Release 8.3

PostgreSQL 9.1.2 Documentation
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# E.39. Release 8.3

> Release Date: 2008-02-04

## E.39.1. Overview

With significant new functionality and performance enhancements, this release represents a major leap forward for PostgreSQL. This was made possible by a growing community that has dramatically accelerated the pace of development. This release adds the following major features:

- Full text search is integrated into the core database system

- Support for the SQL/XML standard, including new operators and an `XML` data type

- Enumerated data types (`ENUM`)

- Arrays of composite types

- Universally Unique Identifier (`UUID`) data type

- Add control over whether `NULL`s sort first or last

- Updatable cursors

- Server configuration parameters can now be set on a per-function basis

- User-defined types can now have type modifiers

- Automatically re-plan cached queries when table definitions change or statistics are updated

- Numerous improvements in logging and statistics collection

- Support Security Service Provider Interface (SSPI) for authentication on Windows

- Support multiple concurrent autovacuum processes, and other autovacuum improvements

- Allow the whole PostgreSQL distribution to be compiled with Microsoft Visual C++

Major performance improvements are listed below. Most of these enhancements are automatic and do not require user changes or tuning:

- Asynchronous commit delays writes to WAL during transaction commit

- Checkpoint writes can be spread over a longer time period to smooth the I/O spike during each checkpoint

- Heap-Only Tuples (HOT) accelerate space reuse for most `UPDATE`s and `DELETE`s

- Just-in-time background writer strategy improves disk write efficiency

- Using non-persistent transaction IDs for read-only transactions reduces overhead and `VACUUM` requirements

- Per-field and per-row storage overhead has been reduced

- Large sequential scans no longer force out frequently used cached pages

- Concurrent large sequential scans can now share disk reads

- `ORDER BY ... LIMIT` can be done without sorting

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

## E.39.2. Migration to Version 8.3

A dump/restore using pg_dump is required for those wishing to migrate data from any previous release.

Observe the following incompatibilities:

### E.39.2.1. General

- Non-character data types are no longer automatically cast to `TEXT` (Peter, Tom)

  Previously, if a non-character value was supplied to an operator or function that requires `text` input, it was automatically cast to `text`, for most (though not all) built-in data types. This no longer happens: an explicit cast to `text` is now required for all non-character-string types. For example, these expressions formerly worked:

      substr(current_date, 1, 4)
      23 LIKE '2%'

  but will now draw "function does not exist" and "operator does not exist" errors respectively. Use an explicit cast instead:

      substr(current_date::text, 1, 4)
      23::text LIKE '2%'

  (Of course, you can use the more verbose `CAST()` syntax too.) The reason for the change is that these automatic casts too often caused surprising behavior. An example is that in previous releases, this expression was accepted but did not do what was expected:

      current_date < 2017-11-17

  This is actually comparing a date to an integer, which should be (and now is) rejected — but in the presence of automatic casts both sides were cast to `text` and a textual comparison was done, because the `text < text` operator was able to match the expression when no other `<` operator could.

  Types `char(`n`)` and `varchar(`n`)` still cast to `text` automatically. Also, automatic casting to `text` still works for inputs to the concatenation (`||`) operator, so long as least one input is a character-string type.

- Full text search features from `contrib/tsearch2` have been moved into the core server, with some minor syntax changes

  `contrib/tsearch2` now contains a compatibility interface.

- `ARRAY(SELECT ...)`, where the `SELECT` returns no rows, now returns an empty array, rather than NULL (Tom)

- The array type name for a base data type is no longer always the base type's name with an underscore prefix

  The old naming convention is still honored when possible, but application code should no longer depend on it. Instead use the new `pg_type.typarray` column to identify the array data type associated with a given type.

- `ORDER BY ... USING` `operator` must now use a less-than or greater-than `operator` that is defined in a btree operator class

  This restriction was added to prevent inconsistent results.

- `SET LOCAL` changes now persist until the end of the outermost transaction, unless rolled back (Tom)

  Previously `SET LOCAL`'s effects were lost after subtransaction commit (`RELEASE SAVEPOINT` or exit from a PL/pgSQL exception block).

- Commands rejected in transaction blocks are now also rejected in multiple-statement query strings (Tom)

  For example, `"BEGIN; DROP DATABASE; COMMIT"` will now be rejected even if submitted as a single query message.

- `ROLLBACK` outside a transaction block now issues `NOTICE` instead of `WARNING` (Bruce)

- Prevent `NOTIFY`/`LISTEN`/`UNLISTEN` from accepting schema-qualified names (Bruce)

  Formerly, these commands accepted `schema.relation` but ignored the schema part, which was confusing.

- `ALTER SEQUENCE` no longer affects the sequence's `currval()` state (Tom)

- Foreign keys now must match indexable conditions for cross-data-type references (Tom)

  This improves semantic consistency and helps avoid performance problems.

- Restrict object size functions to users who have reasonable permissions to view such information (Tom)

  For example, `pg_database_size()` now requires `CONNECT` permission, which is granted to everyone by default. `pg_tablespace_size()` requires `CREATE` permission in the tablespace, or is allowed if the tablespace is the default tablespace for the database.

- Remove the undocumented `!!=` (not in) operator (Tom)

  `NOT IN (SELECT ...)` is the proper way to perform this operation.

- Internal hashing functions are now more uniformly-distributed (Tom)

  If application code was computing and storing hash values using internal PostgreSQL hashing functions, the hash values must be regenerated.

- C-code conventions for handling variable-length data values have changed (Greg Stark, Tom)

  The new `SET_VARSIZE()` macro must be used to set the length of generated `varlena` values. Also, it might be necessary to expand ("de-TOAST") input values in more cases.

- Continuous archiving no longer reports each successful archive operation to the server logs unless `DEBUG` level is used (Simon)

### E.39.2.2. Configuration Parameters

- Numerous changes in administrative server parameters

  `bgwriter_lru_percent`, `bgwriter_all_percent`, `bgwriter_all_maxpages`, `stats_start_collector`, and `stats_reset_on_server_start` are removed. `redirect_stderr` is renamed to `logging_collector`. `stats_command_string` is renamed to `track_activities`. `stats_block_level` and `stats_row_level` are merged into `track_counts`. A new boolean configuration parameter, `archive_mode`, controls archiving. Autovacuum's default settings have changed.

- Remove `stats_start_collector` parameter (Tom)

  We now always start the collector process, unless UDP socket creation fails.

- Remove `stats_reset_on_server_start` parameter (Tom)

  This was removed because `pg_stat_reset()` can be used for this purpose.

- Commenting out a parameter in `postgresql.conf` now causes it to revert to its default value (Joachim Wieland)

  Previously, commenting out an entry left the parameter's value unchanged until the next server restart.

### E.39.2.3. Character Encodings

- Add more checks for invalidly-encoded data (Andrew)

  This change plugs some holes that existed in literal backslash escape string processing and `COPY` escape processing. Now the de-escaped string is rechecked to see if the result created an invalid multi-byte character.

- Disallow database encodings that are inconsistent with the server's locale setting (Tom)

  On most platforms, `C` locale is the only locale that will work with any database encoding. Other locale settings imply a specific encoding and will misbehave if the database encoding is something different. (Typical symptoms include bogus textual sort order and wrong results from `upper()` or `lower()`.) The server now rejects attempts to create databases that have an incompatible encoding.

- Ensure that `chr()` cannot create invalidly-encoded values (Andrew)

  In UTF8-encoded databases the argument of `chr()` is now treated as a Unicode code point. In other multi-byte encodings `chr()`'s argument must designate a 7-bit ASCII character. Zero is no longer accepted. `ascii()` has been adjusted to match.

- Adjust `convert()` behavior to ensure encoding validity (Andrew)

  The two argument form of `convert()` has been removed. The three argument form now takes a `bytea` first argument and returns a `bytea`. To cover the loss of functionality, three new functions have been added:

  - `convert_from(bytea, name)` returns `text` — converts the first argument from the named encoding to the database encoding

  - `convert_to(text, name)` returns `bytea` — converts the first argument from the database encoding to the named encoding

  - `length(bytea, name)` returns `integer` — gives the length of the first argument in characters in the named encoding

- Remove `convert(argument USING conversion_name)` (Andrew)

  Its behavior did not match the SQL standard.

- Make JOHAB encoding client-only (Tatsuo)

  JOHAB is not safe as a server-side encoding.

## E.39.3. Changes

Below you will find a detailed account of the changes between PostgreSQL 8.3 and the previous major release.

### E.39.3.1. Performance

- Asynchronous commit delays writes to WAL during transaction commit (Simon)

  This feature dramatically increases performance for short data-modifying transactions. The disadvantage is that because disk writes are delayed, if the database or operating system crashes before data is written to the disk, committed data will be lost. This feature is useful for applications that can accept some data loss. Unlike turning off `fsync`, using asynchronous commit does not put database consistency at risk; the worst case is that after a crash the last few reportedly-committed transactions might not be committed after all. This feature is enabled by turning off `synchronous_commit` (which can be done per-session or per-transaction, if some transactions are critical and others are not). `wal_writer_delay` can be adjusted to control the maximum delay before transactions actually reach disk.

- Checkpoint writes can be spread over a longer time period to smooth the I/O spike during each checkpoint (Itagaki Takahiro and Heikki Linnakangas)

  Previously all modified buffers were forced to disk as quickly as possible during a checkpoint, causing an I/O spike that decreased server performance. This new approach spreads out disk writes during checkpoints, reducing peak I/O usage. (User-requested and shutdown checkpoints are still written as quickly as possible.)

- Heap-Only Tuples (HOT) accelerate space reuse for most `UPDATE`s and `DELETE`s (Pavan Deolasee, with ideas from many others)

  `UPDATE`s and `DELETE`s leave dead tuples behind, as do failed `INSERT`s. Previously only `VACUUM` could reclaim space taken by dead tuples. With HOT dead tuple space can be automatically reclaimed at the time of `INSERT` or `UPDATE` if no changes are made to indexed columns. This allows for more consistent performance. Also, HOT avoids adding duplicate index entries.

- Just-in-time background writer strategy improves disk write efficiency (Greg Smith, Itagaki Takahiro)

  This greatly reduces the need for manual tuning of the background writer.

- Per-field and per-row storage overhead have been reduced (Greg Stark, Heikki Linnakangas)

  Variable-length data types with data values less than 128 bytes long will see a storage decrease of 3 to 6 bytes. For example, two adjacent `char(1)` fields now use 4 bytes instead of 16. Row headers are also 4 bytes shorter than before.

- Using non-persistent transaction IDs for read-only transactions reduces overhead and `VACUUM` requirements (Florian Pflug)

  Non-persistent transaction IDs do not increment the global transaction counter. Therefore, they reduce the load on `pg_clog` and increase the time between forced vacuums to prevent transaction ID wraparound. Other performance improvements were also made that should improve concurrency.

- Avoid incrementing the command counter after a read-only command (Tom)

  There was formerly a hard limit of 232 (4 billion) commands per transaction. Now only commands that actually changed the database count, so while this limit still exists, it should be significantly less annoying.

- Create a dedicated WAL writer process to off-load work from backends (Simon)

- Skip unnecessary WAL writes for `CLUSTER` and `COPY` (Simon)

  Unless WAL archiving is enabled, the system now avoids WAL writes for `CLUSTER` and just `fsync()`s the table at the end of the command. It also does the same for `COPY` if the table was created in the same transaction.

- Large sequential scans no longer force out frequently used cached pages (Simon, Heikki, Tom)

- Concurrent large sequential scans can now share disk reads (Jeff Davis)

  This is accomplished by starting the new sequential scan in the middle of the table (where another sequential scan is already in-progress) and wrapping around to the beginning to finish. This can affect the order of returned rows in a query that does not specify `ORDER BY`. The `synchronize_seqscans` configuration parameter can be used to disable this if necessary.

- `ORDER BY ... LIMIT` can be done without sorting (Greg Stark)

  This is done by sequentially scanning the table and tracking just the "top N" candidate rows, rather than performing a full sort of the entire table. This is useful when there is no matching index and the `LIMIT` is not large.

- Put a rate limit on messages sent to the statistics collector by backends (Tom)

  This reduces overhead for short transactions, but might sometimes increase the delay before statistics are tallied.

- Improve hash join performance for cases with many NULLs (Tom)

- Speed up operator lookup for cases with non-exact datatype matches (Tom)

### E.39.3.2. Server

- Autovacuum is now enabled by default (Alvaro)

  Several changes were made to eliminate disadvantages of having autovacuum enabled, thereby justifying the change in default. Several other autovacuum parameter defaults were also modified.

- Support multiple concurrent autovacuum processes (Alvaro, Itagaki Takahiro)

  This allows multiple vacuums to run concurrently. This prevents vacuuming of a large table from delaying vacuuming of smaller tables.

- Automatically re-plan cached queries when table definitions change or statistics are updated (Tom)

  Previously PL/pgSQL functions that referenced temporary tables would fail if the temporary table was dropped and recreated between function invocations, unless `EXECUTE` was used. This improvement fixes that problem and many related issues.

- Add a `temp_tablespaces` parameter to control the tablespaces for temporary tables and files (Jaime Casanova, Albert Cervera, Bernd Helmle)

  This parameter defines a list of tablespaces to be used. This enables spreading the I/O load across multiple tablespaces. A random tablespace is chosen each time a temporary object is created. Temporary files are no longer stored in per-database `pgsql_tmp/` directories but in per-tablespace directories.

- Place temporary tables' TOAST tables in special schemas named `pg_toast_temp_`nnn`` (Tom)

  This allows low-level code to recognize these tables as temporary, which enables various optimizations such as not WAL-logging changes and using local rather than shared buffers for access. This also fixes a bug wherein backends unexpectedly held open file references to temporary TOAST tables.

- Fix problem that a constant flow of new connection requests could indefinitely delay the postmaster from completing a shutdown or a crash restart (Tom)

- Guard against a very-low-probability data loss scenario by preventing re-use of a deleted table's relfilenode until after the next checkpoint (Heikki)

- Fix `CREATE CONSTRAINT TRIGGER` to convert old-style foreign key trigger definitions into regular foreign key constraints (Tom)

  This will ease porting of foreign key constraints carried forward from pre-7.3 databases, if they were never converted using `contrib/adddepend`.

- Fix `DEFAULT NULL` to override inherited defaults (Tom)

  `DEFAULT NULL` was formerly considered a noise phrase, but it should (and now does) override non-null defaults that would otherwise be inherited from a parent table or domain.

- Add new encodings EUC_JIS_2004 and SHIFT_JIS_2004 (Tatsuo)

  These new encodings can be converted to and from UTF-8.

- Change server startup log message from "database system is ready" to "database system is ready to accept connections", and adjust its timing

  The message now appears only when the postmaster is really ready to accept connections.

### E.39.3.3. Monitoring

- Add `log_autovacuum_min_duration` parameter to support configurable logging of autovacuum activity (Simon, Alvaro)

- Add `log_lock_waits` parameter to log lock waiting (Simon)

- Add `log_temp_files` parameter to log temporary file usage (Bill Moran)

- Add `log_checkpoints` parameter to improve logging of checkpoints (Greg Smith, Heikki)

- `log_line_prefix` now supports `%s` and `%c` escapes in all processes (Andrew)

  Previously these escapes worked only for user sessions, not for background database processes.

- Add `log_restartpoints` to control logging of point-in-time recovery restart points (Simon)

- Last transaction end time is now logged at end of recovery and at each logged restart point (Simon)

- Autovacuum now reports its activity start time in `pg_stat_activity` (Tom)

- Allow server log output in comma-separated value (CSV) format (Arul Shaji, Greg Smith, Andrew Dunstan)

  CSV-format log files can easily be loaded into a database table for subsequent analysis.

- Use PostgreSQL-supplied timezone support for formatting timestamps displayed in the server log (Tom)

  This avoids Windows-specific problems with localized time zone names that are in the wrong encoding. There is a new `log_timezone` parameter that controls the timezone used in log messages, independently of the client-visible `timezone` parameter.

- New system view `pg_stat_bgwriter` displays statistics about background writer activity (Magnus)

- Add new columns for database-wide tuple statistics to `pg_stat_database` (Magnus)

- Add an `xact_start` (transaction start time) column to `pg_stat_activity` (Neil)

  This makes it easier to identify long-running transactions.

- Add `n_live_tuples` and `n_dead_tuples` columns to `pg_stat_all_tables` and related views (Glen Parker)

- Merge `stats_block_level` and `stats_row_level` parameters into a single parameter `track_counts`, which controls all messages sent to the statistics collector process (Tom)

- Rename `stats_command_string` parameter to `track_activities` (Tom)

- Fix statistical counting of live and dead tuples to recognize that committed and aborted transactions have different effects (Tom)

### E.39.3.4. Authentication

- Support Security Service Provider Interface (SSPI) for authentication on Windows (Magnus)

- Support GSSAPI authentication (Henry Hotz, Magnus)

  This should be preferred to native Kerberos authentication because GSSAPI is an industry standard.

- Support a global SSL configuration file (Victor Wagner)

- Add `ssl_ciphers` parameter to control accepted SSL ciphers (Victor Wagner)

- Add a Kerberos realm parameter, `krb_realm` (Magnus)

### E.39.3.5. Write-Ahead Log (WAL) and Continuous Archiving

- Change the timestamps recorded in transaction WAL records from time_t to TimestampTz representation (Tom)

  This provides sub-second resolution in WAL, which can be useful for point-in-time recovery.

- Reduce WAL disk space needed by warm standby servers (Simon)

  This change allows a warm standby server to pass the name of the earliest still-needed WAL file to the recovery script, allowing automatic removal of no-longer-needed WAL files. This is done using `%r` in the `restore_command` parameter of `recovery.conf`.

- New boolean configuration parameter, `archive_mode`, controls archiving (Simon)

  Previously setting `archive_command` to an empty string turned off archiving. Now `archive_mode` turns archiving on and off, independently of `archive_command`. This is useful for stopping archiving temporarily.

### E.39.3.6. Queries

- Full text search is integrated into the core database system (Teodor, Oleg)

  Text search has been improved, moved into the core code, and is now installed by default. `contrib/tsearch2` now contains a compatibility interface.

- Add control over whether `NULL`s sort first or last (Teodor, Tom)

  The syntax is `ORDER BY ... NULLS FIRST/LAST`.

- Allow per-column ascending/descending (`ASC`/`DESC`) ordering options for indexes (Teodor, Tom)

  Previously a query using `ORDER BY` with mixed `ASC`/`DESC` specifiers could not fully use an index. Now an index can be fully used in such cases if the index was created with matching `ASC`/`DESC` specifications. `NULL` sort order within an index can be controlled, too.

- Allow `col IS NULL` to use an index (Teodor)

- Updatable cursors (Arul Shaji, Tom)

  This eliminates the need to reference a primary key to `UPDATE` or `DELETE` rows returned by a cursor. The syntax is `UPDATE/DELETE WHERE CURRENT OF`.

- Allow `FOR UPDATE` in cursors (Arul Shaji, Tom)

- Create a general mechanism that supports casts to and from the standard string types (`TEXT`, `VARCHAR`, `CHAR`) for every datatype, by invoking the datatype's I/O functions (Tom)

  Previously, such casts were available only for types that had specialized function(s) for the purpose. These new casts are assignment-only in the to-string direction, explicit-only in the other direction, and therefore should create no surprising behavior.

- Allow `UNION` and related constructs to return a domain type, when all inputs are of that domain type (Tom)

  Formerly, the output would be considered to be of the domain's base type.

- Allow limited hashing when using two different data types (Tom)

  This allows hash joins, hash indexes, hashed subplans, and hash aggregation to be used in situations involving cross-data-type comparisons, if the data types have compatible hash functions. Currently, cross-data-type hashing support exists for `smallint`/`integer`/`bigint`, and for `float4`/`float8`.

- Improve optimizer logic for detecting when variables are equal in a `WHERE` clause (Tom)

  This allows mergejoins to work with descending sort orders, and improves recognition of redundant sort columns.

- Improve performance when planning large inheritance trees in cases where most tables are excluded by constraints (Tom)

### E.39.3.7. Object Manipulation

- Arrays of composite types (David Fetter, Andrew, Tom)

  In addition to arrays of explicitly-declared composite types, arrays of the rowtypes of regular tables and views are now supported, except for rowtypes of system catalogs, sequences, and TOAST tables.

- Server configuration parameters can now be set on a per-function basis (Tom)

  For example, functions can now set their own `search_path` to prevent unexpected behavior if a different `search_path` exists at run-time. Security definer functions should set `search_path` to avoid security loopholes.

- `CREATE/ALTER FUNCTION` now supports `COST` and `ROWS` options (Tom)

  `COST` allows specification of the cost of a function call. `ROWS` allows specification of the average number or rows returned by a set-returning function. These values are used by the optimizer in choosing the best plan.

- Implement `CREATE TABLE LIKE ... INCLUDING INDEXES` (Trevor Hardcastle, Nikhil Sontakke, Neil)

- Allow `CREATE INDEX CONCURRENTLY` to ignore transactions in other databases (Simon)

- Add `ALTER VIEW ... RENAME TO` and `ALTER SEQUENCE ... RENAME TO` (David Fetter, Neil)

  Previously this could only be done via `ALTER TABLE ... RENAME TO`.

- Make `CREATE/DROP/RENAME DATABASE` wait briefly for conflicting backends to exit before failing (Tom)

  This increases the likelihood that these commands will succeed.

- Allow triggers and rules to be deactivated in groups using a configuration parameter, for replication purposes (Jan)

  This allows replication systems to disable triggers and rewrite rules as a group without modifying the system catalogs directly. The behavior is controlled by `ALTER TABLE` and a new parameter `session_replication_role`.

- User-defined types can now have type modifiers (Teodor, Tom)

  This allows a user-defined type to take a modifier, like `ssnum(7)`. Previously only built-in data types could have modifiers.

### E.39.3.8. Utility Commands

- Non-superuser database owners now are able to add trusted procedural languages to their databases by default (Jeremy Drake)

  While this is reasonably safe, some administrators might wish to revoke the privilege. It is controlled by `pg_pltemplate`.`tmpldbacreate`.

- Allow a session's current parameter setting to be used as the default for future sessions (Tom)

  This is done with `SET ... FROM CURRENT` in `CREATE/ALTER FUNCTION`, `ALTER DATABASE`, or `ALTER ROLE`.

- Implement new commands `DISCARD ALL`, `DISCARD PLANS`, `DISCARD TEMPORARY`, `CLOSE ALL`, and `DEALLOCATE ALL` (Marko Kreen, Neil)

  These commands simplify resetting a database session to its initial state, and are particularly useful for connection-pooling software.

- Make `CLUSTER` MVCC-safe (Heikki Linnakangas)

  Formerly, `CLUSTER` would discard all tuples that were committed dead, even if there were still transactions that should be able to see them under MVCC visibility rules.

- Add new `CLUSTER` syntax: `CLUSTER `table` USING `index`` (Holger Schurig)

  The old `CLUSTER` syntax is still supported, but the new form is considered more logical.

- Fix `EXPLAIN` so it can show complex plans more accurately (Tom)

  References to subplan outputs are now always shown correctly, instead of using `?column`N`?` for complicated cases.

- Limit the amount of information reported when a user is dropped (Alvaro)

  Previously, dropping (or attempting to drop) a user who owned many objects could result in large `NOTICE` or `ERROR` messages listing all these objects; this caused problems for some client applications. The length of the message is now limited, although a full list is still sent to the server log.

### E.39.3.9. Data Types

- Support for the SQL/XML standard, including new operators and an `XML` data type (Nikolay Samokhvalov, Pavel Stehule, Peter)

- Enumerated data types (`ENUM`) (Tom Dunstan)

  This feature provides convenient support for fields that have a small, fixed set of allowed values. An example of creating an `ENUM` type is `CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy')`.

- Universally Unique Identifier (`UUID`) data type (Gevik Babakhani, Neil)

  This closely matches RFC 4122.

- Widen the `MONEY` data type to 64 bits (D'Arcy Cain)

  This greatly increases the range of supported `MONEY` values.

- Fix `float4`/`float8` to handle `Infinity` and `NAN` (Not A Number) consistently (Bruce)

  The code formerly was not consistent about distinguishing `Infinity` from overflow conditions.

- Allow leading and trailing whitespace during input of `boolean` values (Neil)

- Prevent `COPY` from using digits and lowercase letters as delimiters (Tom)

### E.39.3.10. Functions

- Add new regular expression functions `regexp_matches()`, `regexp_split_to_array()`, and `regexp_split_to_table()` (Jeremy Drake, Neil)

  These functions provide extraction of regular expression subexpressions and allow splitting a string using a POSIX regular expression.

- Add `lo_truncate()` for large object truncation (Kris Jurka)

- Implement `width_bucket()` for the `float8` data type (Neil)

- Add `pg_stat_clear_snapshot()` to discard statistics snapshots collected during the current transaction (Tom)

  The first request for statistics in a transaction takes a statistics snapshot that does not change during the transaction. This function allows the snapshot to be discarded and a new snapshot loaded during the next statistics query. This is particularly useful for PL/pgSQL functions, which are confined to a single transaction.

- Add `isodow` option to `EXTRACT()` and `date_part()` (Bruce)

  This returns the day of the week, with Sunday as seven. (`dow` returns Sunday as zero.)

- Add `ID` (ISO day of week) and `IDDD` (ISO day of year) format codes for `to_char()`, `to_date()`, and `to_timestamp()` (Brendan Jurd)

- Make `to_timestamp()` and `to_date()` assume `TM` (trim) option for potentially variable-width fields (Bruce)

  This matches Oracle's behavior.

- Fix off-by-one conversion error in `to_date()`/`to_timestamp()` `D` (non-ISO day of week) fields (Bruce)

- Make `setseed()` return void, rather than a useless integer value (Neil)

- Add a hash function for `NUMERIC` (Neil)

  This allows hash indexes and hash-based plans to be used with `NUMERIC` columns.

- Improve efficiency of `LIKE`/`ILIKE`, especially for multi-byte character sets like UTF-8 (Andrew, Itagaki Takahiro)

- Make `currtid()` functions require `SELECT` privileges on the target table (Tom)

- Add several `txid_*()` functions to query active transaction IDs (Jan)

  This is useful for various replication solutions.

### E.39.3.11. PL/pgSQL Server-Side Language

- Add scrollable cursor support, including directional control in `FETCH` (Pavel Stehule)

- Allow `IN` as an alternative to `FROM` in PL/pgSQL's `FETCH` statement, for consistency with the backend's `FETCH` command (Pavel Stehule)

- Add `MOVE` to PL/pgSQL (Magnus, Pavel Stehule, Neil)

- Implement `RETURN QUERY` (Pavel Stehule, Neil)

  This adds convenient syntax for PL/pgSQL set-returning functions that want to return the result of a query. `RETURN QUERY` is easier and more efficient than a loop around `RETURN NEXT`.

- Allow function parameter names to be qualified with the function's name (Tom)

  For example, `myfunc.myvar`. This is particularly useful for specifying variables in a query where the variable name might match a column name.

- Make qualification of variables with block labels work properly (Tom)

  Formerly, outer-level block labels could unexpectedly interfere with recognition of inner-level record or row references.

- Tighten requirements for `FOR` loop `STEP` values (Tom)

  Prevent non-positive `STEP` values, and handle loop overflows.

- Improve accuracy when reporting syntax error locations (Tom)

### E.39.3.12. Other Server-Side Languages

- Allow type-name arguments to PL/Perl `spi_prepare()` to be data type aliases in addition to names found in `pg_type` (Andrew)

- Allow type-name arguments to PL/Python `plpy.prepare()` to be data type aliases in addition to names found in `pg_type` (Andrew)

- Allow type-name arguments to PL/Tcl `spi_prepare` to be data type aliases in addition to names found in `pg_type` (Andrew)

- Enable PL/PythonU to compile on Python 2.5 (Marko Kreen)

- Support a true PL/Python boolean type in compatible Python versions (Python 2.3 and later) (Marko Kreen)

- Fix PL/Tcl problems with thread-enabled `libtcl` spawning multiple threads within the backend (Steve Marshall, Paul Bayer, Doug Knight)

  This caused all sorts of unpleasantness.

### E.39.3.13. psql

- List disabled triggers separately in `\d` output (Brendan Jurd)

- In `\d` patterns, always match `$` literally (Tom)

- Show aggregate return types in `\da` output (Greg Sabino Mullane)

- Add the function's volatility status to the output of `\df+` (Neil)

- Add `\prompt` capability (Chad Wagner)

- Allow `\pset`, `\t`, and `\x` to specify `on` or `off`, rather than just toggling (Chad Wagner)

- Add `\sleep` capability (Jan)

- Enable `\timing` output for `\copy` (Andrew)

- Improve `\timing` resolution on Windows (Itagaki Takahiro)

- Flush `\o` output after each backslash command (Tom)

- Correctly detect and report errors while reading a `-f` input file (Peter)

- Remove `-u` option (this option has long been deprecated) (Tom)

### E.39.3.14. pg_dump

- Add `--tablespaces-only` and `--roles-only` options to pg_dumpall (Dave Page)

- Add an output file option to pg_dumpall (Dave Page)

  This is primarily useful on Windows, where output redirection of child pg_dump processes does not work.

- Allow pg_dumpall to accept an initial-connection database name rather than the default `template1` (Dave Page)

- In `-n` and `-t` switches, always match `$` literally (Tom)

- Improve performance when a database has thousands of objects (Tom)

- Remove `-u` option (this option has long been deprecated) (Tom)

### E.39.3.15. Other Client Applications

- In initdb, allow the location of the `pg_xlog` directory to be specified (Euler Taveira de Oliveira)

- Enable server core dump generation in pg_regress on supported operating systems (Andrew)

- Add a `-t` (timeout) parameter to pg_ctl (Bruce)

  This controls how long pg_ctl will wait when waiting for server startup or shutdown. Formerly the timeout was hard-wired as 60 seconds.

- Add a pg_ctl option to control generation of server core dumps (Andrew)

- Allow Control-C to cancel clusterdb, reindexdb, and vacuumdb (Itagaki Takahiro, Magnus)

- Suppress command tag output for createdb, createuser, dropdb, and dropuser (Peter)

  The `--quiet` option is ignored and will be removed in 8.4. Progress messages when acting on all databases now go to stdout instead of stderr because they are not actually errors.

### E.39.3.16. libpq

- Interpret the `dbName` parameter of `PQsetdbLogin()` as a `conninfo` string if it contains an equals sign (Andrew)

  This allows use of `conninfo` strings in client programs that still use `PQsetdbLogin()`.

- Support a global SSL configuration file (Victor Wagner)

- Add environment variable `PGSSLKEY` to control SSL hardware keys (Victor Wagner)

- Add `lo_truncate()` for large object truncation (Kris Jurka)

- Add `PQconnectionNeedsPassword()` that returns true if the server required a password but none was supplied (Joe Conway, Tom)

  If this returns true after a failed connection attempt, a client application should prompt the user for a password. In the past applications have had to check for a specific error message string to decide whether a password is needed; that approach is now deprecated.

- Add `PQconnectionUsedPassword()` that returns true if the supplied password was actually used (Joe Conway, Tom)

  This is useful in some security contexts where it is important to know whether a user-supplied password is actually valid.

### E.39.3.17. ecpg

- Use V3 frontend/backend protocol (Michael)

  This adds support for server-side prepared statements.

- Use native threads, instead of pthreads, on Windows (Magnus)

- Improve thread-safety of ecpglib (Itagaki Takahiro)

- Make the ecpg libraries export only necessary API symbols (Michael)

### E.39.3.18. Windows Port

- Allow the whole PostgreSQL distribution to be compiled with Microsoft Visual C++ (Magnus and others)

  This allows Windows-based developers to use familiar development and debugging tools. Windows executables made with Visual C++ might also have better stability and performance than those made with other tool sets. The client-only Visual C++ build scripts have been removed.

- Drastically reduce postmaster's memory usage when it has many child processes (Magnus)

- Allow regression tests to be started by an administrative user (Magnus)

- Add native shared memory implementation (Magnus)

### E.39.3.19. Server Programming Interface (SPI)

- Add cursor-related functionality in SPI (Pavel Stehule)

  Allow access to the cursor-related planning options, and add `FETCH`/`MOVE` routines.

- Allow execution of cursor commands through `SPI_execute` (Tom)

  The macro `SPI_ERROR_CURSOR` still exists but will never be returned.

- SPI plan pointers are now declared as `SPIPlanPtr` instead of `void *` (Tom)

  This does not break application code, but switching is recommended to help catch simple programming mistakes.

### E.39.3.20. Build Options

- Add configure option `--enable-profiling` to enable code profiling (works only with gcc) (Korry Douglas and Nikhil Sontakke)

- Add configure option `--with-system-tzdata` to use the operating system's time zone database (Peter)

- Fix PGXS so extensions can be built against PostgreSQL installations whose pg_config program does not appear first in the `PATH` (Tom)

- Support `gmake draft` when building the SGML documentation (Bruce)

  Unless `draft` is used, the documentation build will now be repeated if necessary to ensure the index is up-to-date.

### E.39.3.21. Source Code

- Rename macro `DLLIMPORT` to `PGDLLIMPORT` to avoid conflicting with third party includes (like Tcl) that define `DLLIMPORT` (Magnus)

- Create "operator families" to improve planning of queries involving cross-data-type comparisons (Tom)

- Update GIN `extractQuery()` API to allow signalling that nothing can satisfy the query (Teodor)

- Move `NAMEDATALEN` definition from `postgres_ext.h` to `pg_config_manual.h` (Peter)

- Provide `strlcpy()` and `strlcat()` on all platforms, and replace error-prone uses of `strncpy()`, `strncat()`, etc (Peter)

- Create hooks to let an external plugin monitor (or even replace) the planner and create plans for hypothetical situations (Gurjeet Singh, Tom)

- Create a function variable `join_search_hook` to let plugins override the join search order portion of the planner (Julius Stroffek)

- Add `tas()` support for Renesas' M32R processor (Kazuhiro Inaoka)

- `quote_identifier()` and pg_dump no longer quote keywords that are unreserved according to the grammar (Tom)

- Change the on-disk representation of the `NUMERIC` data type so that the `sign_dscale` word comes before the weight (Tom)

- Use SYSV semaphores rather than POSIX on Darwin >= 6.0, i.e., OS X 10.2 and up (Chris Marcellino)

- Add acronym and NFS documentation sections (Bruce)

- "Postgres" is now documented as an accepted alias for "PostgreSQL" (Peter)

- Add documentation about preventing database server spoofing when the server is down (Bruce)

### E.39.3.22. Contrib

- Move `contrib` `README` content into the main PostgreSQL documentation (Albert Cervera i Areny)

- Add `contrib/pageinspect` module for low-level page inspection (Simon, Heikki)

- Add `contrib/pg_standby` module for controlling warm standby operation (Simon)

- Add `contrib/uuid-ossp` module for generating `UUID` values using the OSSP UUID library (Peter)

  Use configure `--with-ossp-uuid` to activate. This takes advantage of the new `UUID` builtin type.

- Add `contrib/dict_int`, `contrib/dict_xsyn`, and `contrib/test_parser` modules to provide sample add-on text search dictionary templates and parsers (Sergey Karpov)

- Allow contrib/pgbench to set the fillfactor (Pavan Deolasee)

- Add timestamps to contrib/pgbench `-l` (Greg Smith)

- Add usage count statistics to `contrib/pgbuffercache` (Greg Smith)

- Add GIN support for `contrib/hstore` (Teodor)

- Add GIN support for `contrib/pg_trgm` (Guillaume Smet, Teodor)

- Update OS/X startup scripts in `contrib/start-scripts` (Mark Cotner, David Fetter)

- Restrict `pgrowlocks()` and `dblink_get_pkey()` to users who have `SELECT` privilege on the target table (Tom)

- Restrict `contrib/pgstattuple` functions to superusers (Tom)

- `contrib/xml2` is deprecated and planned for removal in 8.4 (Peter)

  The new XML support in core PostgreSQL supersedes this module.

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