units were specified.

- Log changes of parameter values when `postgresql.conf` is reloaded (Peter Eisentraut)

  This lets administrators and security staff audit changes of database settings, and is also very convenient for checking the effects of `postgresql.conf` edits.

- Properly enforce superuser permissions for custom server parameters (Tom Lane)

  Non-superusers can no longer issue `ALTER ROLE`/`DATABASE SET` for parameters that are not currently known to the server. This allows the server to correctly check that superuser-only parameters are only set by superusers. Previously, the `SET` would be allowed and then ignored at session start, making superuser-only custom parameters much less useful than they should be.

#### E.156.3.2. Queries

- Perform `SELECT FOR UPDATE`/`SHARE` processing after applying `LIMIT`, so the number of rows returned is always predictable (Tom Lane)

  Previously, changes made by concurrent transactions could cause a `SELECT FOR UPDATE` to unexpectedly return fewer rows than specified by its `LIMIT`. `FOR UPDATE` in combination with `ORDER BY` can still produce surprising results, but that can be corrected by placing `FOR UPDATE` in a subquery.

- Allow mixing of traditional and SQL-standard `LIMIT`/`OFFSET` syntax (Tom Lane)

- Extend the supported frame options in window functions (Hitoshi Harada)

  Frames can now start with `CURRENT ROW`, and the `ROWS `n` PRECEDING`/`FOLLOWING` options are now supported.

- Make `SELECT INTO` and `CREATE TABLE AS` return row counts to the client in their command tags (Boszormenyi Zoltan)

  This can save an entire round-trip to the client, allowing result counts and pagination to be calculated without an additional `COUNT` query.

##### E.156.3.2.1. Unicode Strings

- Support Unicode surrogate pairs (dual 16-bit representation) in `U&` strings and identifiers (Peter Eisentraut)

- Support Unicode escapes in `E'...'` strings (Marko Kreen)

#### E.156.3.3. Object Manipulation

- Speed up `CREATE DATABASE` by deferring flushes to disk (Andres Freund, Greg Stark)

- Allow comments on columns of tables, views, and composite types only, not other relation types such as indexes and TOAST tables (Tom Lane)

- Allow the creation of enumerated types containing no values (Bruce Momjian)

- Let values of columns having storage type `MAIN` remain on the main heap page unless the row cannot fit on a page (Kevin Grittner)

  Previously `MAIN` values were forced out to TOAST tables until the row size was less than one-quarter of the page size.

##### E.156.3.3.1. `ALTER TABLE`

- Implement `IF EXISTS` for `ALTER TABLE DROP COLUMN` and `ALTER TABLE DROP CONSTRAINT` (Andres Freund)

- Allow `ALTER TABLE` commands that rewrite tables to skip WAL logging (Itagaki Takahiro)

  Such operations either produce a new copy of the table or are rolled back, so WAL archiving can be skipped, unless running in continuous archiving mode. This reduces I/O overhead and improves performance.

- Fix failure of `ALTER TABLE `table` ADD COLUMN `col` serial` when done by non-owner of table (Tom Lane)

##### E.156.3.3.2. `CREATE TABLE`

- Add support for copying `COMMENTS` and `STORAGE` settings in `CREATE TABLE ... LIKE` commands (Itagaki Takahiro)

- Add a shortcut for copying all properties in `CREATE TABLE ... LIKE` commands (Itagaki Takahiro)

- Add the SQL-standard `CREATE TABLE ... OF `type`` command (Peter Eisentraut)

  This allows creation of a table that matches an existing composite type. Additional constraints and defaults can be specified in the command.

##### E.156.3.3.3. Constraints

- Add deferrable unique constraints (Dean Rasheed)

  This allows mass updates, such as `UPDATE tab SET col = col + 1`, to work reliably on columns that have unique indexes or are marked as primary keys. If the constraint is specified as `DEFERRABLE` it will be checked at the end of the statement, rather than after each row is updated. The constraint check can also be deferred until the end of the current transaction, allowing such updates to be spread over multiple SQL commands.

- Add exclusion constraints (Jeff Davis)

  Exclusion constraints generalize uniqueness constraints by allowing arbitrary comparison operators, not just equality. They are created with the `CREATE TABLE CONSTRAINT ... EXCLUDE` clause. The most common use of exclusion constraints is to specify that column entries must not overlap, rather than simply not be equal. This is useful for time periods and other ranges, as well as arrays. This feature enhances checking of data integrity for many calendaring, time-management, and scientific applications.

- Improve uniqueness-constraint violation error messages to report the values causing the failure (Itagaki Takahiro)

  For example, a uniqueness constraint violation might now report `Key (x)=(2) already exists`.

##### E.156.3.3.4. Object Permissions

- Add the ability to make mass permission changes across a whole schema using the new `GRANT`/`REVOKE IN SCHEMA` clause (Petr Jelinek)

  This simplifies management of object permissions and makes it easier to utilize database roles for application data security.

- Add `ALTER DEFAULT PRIVILEGES` command to control privileges of objects created later (Petr Jelinek)

  This greatly simplifies the assignment of object privileges in a complex database application. Default privileges can be set for tables, views, sequences, and functions. Defaults may be assigned on a per-schema basis, or database-wide.

- Add the ability to control large object (BLOB) permissions with `GRANT`/`REVOKE` (KaiGai Kohei)

  Formerly, any database user could read or modify any large object. Read and write permissions can now be granted and revoked per large object, and the ownership of large objects is tracked.

#### E.156.3.4. Utility Operations

- Make `LISTEN`/`NOTIFY` store pending events in a memory queue, rather than in a system table (Joachim Wieland)

  This substantially improves performance, while retaining the existing features of transactional support and guaranteed delivery.

- Allow `NOTIFY` to pass an optional “payload” string to listeners (Joachim Wieland)

  This greatly improves the usefulness of `LISTEN`/`NOTIFY` as a general-purpose event queue system.

- Allow `CLUSTER` on all per-database system catalogs (Tom Lane)

  Shared catalogs still cannot be clustered.

##### E.156.3.4.1. `COPY`

- Accept `COPY ... CSV FORCE QUOTE *` (Itagaki Takahiro)

  Now `*` can be used as shorthand for “all columns” in the `FORCE QUOTE` clause.

- Add new `COPY` syntax that allows options to be specified inside parentheses (Robert Haas, Emmanuel Cecchet)

  This allows greater flexibility for future `COPY` options. The old syntax is still supported, but only for pre-existing options.

##### E.156.3.4.2. `EXPLAIN`

- Allow `EXPLAIN` to output in XML, JSON, or YAML format (Robert Haas, Greg Sabino Mullane)

  The new output formats are easily machine-readable, supporting the development of new tools for analysis of `EXPLAIN` output.

- Add new `BUFFERS` option to report query buffer usage during `EXPLAIN ANALYZE` (Itagaki Takahiro)

  This allows better query profiling for individual queries. Buffer usage is no longer reported in the output for log_statement_stats and related settings.

- Add hash usage information to `EXPLAIN` output (Robert Haas)

- Add new `EXPLAIN` syntax that allows options to be specified inside parentheses (Robert Haas)

  This allows greater flexibility for future `EXPLAIN` options. The old syntax is still supported, but only for pre-existing options.

##### E.156.3.4.3. `VACUUM`

- Change `VACUUM FULL` to rewrite the entire table and rebuild its indexes, rather than moving individual rows around to compact space (Itagaki Takahiro, Tom Lane)

  The previous method was usually slower and caused index bloat. Note that the new method will use more disk space transiently during `VACUUM FULL`; potentially as much as twice the space normally occupied by the table and its indexes.

- Add new `VACUUM` syntax that allows options to be specified inside parentheses (Itagaki Takahiro)

  This allows greater flexibility for future `VACUUM` options. The old syntax is still supported, but only for pre-existing options.

##### E.156.3.4.4. Indexes

- Allow an index to be named automatically by omitting the index name in `CREATE INDEX` (Tom Lane)

- By default, multicolumn indexes are now named after all their columns; and index expression columns are now named based on their expressions (Tom Lane)

- Reindexing shared system catalogs is now fully transactional and crash-safe (Tom Lane)

  Formerly, reindexing a shared index was only allowed in standalone mode, and a crash during the operation could leave the index in worse condition than it was before.

- Add `point_ops` operator class for GiST (Teodor Sigaev)

  This feature permits GiST indexing of `point` columns. The index can be used for several types of queries such as `point` `<@` `polygon` (point is in polygon). This should make many PostGIS queries faster.

- Use red-black binary trees for GIN index creation (Teodor Sigaev)

  Red-black trees are self-balancing. This avoids slowdowns in cases where the input is in nonrandom order.

#### E.156.3.5. Data Types

- Allow `bytea` values to be written in hex notation (Peter Eisentraut)

  The server parameter `bytea_output` controls whether hex or traditional format is used for `bytea` output. Libpq's `PQescapeByteaConn()` function automatically uses the hex format when connected to PostgreSQL 9.0 or newer servers. However, pre-9.0 libpq versions will not correctly process hex format from newer servers.

  The new hex format will be directly compatible with more applications that use binary data, allowing them to store and retrieve it without extra conversion. It is also significantly faster to read and write than the traditional format.

- Allow server parameter extra_float_digits to be increased to `3` (Tom Lane)

  The previous maximum `extra_float_digits` setting was `2`. There are cases where 3 digits are needed to dump and restore `float4` values exactly. pg_dump will now use the setting of 3 when dumping from a server that allows it.

- Tighten input checking for `int2vector` values (Caleb Welton)

##### E.156.3.5.1. Full Text Search

- Add prefix support in `synonym` dictionaries (Teodor Sigaev)

- Add filtering dictionaries (Teodor Sigaev)

  Filtering dictionaries allow tokens to be modified then passed to subsequent dictionaries.

- Allow underscores in email-address tokens (Teodor Sigaev)

- Use more standards-compliant rules for parsing URL tokens (Tom Lane)

#### E.156.3.6. Functions

- Allow function calls to supply parameter names and match them to named parameters in the function definition (Pavel Stehule)

  For example, if a function is defined to take parameters `a` and `b`, it can be called with `func(a := 7, b := 12)` or `func(b := 12, a := 7)`.

- Support locale-specific regular expression processing with UTF-8 server encoding (Tom Lane)

  Locale-specific regular expression functionality includes case-insensitive matching and locale-specific character classes. Previously, these features worked correctly for non-ASCII characters only if the database used a single-byte server encoding (such as LATIN1). They will still misbehave in multi-byte encodings other than UTF-8.

- Add support for scientific notation in `to_char()` (`EEEE` specification) (Pavel Stehule, Brendan Jurd)

- Make `to_char()` honor `FM` (fill mode) in `Y`, `YY`, and `YYY` specifications (Bruce Momjian, Tom Lane)

  It was already honored by `YYYY`.

- Fix `to_char()` to output localized numeric and monetary strings in the correct encoding on Windows (Hiroshi Inoue, Itagaki Takahiro, Bruce Momjian)

- Correct calculations of “overlaps” and “contains” operations for polygons (Teodor Sigaev)

  The polygon `&&` (overlaps) operator formerly just checked to see if the two polygons' bounding boxes overlapped. It now does a more correct check. The polygon `@>` and `<@` (contains/contained by) operators formerly checked to see if one polygon's vertexes were all contained in the other; this can wrongly report “true” for some non-convex polygons. Now they check that all line segments of one polygon are contained in the other.

##### E.156.3.6.1. Aggregates

- Allow aggregate functions to use `ORDER BY` (Andrew Gierth)

  For example, this is now supported: `array_agg(a ORDER BY b)`. This is useful with aggregates for which the order of input values is significant, and eliminates the need to use a nonstandard subquery to determine the ordering.

- Multi-argument aggregate functions can now use `DISTINCT` (Andrew Gierth)

- Add the `string_agg()` aggregate function to combine values into a single string (Pavel Stehule)

- Aggregate functions that are called with `DISTINCT` are now passed NULL values if the aggregate transition function is not marked as `STRICT` (Andrew Gierth)

  For example, `agg(DISTINCT x)` might pass a NULL `x` value to `agg()`. This is more consistent with the behavior in non-`DISTINCT` cases.

##### E.156.3.6.2. Bit Strings

- Add `get_bit()` and `set_bit()` functions for `bit` strings, mirroring those for `bytea` (Leonardo F)

- Implement `OVERLAY()` (replace) for `bit` strings and `bytea` (Leonardo F)

##### E.156.3.6.3. Object Information Functions

- Add `pg_table_size()` and `pg_indexes_size()` to provide a more user-friendly interface to the `pg_relation_size()` function (Bernd Helmle)

- Add `has_sequence_privilege()` for sequence permission checking (Abhijit Menon-Sen)

- Update the information_schema views to conform to SQL:2008 (Peter Eisentraut)

- Make the `information_schema` views correctly display maximum octet lengths for `char` and `varchar` columns (Peter Eisentraut)

- Speed up `information_schema` privilege views (Joachim Wieland)

##### E.156.3.6.4. Function and Trigger Creation

- Support execution of anonymous code blocks using the `DO` statement (Petr Jelinek, Joshua Tolley, Hannu Valtonen)

  This allows execution of server-side code without the need to create and delete a temporary function definition. Code can be executed in any language for which the user has permissions to define a function.

- Implement SQL-standard-compliant per-column triggers (Itagaki Takahiro)

  Such triggers are fired only when the specified column(s) are affected by the query, e.g. appear in an `UPDATE`'s `SET` list.

- Add the `WHEN` clause to `CREATE TRIGGER` to allow control over whether a trigger is fired (Itagaki Takahiro)

  While the same type of check can always be performed inside the trigger, doing it in an external `WHEN` clause can have performance benefits.

#### E.156.3.7. Server-Side Languages

- Add the `OR REPLACE` clause to `CREATE LANGUAGE` (Tom Lane)

  This is helpful to optionally install a language if it does not already exist, and is particularly helpful now that PL/pgSQL is installed by default.

##### E.156.3.7.1. PL/pgSQL Server-Side Language

- Install PL/pgSQL by default (Bruce Momjian)

  The language can still be removed from a particular database if the administrator has security or performance concerns about making it available.

- Improve handling of cases where PL/pgSQL variable names conflict with identifiers used in queries within a function (Tom Lane)

  The default behavior is now to throw an error when there is a conflict, so as to avoid surprising behaviors. This can be modified, via the configuration parameter `plpgsql.variable_conflict` or the per-function option `#variable_conflict`, to allow either the variable or the query-supplied column to be used. In any case PL/pgSQL will no longer attempt to substitute variables in places where they would not be syntactically valid.

- Make PL/pgSQL use the main lexer, rather than its own version (Tom Lane)

  This ensures accurate tracking of the main system's behavior for details such as string escaping. Some user-visible details, such as the set of keywords considered reserved in PL/pgSQL, have changed in consequence.

- Avoid throwing an unnecessary error for an invalid record reference (Tom Lane)

  An error is now thrown only if the reference is actually fetched, rather than whenever the enclosing expression is reached. For example, many people have tried to do this in triggers:

      if TG_OP = 'INSERT' and NEW.col1 = ... then

  This will now actually work as expected.

- Improve PL/pgSQL's ability to handle row types with dropped columns (Pavel Stehule)

- Allow input parameters to be assigned values within PL/pgSQL functions (Steve Prentice)

  Formerly, input parameters were treated as being declared `CONST`, so the function's code could not change their values. This restriction has been removed to simplify porting of functions from other DBMSes that do not impose the equivalent restriction. An input parameter now acts like a local variable initialized to the passed-in value.

- Improve error location reporting in PL/pgSQL (Tom Lane)

- Add `count` and `ALL` options to `MOVE FORWARD`/`BACKWARD` in PL/pgSQL (Pavel Stehule)

- Allow PL/pgSQL's `WHERE CURRENT OF` to use a cursor variable (Tom Lane)

- Allow PL/pgSQL's `OPEN `cursor` FOR EXECUTE` to use parameters (Pavel Stehule, Itagaki Takahiro)

  This is accomplished with a new `USING` clause.

##### E.156.3.7.2. PL/Perl Server-Side Language

- Add new PL/Perl functions: `quote_literal()`, `quote_nullable()`, `quote_ident()`, `encode_bytea()`, `decode_bytea()`, `looks_like_number()`, `encode_array_literal()`, `encode_array_constructor()` (Tim Bunce)

- Add server parameter `plperl.on_init` to specify a PL/Perl initialization function (Tim Bunce)

  `plperl.on_plperl_init` and `plperl.on_plperlu_init` are also available for initialization that is specific to the trusted or untrusted language respectively.

- Support `END` blocks in PL/Perl (Tim Bunce)

  `END` blocks do not currently allow database access.

- Allow `use strict` in PL/Perl (Tim Bunce)

  Perl `strict` checks can also be globally enabled with the new server parameter `plperl.use_strict`.

- Allow `require` in PL/Perl (Tim Bunce)

  This basically tests to see if the module is loaded, and if not, generates an error. It will not allow loading of modules that the administrator has not preloaded via the initialization parameters.

- Allow `use feature` in PL/Perl if Perl version 5.10 or later is used (Tim Bunce)

- Verify that PL/Perl return values are valid in the server encoding (Andrew Dunstan)

##### E.156.3.7.3. PL/Python Server-Side Language

- Add Unicode support in PL/Python (Peter Eisentraut)

  Strings are automatically converted from/to the server encoding as necessary.

- Improve `bytea` support in PL/Python (Caleb Welton)

  `Bytea` values passed into PL/Python are now represented as binary, rather than the PostgreSQL `bytea` text format. `Bytea` values containing null bytes are now also output properly from PL/Python. Passing of boolean, integer, and float values was also improved.

- Support arrays as parameters and return values in PL/Python (Peter Eisentraut)

- Improve mapping of SQL domains to Python types (Peter Eisentraut)

- Add Python 3 support to PL/Python (Peter Eisentraut)

  The new server-side language is called `plpython3u`. This cannot be used in the same session with the Python 2 server-side language.

- Improve error location and exception reporting in PL/Python (Peter Eisentraut)

#### E.156.3.8. Client Applications

- Add an `--analyze-only` option to `vacuumdb`, to analyze without vacuuming (Bruce Momjian)

##### E.156.3.8.1. psql

- Add support for quoting/escaping the values of psql variables as SQL strings or identifiers (Pavel Stehule, Robert Haas)

  For example, `:'var'` will produce the value of `var` quoted and properly escaped as a literal string, while `:"var"` will produce its value quoted and escaped as an identifier.

- Ignore a leading UTF-8-encoded Unicode byte-order marker in script files read by psql (Itagaki Takahiro)

  This is enabled when the client encoding is UTF-8. It improves compatibility with certain editors, mostly on Windows, that insist on inserting such markers.

- Fix `psql --file -` to properly honor `--single-transaction` (Bruce Momjian)

- Avoid overwriting of psql's command-line history when two psql sessions are run concurrently (Tom Lane)

- Improve psql's tab completion support (Itagaki Takahiro)

- Show `\timing` output when it is enabled, regardless of “quiet” mode (Peter Eisentraut)

###### E.156.3.8.1.1. psql Display

- Improve display of wrapped columns in psql (Roger Leigh)

  This behavior is now the default. The previous formatting is available by using `\pset linestyle old-ascii`.

- Allow psql to use fancy Unicode line-drawing characters via `\pset linestyle unicode` (Roger Leigh)

###### E.156.3.8.1.2. psql `\d` Commands

- Make `\d` show child tables that inherit from the specified parent (Damien Clochard)

  `\d` shows only the number of child tables, while `\d+` shows the names of all child tables.

- Show definitions of index columns in `\d index_name` (Khee Chin)

  The definition is useful for expression indexes.

- Show a view's defining query only in `\d+`, not in `\d` (Peter Eisentraut)

  Always including the query was deemed overly verbose.

##### E.156.3.8.2. pg_dump

- Make pg_dump/pg_restore `--clean` also remove large objects (Itagaki Takahiro)

- Fix pg_dump to properly dump large objects when `standard_conforming_strings` is enabled (Tom Lane)

  The previous coding could fail when dumping to an archive file and then generating script output from pg_restore.

- pg_restore now emits large-object data in hex format when generating script output (Tom Lane)

  This could cause compatibility problems if the script is then loaded into a pre-9.0 server. To work around that, restore directly to the server, instead.

- Allow pg_dump to dump comments attached to columns of composite types (Taro Minowa (Higepon))

- Make pg_dump `--verbose` output the pg_dump and server versions in text output mode (Jim Cox, Tom Lane)

  These were already provided in custom output mode.

- pg_restore now complains if any command-line arguments remain after the switches and optional file name (Tom Lane)

  Previously, it silently ignored any such arguments.

##### E.156.3.8.3. pg_ctl

- Allow pg_ctl to be used safely to start the postmaster during a system reboot (Tom Lane)

  Previously, pg_ctl's parent process could have been mistakenly identified as a running postmaster based on a stale postmaster lock file, resulting in a transient failure to start the database.

- Give pg_ctl the ability to initialize the database (by invoking initdb) (Zdenek Kotala)

#### E.156.3.9. Development Tools

##### E.156.3.9.1. libpq

- Add new libpq functions `PQconnectdbParams()` and `PQconnectStartParams()` (Guillaume Lelarge)

  These functions are similar to `PQconnectdb()` and `PQconnectStart()` except that they accept a null-terminated array of connection options, rather than requiring all options to be provided in a single string.

- Add libpq functions `PQescapeLiteral()` and `PQescapeIdentifier()` (Robert Haas)

  These functions return appropriately quoted and escaped SQL string literals and identifiers. The caller is not required to pre-allocate the string result, as is required by `PQescapeStringConn()`.

- Add support for a per-user service file (`.pg_service.conf`), which is checked before the site-wide service file (Peter Eisentraut)

- Properly report an error if the specified libpq service cannot be found (Peter Eisentraut)

- Add TCP keepalive settings in libpq (Tollef Fog Heen, Fujii Masao, Robert Haas)

  Keepalive settings were already supported on the server end of TCP connections.

- Avoid extra system calls to block and unblock `SIGPIPE` in libpq, on platforms that offer alternative methods (Jeremy Kerr)

- When a `.pgpass`-supplied password fails, mention where the password came from in the error message (Bruce Momjian)

- Load all SSL certificates given in the client certificate file (Tom Lane)

  This improves support for indirectly-signed SSL certificates.

##### E.156.3.9.2. ecpg

- Add SQLDA (SQL Descriptor Area) support to ecpg (Boszormenyi Zoltan)

- Add the `DESCRIBE` [ `OUTPUT` ] statement to ecpg (Boszormenyi Zoltan)

- Add an ECPGtransactionStatus function to return the current transaction status (Bernd Helmle)

- Add the `string` data type in ecpg Informix-compatibility mode (Boszormenyi Zoltan)

- Allow ecpg to use `new` and `old` variable names without restriction (Michael Meskes)

- Allow ecpg to use variable names in `free()` (Michael Meskes)

- Make `ecpg_dynamic_type()` return zero for non-SQL3 data types (Michael Meskes)

  Previously it returned the negative of the data type OID. This could be confused with valid type OIDs, however.

- Support `long long` types on platforms that already have 64-bit `long` (Michael Meskes)

###### E.156.3.9.2.1. ecpg Cursors

- Add out-of-scope cursor support in ecpg's native mode (Boszormenyi Zoltan)

  This allows `DECLARE` to use variables that are not in scope when `OPEN` is called. This facility already existed in ecpg's Informix-compatibility mode.

- Allow dynamic cursor names in ecpg (Boszormenyi Zoltan)

- Allow ecpg to use noise words `FROM` and `IN` in `FETCH` and `MOVE` (Boszormenyi Zoltan)

#### E.156.3.10. Build Options

- Enable client thread safety by default (Bruce Momjian)

  The thread-safety option can be disabled with `configure` `--disable-thread-safety`.

- Add support for controlling the Linux out-of-memory killer (Alex Hunsaker, Tom Lane)

  Now that `/proc/self/oom_adj` allows disabling of the Linux out-of-memory (OOM) killer, it's recommendable to disable OOM kills for the postmaster. It may then be desirable to re-enable OOM kills for the postmaster's child processes. The new compile-time option `LINUX_OOM_ADJ` allows the killer to be reactivated for child processes.

##### E.156.3.10.1. Makefiles

- New `Makefile` targets `world`, `install-world`, and `installcheck-world` (Andrew Dunstan)

  These are similar to the existing `all`, `install`, and `installcheck` targets, but they also build the HTML documentation, build and test `contrib`, and test server-side languages and ecpg.

- Add data and documentation installation location control to PGXS Makefiles (Mark Cave-Ayland)

- Add Makefile rules to build the PostgreSQL documentation as a single HTML file or as a single plain-text file (Peter Eisentraut, Bruce Momjian)

##### E.156.3.10.2. Windows

- Support compiling on 64-bit Windows and running in 64-bit mode (Tsutomu Yamada, Magnus Hagander)

  This allows for large shared memory sizes on Windows.

- Support server builds using Visual Studio 2008 (Magnus Hagander)

#### E.156.3.11. Source Code

- Distribute prebuilt documentation in a subdirectory tree, rather than as tar archive files inside the distribution tarball (Peter Eisentraut)

  For example, the prebuilt HTML documentation is now in `doc/src/sgml/html/`; the manual pages are packaged similarly.

- Make the server's lexer reentrant (Tom Lane)

  This was needed for use of the lexer by PL/pgSQL.

- Improve speed of memory allocation (Tom Lane, Greg Stark)

- User-defined constraint triggers now have entries in `pg_constraint` as well as `pg_trigger` (Tom Lane)

  Because of this change, `pg_constraint`.`pgconstrname` is now redundant and has been removed.

- Add system catalog columns `pg_constraint`.`conindid` and `pg_trigger`.`tgconstrindid` to better document the use of indexes for constraint enforcement (Tom Lane)

- Allow multiple conditions to be communicated to backends using a single operating system signal (Fujii Masao)

  This allows new features to be added without a platform-specific constraint on the number of signal conditions.

- Improve source code test coverage, including `contrib`, PL/Python, and PL/Perl (Peter Eisentraut, Andrew Dunstan)

- Remove the use of flat files for system table bootstrapping (Tom Lane, Alvaro Herrera)

  This improves performance when using many roles or databases, and eliminates some possible failure conditions.

- Automatically generate the initial contents of `pg_attribute` for “bootstrapped” catalogs (John Naylor)

  This greatly simplifies changes to these catalogs.

- Split the processing of `INSERT`/`UPDATE`/`DELETE` operations out of `execMain.c` (Marko Tiikkaja)

  Updates are now executed in a separate ModifyTable node. This change is necessary infrastructure for future improvements.

- Simplify translation of psql's SQL help text (Peter Eisentraut)

- Reduce the lengths of some file names so that all file paths in the distribution tarball are less than 100 characters (Tom Lane)

  Some decompression programs have problems with longer file paths.

- Add a new `ERRCODE_INVALID_PASSWORD` `SQLSTATE` error code (Bruce Momjian)

- With authors' permissions, remove the few remaining personal source code copyright notices (Bruce Momjian)

  The personal copyright notices were insignificant but the community occasionally had to answer questions about them.

- Add new documentation section about running PostgreSQL in non-durable mode to improve performance (Bruce Momjian)

- Restructure the HTML documentation `Makefile` rules to make their dependency checks work correctly, avoiding unnecessary rebuilds (Peter Eisentraut)

- Use DocBook XSL stylesheets for man page building, rather than Docbook2X (Peter Eisentraut)

  This changes the set of tools needed to build the man pages.

- Improve PL/Perl code structure (Tim Bunce)

- Improve error context reports in PL/Perl (Alexey Klyukin)

##### E.156.3.11.1. New Build Requirements

Note that these requirements do not apply when building from a distribution tarball, since tarballs include the files that these programs are used to build.

- Require Autoconf 2.63 to build configure (Peter Eisentraut)

- Require Flex 2.5.31 or later to build from a CVS checkout (Tom Lane)

- Require Perl version 5.8 or later to build from a CVS checkout (John Naylor, Andrew Dunstan)

##### E.156.3.11.2. Portability

- Use a more modern API for Bonjour (Tom Lane)

  Bonjour support now requires macOS 10.3 or later. The older API has been deprecated by Apple.

- Add spinlock support for the SuperH architecture (Nobuhiro Iwamatsu)

- Allow non-GCC compilers to use inline functions if they support them (Kurt Harriman)

- Remove support for platforms that don't have a working 64-bit integer data type (Tom Lane)

- Restructure use of `LDFLAGS` to be more consistent across platforms (Tom Lane)

  `LDFLAGS` is now used for linking both executables and shared libraries, and we add on `LDFLAGS_EX` when linking executables, or `LDFLAGS_SL` when linking shared libraries.

##### E.156.3.11.3. Server Programming

- Make backend header files safe to include in C++ (Kurt Harriman, Peter Eisentraut)

  These changes remove keyword conflicts that previously made C++ usage difficult in backend code. However, there are still other complexities when using C++ for backend functions. `extern "C" { }` is still necessary in appropriate places, and memory management and error handling are still problematic.

- Add `AggCheckCallContext()` for use in detecting if a C function is being called as an aggregate (Hitoshi Harada)

- Change calling convention for `SearchSysCache()` and related functions to avoid hard-wiring the maximum number of cache keys (Robert Haas)

  Existing calls will still work for the moment, but can be expected to break in 9.1 or later if not converted to the new style.

- Require calls of `fastgetattr()` and `heap_getattr()` backend macros to provide a non-NULL fourth argument (Robert Haas)

- Custom typanalyze functions should no longer rely on `VacAttrStats`.`attr` to determine the type of data they will be passed (Tom Lane)

  This was changed to allow collection of statistics on index columns for which the storage type is different from the underlying column data type. There are new fields that tell the actual datatype being analyzed.

##### E.156.3.11.4. Server Hooks

- Add parser hooks for processing ColumnRef and ParamRef nodes (Tom Lane)

- Add a ProcessUtility hook so loadable modules can control utility commands (Itagaki Takahiro)

##### E.156.3.11.5. Binary Upgrade Support

- Add `contrib/pg_upgrade` to support in-place upgrades (Bruce Momjian)

  This avoids the requirement of dumping/reloading the database when upgrading to a new major release of PostgreSQL, thus reducing downtime by orders of magnitude. It supports upgrades to 9.0 from PostgreSQL 8.3 and 8.4.

- Add support for preserving relation `relfilenode` values during binary upgrades (Bruce Momjian)

- Add support for preserving `pg_type` and `pg_enum` OIDs during binary upgrades (Bruce Momjian)

- Move data files within tablespaces into PostgreSQL-version-specific subdirectories (Bruce Momjian)

  This simplifies binary upgrades.

#### E.156.3.12. Contrib

- Add multithreading option (`-j`) to `contrib/pgbench` (Itagaki Takahiro)

  This allows multiple CPUs to be used by pgbench, reducing the risk of pgbench itself becoming the test bottleneck.

- Add `\shell` and `\setshell` meta commands to `contrib/pgbench` (Michael Paquier)

- New features for `contrib/dict_xsyn` (Sergey Karpov)

  The new options are `matchorig`, `matchsynonyms`, and `keepsynonyms`.

- Add full text dictionary `contrib/unaccent` (Teodor Sigaev)

  This filtering dictionary removes accents from letters, which makes full-text searches over multiple languages much easier.

- Add `dblink_get_notify()` to `contrib/dblink` (Marcus Kempe)

  This allows asynchronous notifications in dblink.

- Improve `contrib/dblink`'s handling of dropped columns (Tom Lane)

  This affects `dblink_build_sql_insert()` and related functions. These functions now number columns according to logical not physical column numbers.

- Greatly increase `contrib/hstore`'s data length limit, and add B-tree and hash support so `GROUP BY` and `DISTINCT` operations are possible on `hstore` columns (Andrew Gierth)

  New functions and operators were also added. These improvements make `hstore` a full-function key-value store embedded in PostgreSQL.

- Add `contrib/passwordcheck` to support site-specific password strength policies (Laurenz Albe)

  The source code of this module should be modified to implement site-specific password policies.

- Add `contrib/pg_archivecleanup` tool (Simon Riggs)

  This is designed to be used in the `archive_cleanup_command` server parameter, to remove no-longer-needed archive files.

- Add query text to `contrib/auto_explain` output (Andrew Dunstan)

- Add buffer access counters to `contrib/pg_stat_statements` (Itagaki Takahiro)

- Update `contrib/start-scripts/linux` to use `/proc/self/oom_adj` to disable the Linux out-of-memory (OOM) killer (Alex Hunsaker, Tom Lane)