E.25. Release 9.2

Allow queries to retrieve data only from indexes, avoiding heap access (Robert Haas, Ibrar Ahmed, Heikki Linnakangas, Tom Lane)

This feature is often called index-only scans. Heap access can be skipped for heap pages containing only tuples that are visible to all sessions, as reported by the visibility map; so the benefit applies mainly to mostly-static data. The visibility map was made crash-safe as a necessary part of implementing this feature.

Add the SP-GiST (Space-Partitioned GiST) index access method (Teodor Sigaev, Oleg Bartunov, Tom Lane)

SP-GiST is comparable to GiST in flexibility, but supports unbalanced partitioned search structures rather than balanced trees. For suitable problems, SP-GiST can be faster than GiST in both index build time and search time.

Allow group commit to work effectively under heavy load (Peter Geoghegan, Simon Riggs, Heikki Linnakangas)

Previously, batching of commits became ineffective as the write workload increased, because of internal lock contention.

Allow uncontended locks to be managed using a new fast-path lock mechanism (Robert Haas)

Reduce overhead of creating virtual transaction ID locks (Robert Haas)

Reduce the overhead of serializable isolation level locks (Dan Ports)

Improve PowerPC and Itanium spinlock performance (Manabu Ori, Robert Haas, Tom Lane)

Reduce overhead for shared invalidation cache messages (Robert Haas)

Move the frequently accessed members of the PGPROC shared memory array to a separate array (Pavan Deolasee, Heikki Linnakangas, Robert Haas)

Improve COPY performance by adding tuples to the heap in batches (Heikki Linnakangas)

Improve GiST index performance for geometric data types by producing better trees with less memory allocation overhead (Alexander Korotkov)

Improve GiST index build times (Alexander Korotkov, Heikki Linnakangas)

Allow hint bits to be set sooner for temporary and unlogged tables (Robert Haas)

Allow sorting to be performed by inlined, non-SQL-callable comparison functions (Peter Geoghegan, Robert Haas, Tom Lane)

Make the number of CLOG buffers scale based on shared_buffers (Robert Haas, Simon Riggs, Tom Lane)

Improve performance of buffer pool scans that occur when tables or databases are dropped (Jeff Janes, Simon Riggs)

Improve performance of checkpointer's fsync-request queue when many tables are being dropped or truncated (Tom Lane)

Pass the safe number of file descriptors to child processes on Windows (Heikki Linnakangas)

This allows Windows sessions to use more open file descriptors than before.

Create a dedicated background process to perform checkpoints (Simon Riggs)

Formerly the background writer did both dirty-page writing and checkpointing. Separating this into two processes allows each goal to be accomplished more predictably.

Improve asynchronous commit behavior by waking the walwriter sooner (Simon Riggs)

Previously, only wal_writer_delay triggered WAL flushing to disk; now filling a WAL buffer also triggers WAL writes.

Allow the bgwriter, walwriter, checkpointer, statistics collector, log collector, and archiver background processes to sleep more efficiently during periods of inactivity (Peter Geoghegan, Tom Lane)

This series of changes reduces the frequency of process wake-ups when there is nothing to do, dramatically reducing power consumption on idle servers.

Allow the planner to generate custom plans for specific parameter values even when using prepared statements (Tom Lane)

In the past, a prepared statement always had a single "generic" plan that was used for all parameter values, which was frequently much inferior to the plans used for non-prepared statements containing explicit constant values. Now, the planner attempts to generate custom plans for specific parameter values. A generic plan will only be used after custom plans have repeatedly proven to provide no benefit. This change should eliminate the performance penalties formerly seen from use of prepared statements (including non-dynamic statements in PL/pgSQL).

Improve the planner's ability to use nested loops with inner index scans (Tom Lane)

The new "parameterized path" mechanism allows inner index scans to use values from relations that are more than one join level up from the scan. This can greatly improve performance in situations where semantic restrictions (such as outer joins) limit the allowed join orderings.

Improve the planning API for foreign data wrappers (Etsuro Fujita, Shigeru Hanada, Tom Lane)

Wrappers can now provide multiple access "paths" for their tables, allowing more flexibility in join planning.

Recognize self-contradictory restriction clauses for non-table relations (Tom Lane)

This check is only performed when constraint_exclusion is on.

Allow indexed_col op ANY(ARRAY[...]) conditions to be used in plain index scans and index-only scans (Tom Lane)

Formerly such conditions could only be used in bitmap index scans.

Support MIN/MAX index optimizations on boolean columns (Marti Raudsepp)

Account for set-returning functions in SELECT target lists when setting row count estimates (Tom Lane)

Fix planner to handle indexes with duplicated columns more reliably (Tom Lane)

Collect and use element-frequency statistics for arrays (Alexander Korotkov, Tom Lane)

This change improves selectivity estimation for the array <@, &&, and @> operators (array containment and overlaps).

Allow statistics to be collected for foreign tables (Etsuro Fujita)

Improve cost estimates for use of partial indexes (Tom Lane)

Improve the planner's ability to use statistics for columns referenced in subqueries (Tom Lane)

Improve statistical estimates for subqueries using DISTINCT (Tom Lane)

Do not treat role names and samerole specified in pg_hba.conf as automatically including superusers (Andrew Dunstan)

This makes it easier to use reject lines with group roles.

Adjust pg_hba.conf processing to handle token parsing more consistently (Brendan Jurd, Álvaro Herrera)

Disallow empty pg_hba.conf files (Tom Lane)

This was done to more quickly detect misconfiguration.

Make superuser privilege imply replication privilege (Noah Misch)

This avoids the need to explicitly assign such privileges.

Attempt to log the current query string during a backend crash (Marti Raudsepp)

Make logging of autovacuum I/O activity more verbose (Greg Smith, Noah Misch)

This logging is triggered by log_autovacuum_min_duration.

Make WAL replay report failures sooner (Fujii Masao)

There were some cases where failures were only reported once the server went into master mode.

Add pg_xlog_location_diff() to simplify WAL location comparisons (Euler Taveira de Oliveira)

This is useful for computing replication lag.

Support configurable event log application names on Windows (MauMau, Magnus Hagander)

This allows different instances to use the event log with different identifiers, by setting the event_source server parameter, which is similar to how syslog_ident works.

Change "unexpected EOF" messages to DEBUG1 level, except when there is an open transaction (Magnus Hagander)

This change reduces log chatter caused by applications that close database connections ungracefully.

Track temporary file sizes and file counts in the pg_stat_database system view (Tomas Vondra)

Add a deadlock counter to the pg_stat_database system view (Magnus Hagander)

Add a server parameter track_io_timing to track I/O timings (Ants Aasma, Robert Haas)

Report checkpoint timing information in pg_stat_bgwriter (Greg Smith, Peter Geoghegan)

Silently ignore nonexistent schemas specified in search_path (Tom Lane)

This makes it more convenient to use generic path settings, which might include some schemas that don't exist in all databases.

Allow superusers to set deadlock_timeout per-session, not just per-cluster (Noah Misch)

This allows deadlock_timeout to be reduced for transactions that are likely to be involved in a deadlock, thus detecting the failure more quickly. Alternatively, increasing the value can be used to reduce the chances of a session being chosen for cancellation due to a deadlock.

Add a server parameter temp_file_limit to constrain temporary file space usage per session (Mark Kirkwood)

Allow a superuser to SET an extension's superuser-only custom variable before loading the associated extension (Tom Lane)

The system now remembers whether a SET was performed by a superuser, so that proper privilege checking can be done when the extension is loaded.

Add postmaster -C option to query configuration parameters (Bruce Momjian)

This allows pg_ctl to better handle cases where PGDATA or -D points to a configuration-only directory.

Replace an empty locale name with the implied value in CREATE DATABASE (Tom Lane)

This prevents cases where pg_database.datcollate or datctype could be interpreted differently after a server restart.

Allow CHECK constraints to be declared NOT VALID (Álvaro Herrera)

Adding a NOT VALID constraint does not cause the table to be scanned to verify that existing rows meet the constraint. Subsequently, newly added or updated rows are checked. Such constraints are ignored by the planner when considering constraint_exclusion, since it is not certain that all rows meet the constraint.

The new ALTER TABLE VALIDATE command allows NOT VALID constraints to be checked for existing rows, after which they are converted into ordinary constraints.

Allow CHECK constraints to be declared NO INHERIT (Nikhil Sontakke, Alex Hunsaker, Álvaro Herrera)

This makes them enforceable only on the parent table, not on child tables.

Add the ability to rename constraints (Peter Eisentraut)

Reduce need to rebuild tables and indexes for certain ALTER TABLE ... ALTER COLUMN TYPE operations (Noah Misch)

Increasing the length limit for a varchar or varbit column, or removing the limit altogether, no longer requires a table rewrite. Similarly, increasing the allowable precision of a numeric column, or changing a column from constrained numeric to unconstrained numeric, no longer requires a table rewrite. Table rewrites are also avoided in similar cases involving the interval, timestamp, and timestamptz types.

Avoid having ALTER TABLE revalidate foreign key constraints in some cases where it is not necessary (Noah Misch)

Add IF EXISTS options to some ALTER commands (Pavel Stehule)

For example, ALTER FOREIGN TABLE IF EXISTS foo RENAME TO bar.

Add ALTER FOREIGN DATA WRAPPER ... RENAME and ALTER SERVER ... RENAME (Peter Eisentraut)

Add ALTER DOMAIN ... RENAME (Peter Eisentraut)

You could already rename domains using ALTER TYPE.

Throw an error for ALTER DOMAIN ... DROP CONSTRAINT on a nonexistent constraint (Peter Eisentraut)

An IF EXISTS option has been added to provide the previous behavior.

Allow CREATE TABLE (LIKE ...) from foreign tables, views, and composite types (Peter Eisentraut)

For example, this allows a table to be created whose schema matches a view.

Fix CREATE TABLE (LIKE ...) to avoid index name conflicts when copying index comments (Tom Lane)

Fix CREATE TABLE ... AS EXECUTE to handle WITH NO DATA and column name specifications (Tom Lane)

Add a security_barrier option for views (KaiGai Kohei, Robert Haas)

This option prevents optimizations that might allow view-protected data to be exposed to users, for example pushing a clause involving an insecure function into the WHERE clause of the view. Such views can be expected to perform more poorly than ordinary views.

Add a new LEAKPROOF function attribute to mark functions that can safely be pushed down into security_barrier views (KaiGai Kohei)

Add support for privileges on data types (Peter Eisentraut)

This adds support for the SQL-conforming USAGE privilege on types and domains. The intent is to be able to restrict which users can create dependencies on types, since such dependencies limit the owner's ability to alter the type.

Check for INSERT privileges in SELECT INTO / CREATE TABLE AS (KaiGai Kohei)

Because the object is being created by SELECT INTO or CREATE TABLE AS, the creator would ordinarily have insert permissions; but there are corner cases where this is not true, such as when ALTER DEFAULT PRIVILEGES has removed such permissions.

Allow the PL/pgSQL OPEN cursor command to supply parameters by name (Yeb Havinga)

Add a GET STACKED DIAGNOSTICS PL/pgSQL command to retrieve exception info (Pavel Stehule)

Speed up PL/pgSQL array assignment by caching type information (Pavel Stehule)

Improve performance and memory consumption for long chains of ELSIF clauses (Tom Lane)

Output the function signature, not just the name, in PL/pgSQL error messages (Pavel Stehule)

Add PL/Python SPI cursor support (Jan Urbanski)

This allows PL/Python to read partial result sets.

Add result metadata functions to PL/Python (Peter Eisentraut)

Specifically, this adds result object functions .colnames, .coltypes, and .coltypmods.

Remove support for Python 2.2 (Peter Eisentraut)

Allow SQL-language functions to reference parameters by name (Matthew Draper)

To use this, simply name the function arguments and then reference the argument names in the SQL function body.

Add a display mode to auto-expand output based on the display width (Peter Eisentraut)

This adds the auto option to the \x command, which switches to the expanded mode when the normal output would be wider than the screen.

Allow inclusion of a script file that is named relative to the directory of the file from which it was invoked (Gurjeet Singh)

This is done with a new command \ir.

Add support for non-ASCII characters in psql variable names (Tom Lane)

Add support for major-version-specific .psqlrc files (Bruce Momjian)

psql already supported minor-version-specific .psqlrc files.

Provide environment variable overrides for psql history and startup file locations (Andrew Dunstan)

PSQL_HISTORY and PSQLRC now determine these file names if set.

Add a \setenv command to modify the environment variables passed to child processes (Andrew Dunstan)

Name psql's temporary editor files with a .sql extension (Peter Eisentraut)

This allows extension-sensitive editors to select the right mode.

Allow psql to use zero-byte field and record separators (Peter Eisentraut)

Various shell tools use zero-byte (NUL) separators, e.g. find.

Make the \timing option report times for failed queries (Magnus Hagander)

Previously times were reported only for successful queries.

Unify and tighten psql's treatment of \copy and SQL COPY (Noah Misch)

This fix makes failure behavior more predictable and honors \set ON_ERROR_ROLLBACK.

Make \d on a sequence show the table/column name owning it (Magnus Hagander)

Show statistics target for columns in \d+ (Magnus Hagander)

Show role password expiration dates in \du (Fabrízio de Royes Mello)

Display comments for casts, conversions, domains, and languages (Josh Kupershmidt)

These are included in the output of \dC+, \dc+, \dD+, and \dL respectively.

Display comments for SQL/MED objects (Josh Kupershmidt)

These are included in the output of \des+, \det+, and \dew+ for foreign servers, foreign tables, and foreign data wrappers respectively.

Change \dd to display comments only for object types without their own backslash command (Josh Kupershmidt)

In psql tab completion, complete SQL keywords in either upper or lower case according to the new COMP_KEYWORD_CASE setting (Peter Eisentraut)

Add tab completion support for EXECUTE (Andreas Karlsson)

Allow tab completion of role references in GRANT/REVOKE (Peter Eisentraut)

Allow tab completion of file names to supply quotes, when necessary (Noah Misch)

Change tab completion support for TABLE to also include views (Magnus Hagander)

Add an --exclude-table-data option to pg_dump (Andrew Dunstan)

This allows dumping of a table's definition but not its data, on a per-table basis.

Add a --section option to pg_dump and pg_restore (Andrew Dunstan)

Valid values are pre-data, data, and post-data. The option can be given more than once to select two or more sections.

Make pg_dumpall dump all roles first, then all configuration settings on roles (Phil Sorber)

This allows a role's configuration settings to mention other roles without generating an error.

Allow pg_dumpall to avoid errors if the postgres database is missing in the new cluster (Robert Haas)

Dump foreign server user mappings in user name order (Peter Eisentraut)

This helps produce deterministic dump files.

Dump operators in a predictable order (Peter Eisentraut)

Tighten rules for when extension configuration tables are dumped by pg_dump (Tom Lane)

Make pg_dump emit more useful dependency information (Tom Lane)

The dependency links included in archive-format dumps were formerly of very limited use, because they frequently referenced objects that appeared nowhere in the dump. Now they represent actual dependencies (possibly indirect) among the dumped objects.

Improve pg_dump's performance when dumping many database objects (Tom Lane)

Adjust pg_upgrade environment variables (Bruce Momjian)

Rename data, bin, and port environment variables to begin with PG, and support PGPORTOLD/PGPORTNEW, to replace PGPORT.

Overhaul pg_upgrade logging and failure reporting (Bruce Momjian)

Create four append-only log files, and delete them on success. Add -r/--retain option to unconditionally retain these files. Also remove pg_upgrade options -g/-G/-l options as unnecessary, and tighten log file permissions.

Make pg_upgrade create a script to incrementally generate more accurate optimizer statistics (Bruce Momjian)

This reduces the time needed to generate minimal cluster statistics after an upgrade.

Allow pg_upgrade to upgrade an old cluster that does not have a postgres database (Bruce Momjian)

Allow pg_upgrade to handle cases where some old or new databases are missing, as long as they are empty (Bruce Momjian)

Allow pg_upgrade to handle configuration-only directory installations (Bruce Momjian)

In pg_upgrade, add -o/-O options to pass parameters to the servers (Bruce Momjian)

This is useful for configuration-only directory installs.

Change pg_upgrade to use port 50432 by default (Bruce Momjian)

This helps avoid unintended client connections during the upgrade.

Reduce cluster locking in pg_upgrade (Bruce Momjian)

Specifically, only lock the old cluster if link mode is used, and do it right after the schema is restored.

Allow pg_stat_statements to aggregate similar queries via SQL text normalization (Peter Geoghegan, Tom Lane)

Users with applications that use non-parameterized SQL will now be able to monitor query performance without detailed log analysis.

Add dirtied and written block counts and read/write times to pg_stat_statements (Robert Haas, Ants Aasma)

Prevent pg_stat_statements from double-counting PREPARE and EXECUTE commands (Tom Lane)

Support SECURITY LABEL on global objects (KaiGai Kohei, Robert Haas)

Specifically, add security labels to databases, tablespaces, and roles.

Allow sepgsql to honor database labels (KaiGai Kohei)

Perform sepgsql permission checks during the creation of various objects (KaiGai Kohei)

Add sepgsql_setcon() and related functions to control the sepgsql security domain (KaiGai Kohei)

Add a user space access cache to sepgsql to improve performance (KaiGai Kohei)