postgresql/doc/TODO

TODO list for PostgreSQL
========================
#A dash (-) marks changes that will appear in the upcoming 8.0 release.#

Bracketed items "[]" have more detail.

Current maintainer:	Bruce Momjian (pgman@candle.pha.pa.us)
Last updated:		Fri Sep 10 18:38:47 EDT 2004

The most recent version of this document can be viewed at the PostgreSQL web site, http://www.PostgreSQL.org.

Remove items before beta?

Urgent
======

* Point-in-time data recovery using backup and write-ahead log,
* Create native Win32 port, http://momjian.postgresql.org/main/writings/pgsql/project/win32.html


Administration
==============

* -Incremental backups
* Remove behavior of postmaster -o after making postmaster/postgres
  flags unique
* -Allow configuration files to be specified in a different directory
* Allow limits on per-db/user connections
* Add group object ownership, so groups can rename/drop/grant on objects,
  so we can implement roles
* -Add the concept of dataspaces/tablespaces (Gavin)
* -Allow logging of only data definition(DDL), or DDL and modification statements
* -Allow log lines to include session-level information, like database and user
* Allow server log information to be output as INSERT statements

  This would allow server log information to be easily loaded into
  a database for analysis.

* Prevent default re-use of sysids for dropped users and groups

  Currently, if a user is removed while he still owns objects, a new
  user given might be given their user id and inherit the
  previous users objects.

* Prevent dropping user that still owns objects, or auto-drop the objects
* Allow pooled connections to list all prepared queries

  This would allow an application inheriting a pooled connection to know
  the queries prepared in the current session.

* Allow major upgrades without dump/reload, perhaps using pg_upgrade
* Have SHOW ALL and pg_settings show descriptions for server-side variables
* -Allow external interfaces to extend the GUC variable set
* Allow GRANT/REVOKE permissions to be given to all schema objects with one 
  command
* Remove unreferenced table files created by transactions that were
  in-progress when the server terminated abruptly
* Allow reporting of which objects are in which tablespaces

  This item is difficult because a tablespace can contain objects from
  multiple databases. There is a server-side function that returns the
  databases which use a specific tablespace, so this requires a tool
  that will call that function and connect to each database to find the
  objects in each database for that tablespace.

* Allow database recovery where tablespaces can't be created

  When a pg_dump is restored, all tablespaces will attempt to be created
  in their original locations. If this fails, the user must be able to 
  adjust the restore process.

* Add "include file" functionality in postgresql.conf
* Add session start time and last statement time to pg_stat_activity
* Allow server logs to be remotely read using SQL commands
* Allow server configuration parameters to be remotely modified
* Allow administrators to safely terminate individual sessions

  Right now, SIGTERM will terminate a session, but it is treated as
  though the postmaster has paniced and shared memory might not be
  cleaned up properly.  A new signal is needed for safe termination.

* Un-comment all variables in postgresql.conf

  By not showing commented-out variables, we discourage people from 
  thinking that re-commenting a variable returns it to its default.
  This has to address environment variables that are then overridden
  by config file values.  Another option is to allow commented values
  to return to their default values.

* Allow point-in-time recovery to archive partially filled write-ahead 
  logs

  Currently only full WAL files are archived. This means that the most
  recent transactions aren't available for recovery in case of a disk
  failure.

* Create dump tool for write-ahead logs for use in determining
  transaction id for point-in-time recovery
* Set proper permissions on non-system schemas during db creation

  Currently all schemas are owned by the super-user because they are 
  copied from the template1 database.

* Add a function that returns the 'uptime' of the postmaster
* Improve replication solutions
	o Automatic failover

	The proper solution to this will probably the use of a master/slave
	replication solution like Sloney and a connection pooling tool like
	pgpool.

	o Load balancing

	You can use any of the master/slave replication servers to use a
	standby server for data warehousing. To allow read/write queries to
	multiple servers, you need multi-master replication like pgcluster.

	o Allow replication over unreliable or non-persistent links


Data Types
==========

* Remove Money type, add money formatting for decimal type
* -Change factorial to return a numeric (Gavin)
* Change NUMERIC to enforce the maximum precision, and increase it
* Add function to return compressed length of TOAST data values
* Allow INET subnet tests with non-constants to be indexed
* Add transaction_timestamp(), statement_timestamp(), clock_timestamp() functionality

  Current CURRENT_TIMESTAMP returns the start time of the current
  transaction, and gettimeofday() returns the wallclock time. This will
  make time reporting more consistent and will allow reporting of
  the statement start time.

* Have sequence dependency track use of DEFAULT sequences,
  seqname.nextval (?)
* Disallow changing default expression of a SERIAL column (?)
* Allow infinite dates just like infinite timestamps
* -Allow pg_dump to dump sequences using NO_MAXVALUE and NO_MINVALUE
* -Prevent whole-row references from leaking memory, e.g. SELECT COUNT(tab.*)
* Have initdb set DateStyle based on locale?
* Add pg_get_acldef(), pg_get_typedefault(), and pg_get_attrdef()
* Allow to_char to print localized month names
* Allow functions to have a search path specified at creation time
* -Make LENGTH() of CHAR() not count trailing spaces
* Allow substring/replace() to get/set bit values
* Add GUC variable to allow output of interval values in ISO8601 format
* -Support composite types as table columns
* Fix data types where equality comparison isn't intuitive, e.g. box
* Merge hardwired timezone names with the TZ database; allow either kind
  everywhere a TZ name is currently taken
* Allow customization of the known set of TZ names (generalize the
  present australian_timezones hack)


* ARRAYS
	o Allow nulls in arrays
	o Allow MIN()/MAX() on arrays
	o Delay resolution of array expression type so assignment coercion 
	  can be performed on empty array expressions
	o Modify array literal representation to handle array index lower bound
	  of other than one


* BINARY DATA
	o Improve vacuum of large objects, like /contrib/vacuumlo (?)
	o Add security checking for large objects

	Currently large objects entries do not have owners. Permissions can
	only be set at the pg_largeobject table level.

	o Auto-delete large objects when referencing row is deleted

	o Allow read/write into TOAST values like large objects

	This requires the TOAST column to be stored EXTERNAL.


Multi-Language Support
======================

* Add NCHAR (as distinguished from ordinary varchar),
* Allow locale to be set at database creation

  Currently locale can only be set during initdb.

* Allow encoding on a per-column basis

  Right now only one encoding is allowed per database.

* Optimize locale to have minimal performance impact when not used
* Support multiple simultaneous character sets, per SQL92
* Improve Unicode combined character handling (?)
* Add octet_length_server() and octet_length_client()
* Make octet_length_client() the same as octet_length()?
* -Prevent mismatch of frontend/backend encodings from converting bytea
  data from being interpreted as encoded strings
* -Fix upper()/lower() to work for multibyte encodings


Views / Rules
=============

* Automatically create rules on views so they are updateable, per SQL92 [view]
* Add the functionality for WITH CHECK OPTION clause of CREATE VIEW
* Allow NOTIFY in rules involving conditionals
* Have views on temporary tables exist in the temporary namespace
* Allow temporary views on non-temporary tables
* Allow RULE recompilation


Indexes
=======

* -Order duplicate index entries on creation by ctid for faster heap lookups
* Allow inherited tables to inherit index, UNIQUE constraint, and primary
  key, foreign key  [inheritance]
* UNIQUE INDEX on base column not honored on inserts/updates from
  inherited table:  INSERT INTO inherit_table (unique_index_col) VALUES
  (dup) should fail [inheritance]

  The main difficulty with this item is the problem of creating an index
  that can spam more than one table.

* Add UNIQUE capability to non-btree indexes
* Add rtree index support for line, lseg, path, point
* Use indexes for MIN() and MAX()

  MIN/MAX queries can already be rewritten as SELECT col FROM tab ORDER
  BY col {DESC} LIMIT 1. Completing this item involves making this
  transformation automatically.

* Use index to restrict rows returned by multi-key index when used with
  non-consecutive keys to reduce heap accesses

  For an index on col1,col2,col3, and a WHERE clause of col1 = 5 and
  col3 = 9, spin though the index checking for col1 and col3 matches,
  rather than just col1

* -Be smarter about insertion of already-ordered data into btree index
* Prevent index uniqueness checks when UPDATE does not modify the column

  Uniqueness (index) checks are done when updating a column even if the
  column is not modified by the UPDATE.

* Fetch heap pages matching index entries in sequential order [performance]

  Rather than randomly accessing heap pages based on index entries, mark
  heap pages needing access in a bitmap and do the lookups in sequential
  order. Another method would be to sort heap ctids matching the index
  before accessing the heap rows.

* Use bitmaps to combine existing indexes [performance]

  Bitmap indexes allow single indexed columns to be combined to
  dynamically create a composite index to match a specific query. Each
  index is a bitmap, and the bitmaps are AND'ed or OR'ed to be combined.

* Allow use of indexes to search for NULLs

  One solution is to create a partial index on an IS NULL expression.

* -Allow SELECT * FROM tab WHERE int2col = 4 to use int2col index, int8,
  float4, numeric/decimal too
* Add concurrency to GIST
* Pack hash index buckets onto disk pages more efficiently

  Currently no only one hash bucket can be stored on a page. Ideally
  several hash buckets could be stored on a single page and greater
  granularity used for the hash algorithm.


Commands
========

* Add BETWEEN ASYMMETRIC/SYMMETRIC
* Change LIMIT/OFFSET to use int8
* CREATE TABLE AS can not determine column lengths from expressions [atttypmod]
* Allow UPDATE to handle complex aggregates [update] (?)
* -Allow command blocks to ignore certain types of errors
* Allow backslash handling in quoted strings to be disabled for portability

  The use of C-style backslashes (.e.g. \n, \r) in quoted strings is not
  SQL-spec compliant, so allow such handling to be disabled.

* Allow an alias to be provided for the target table in UPDATE/DELETE

  This is not SQL-spec but many DBMSs allow it.

* Allow additional tables to be specified in DELETE for joins

  UPDATE already allows this (UPDATE...FROM) but we need similar
  functionality in DELETE.  It's been agreed that the keyword should 
  be USING, to avoid anything as confusing as DELETE FROM a FROM b.

* Add CORRESPONDING BY to UNION/INTERSECT/EXCEPT
* Allow REINDEX to rebuild all database indexes, remove /contrib/reindex
* Add ROLLUP, CUBE, GROUPING SETS options to GROUP BY
* Add a schema option to createlang
* -Allow savepoints / nested transactions (Alvaro)
* -Use nested transactions to prevent syntax errors from aborting a transaction
* Allow UPDATE tab SET ROW (col, ...) = (...) for updating multiple columns
* Allow SET CONSTRAINTS to be qualified by schema/table name
* -Prevent COMMENT ON DATABASE from using a database name
* -Add NO WAIT LOCKs
* Allow TRUNCATE ... CASCADE/RESTRICT
* Allow PREPARE of cursors
* Allow PREPARE to automatically determine parameter types based on the SQL 
  statement
* Allow finer control over the caching of prepared query plans

  Currently, queries prepared via the libpq API are planned on first
  execute using the supplied parameters --- allow SQL PREPARE to do the
  same.  Also, allow control over replanning prepared queries either
  manually or automatically when statistics for execute parameters
  differ dramatically from those used during planning.

* Allow LISTEN/NOTIFY to store info in memory rather than tables?

  Currently LISTEN/NOTIFY information is stored in pg_listener. Storing
  such information in memory would improve performance.

* -COMMENT ON [ CAST | CONVERSION | OPERATOR CLASS | LARGE OBJECT | LANGUAGE ] 
  (Christopher) 
* Dump large object comments in custom dump format
* Add optional textual message to NOTIFY

  This would allow an informational message to be added to the notify
  message, perhaps indicating the row modified or other custom
  information.

* -Allow more ISOLATION LEVELS to be accepted
* Allow CREATE TABLE foo (f1 INT CHECK (f1 > 0) CHECK (f1 < 10)) to work
  by searching for non-conflicting constraint names, and prefix with
  table name?
* Use more reliable method for CREATE DATABASE to get a consistent copy
  of db?

  Currently the system uses the operating system COPY command to create
  new database.

* Add C code to copy directories for use in creating new databases
* Ignore temporary tables from other sessions when processing
  inheritance?
* -Add GUC setting to make created tables default to WITHOUT OIDS
* Have pg_ctl look at PGHOST in case it is a socket directory?
* Allow column-level GRANT/REVOKE privileges
* Add a session mode to warn about non-standard SQL usage in queries
* Add MERGE command that does UPDATE/DELETE, or on failure, INSERT (rules, triggers?)
* Add ON COMMIT capability to CREATE TABLE AS SELECT
* Add NOVICE output level for helpful messages like automatic sequence/index creation
* Add COMMENT ON for all cluster global objects (users, groups,
  databases and tablespaces)
* Add an option to automatically use savepoints for each statement in a
  multi-statement transaction.

  When enabled, this would allow errors in multi-statement transactions 
  to be automatically ignored.
* Make row-wise comparisons work per SQL spec


* ALTER
	o -ALTER TABLE ADD COLUMN does not honor DEFAULT and non-CHECK CONSTRAINT
	o -ALTER TABLE ADD COLUMN column DEFAULT should fill existing
	  rows with DEFAULT value
	o -ALTER TABLE ADD COLUMN column SERIAL doesn't create sequence because
          of the item above
	o Have ALTER TABLE RENAME rename SERIAL sequence names
	o -Allow ALTER TABLE to modify column lengths and change to binary
	  compatible types
	o -Add ALTER DATABASE ... OWNER TO newowner
	o Add ALTER DOMAIN TYPE
	o Allow ALTER TABLE ... ALTER CONSTRAINT ... RENAME
	o Allow ALTER TABLE to change constraint deferrability and actions
	o Disallow dropping of an inherited constraint
	o Allow objects to be moved to different schemas
	o Allow ALTER TABLESPACE to move to different directories
	o Allow databases and schemas to be moved to different tablespaces

	One complexity is whether moving a schema should move all existing
	schema objects or just define the location for future object creation.

	o Allow moving system tables to other tablespaces, where possible

	Currently non-global system tables must be in the default database
	schema. Global system tables can never be moved.

	o -Add ALTER DOMAIN, AGGREGATE, CONVERSION ... OWNER TO
	o -Add ALTER SEQUENCE ... OWNER TO
	o -Add ALTER INDEX that works just like ALTER TABLE already does
	  on an index

* CLUSTER
	o Automatically maintain clustering on a table

	This might require some background daemon to maintain clustering
	during periods of low usage. It might also require tables to be only
	paritally filled for easier reorganization.  Another idea would
        be to create a merged heap/index data file so an index lookup would
	automatically access the heap data too.

	o -Add ALTER TABLE table SET WITHOUT CLUSTER (Christopher)
	o Add default clustering to system tables

	To do this, determine the ideal cluster index for each system
	table and set the cluster setting during initdb.

* COPY
	o -Allow dump/load of CSV format
	o Allow COPY to report error lines and continue
	
	This requires the use of a savepoint before each COPY line is
	processed, with ROLLBACK on COPY failure.

	o Allow COPY to understand \x as a hex byte
	o Have COPY return the number of rows loaded/unloaded (?)
	o Allow COPY to optionally include column headings as the first line

* CURSOR
	o Allow UPDATE/DELETE WHERE CURRENT OF cursor
	
	This requires using the row ctid to map cursor rows back to the
	original heap row. This become more complicated if WITH HOLD cursors
	are to be supported because WITH HOLD cursors have a copy of the row
	and no FOR UPDATE lock.

	o Prevent DROP TABLE from dropping a row referenced by its own open
	  cursor (?)

	o Allow pooled connections to list all open WITH HOLD cursors

	Because WITH HOLD cursors exist outside transactions, this allows
	them to be listed so they can be closed.

* INSERT
	o Allow INSERT/UPDATE of the system-generated oid value for a row
	o Allow INSERT INTO tab (col1, ..) VALUES (val1, ..), (val2, ..)
	o Allow INSERT/UPDATE ... RETURNING new.col or old.col
	
	This is useful for returning the auto-generated key for an INSERT.
	One complication is how to handle rules that run as part of
	the insert.

* SHOW/SET
	o Add SET PERFORMANCE_TIPS option to suggest INDEX, VACUUM, VACUUM
	  ANALYZE, and CLUSTER
	o Add SET PATH for schemas (?)

	This is basically the same as SET search_path.
	 
	o Prevent conflicting SET options from being set

	This requires a checking function to be called after the server
	configuration file is read.

* SERVER-SIDE LANGUAGES
	o Allow PL/PgSQL's RAISE function to take expressions (?)

	Currently only constants are supported.

	o Change PL/PgSQL to use palloc() instead of malloc()
	o -Allow Java server-side programming
	o Handle references to temporary tables that are created, destroyed, 
	  then recreated during a session, and EXECUTE is not used
	  
	This requires the cached PL/PgSQL byte code to be invalidated when
	an object referenced in the function is changed.

    o Fix PL/pgSQL RENAME to work on variables other than OLD/NEW
	o Improve PL/PgSQL exception handling using savepoints
	o -Allow PL/pgSQL parameters to be specified by name and type during definition
	o Allow function parameters to be passed by name,
	  get_employee_salary(emp_id => 12345, tax_year => 2001)
	o Add Oracle-style packages
	o Add table function support to pltcl, plperl, plpython (?)
	o Allow PL/pgSQL to name columns by ordinal position, e.g. rec.(3)
	o Allow PL/pgSQL EXECUTE query_var INTO record_var;
	o Add capability to create and call PROCEDURES
	o Allow PL/pgSQL to handle %TYPE arrays, e.g. tab.col%TYPE[]


Clients
=======

* Add XML output to pg_dump and COPY

  We already allow XML to be stored in the database, and XPath queries
  can be used on that data using /contrib/xml2. It also supports XSLT
  transformations.
    
* -Allow psql \du to show users, and add \dg for groups
* -Have psql \dn show only visible temp schemas using current_schemas()
* -Have psql '\i ~/<tab><tab>' actually load files it displays from home dir
* Add a libpq function to support Parse/DescribeStatement capability
* Prevent libpq's PQfnumber() from lowercasing the column name (?)
* Have psql show current values for a sequence
* Move psql backslash database information into the backend, use mnemonic
  commands? [psql]

  This would allow non-psql clients to pull the same information out of
  the database as psql.

* Consistently display privilege information for all objects in psql

* pg_dump
	o Have pg_dump use multi-statement transactions for INSERT dumps
	o -Allow pg_dump to dump CREATE CONVERSION (Christopher)
	o -Make pg_restore continue after errors, so it acts more like pg_dump
	  scripts
	o Allow pg_dump to use multiple -t and -n switches

	  This should be done by allowing a '-t schema.table' syntax.

	o Add dumping of comments on composite type columns
	o Add dumping of comments on index columns
	o Replace crude DELETE FROM method of pg_dumpall for cleaning of
	  users and groups with separate DROP commands
	o Add dumping and restoring of LOB comments
	o Stop dumping CASCADE on DROP TYPE commands in clean mode
	o Add full object name to the tag field.  eg. for operators we need
	  '=(integer, integer)', instead of just '='.
	o Add pg_dumpall custom format dumps. This is probably best done by
	  combining pg_dump and pg_dumpall into a single binary
	o Add CSV output format

* psql tab completion

	o Provide a list of conversions after ALTER CONVERSION?
	o Support for ALTER SEQUENCE clauses
	o Add RENAME TO to ALTER TRIGGER
	o Support for ALTER USER
	o Fix ALTER (GROUP|DOMAIN|...) <sth> DROP
	o Support for ALTER LANGUAGE <sth> RENAME TO
	o Improve support for COPY
	o Improve support for ALTER TABLE

* ECPG (?)
	o Docs

	Document differences between ecpg and the SQL standard and
	information about the Informix-compatibility module.

	o -Implement SET DESCRIPTOR
	o Solve cardinality > 1 for input descriptors / variables (?)
	o Improve error handling (?)
	o Add a semantic check level, e.g. check if a table really exists
	o fix handling of DB attributes that are arrays
	o Use backend PREPARE/EXECUTE facility for ecpg where possible
	o Implement SQLDA
	o Fix nested C comments
	o sqlwarn[6] should be 'W' if the PRECISION or SCALE value specified
	o Make SET CONNECTION thread-aware, non-standard?
	o Allow multidimensional arrays


Referential Integrity
=====================

* Add MATCH PARTIAL referential integrity
* Add deferred trigger queue file

  Right now all deferred trigger information is stored in backend
  memory.  This could exhaust memory for very large trigger queues.
  This item involves dumping large queues into files.

* Implement dirty reads or shared row locks and use them in RI triggers

  Adding shared locks requires recording the table/rows numbers in a 
  shared area, and this could potentially be a large amount of data.
  One idea is to store the table/row numbers in a separate table and set
  a bit on the row indicating looking in this new table is required to
  find any shared row locks.

* Enforce referential integrity for system tables
* Change foreign key constraint for array -> element to mean element
  in array (?)
* Allow DEFERRABLE UNIQUE constraints (?)
* Allow triggers to be disabled [trigger]

  Currently the only way to disable triggers is to modify the system
  tables.

* With disabled triggers, allow pg_dump to use ALTER TABLE ADD FOREIGN KEY

  If the dump is known to be valid, allow foreign keys to be added
  without revalidating the data.

* Allow statement-level triggers to access modified rows
* Support triggers on columns
* -Have AFTER triggers execute after the appropriate SQL statement in a 
  function, not at the end of the function
* -Print table names with constraint names in error messages, or make constraint
  names unique within a schema
* -Issue NOTICE if foreign key data requires costly test to match primary key
* Remove CREATE CONSTRAINT TRIGGER

  This was used in older releases to dump referential integrity
  constraints.

* Allow AFTER triggers on system tables

  System tables are modified in many places in the backend without going
  through the executor and therefore not causing triggers to fire. To
  complete this item, the functions that modify system tables will have
  to fire triggers.


Dependency Checking
===================

* Flush cached query plans when the dependent objects change
* -Use dependency information to dump data in proper order
* -Have pg_dump -c clear the database using dependency information
* Track dependencies in function bodies and recompile/invalidate


Exotic Features
===============

* Add SQL99 WITH clause to SELECT
* Add SQL99 WITH RECURSIVE to SELECT
* Add pre-parsing phase that converts non-ANSI syntax to supported
  syntax

  This could allow SQL written for other databases to run without
  modification.

* Allow plug-in modules to emulate features from other databases
* SQL*Net listener that makes PostgreSQL appear as an Oracle database
  to clients
* Allow queries across databases or servers with transaction
  semantics
	
  Right now contrib/dblink can be used to issue such queries except it
  does not have locking or transaction semantics. Two-phase commit is
  needed to enable transaction semantics.

* Add two-phase commit

  This will involve adding a way to respond to commit failure by either
  taking the server into offline/readonly mode or notifying the
  administrator


PERFORMANCE
===========


Fsync
=====

* Improve commit_delay handling to reduce fsync()
* Determine optimal fdatasync/fsync, O_SYNC/O_DSYNC options
* Allow multiple blocks to be written to WAL with one write()
* Add an option to sync() before fsync()'ing checkpoint files


Cache
=====
* Add free-behind capability for large sequential scans [fadvise]
* Consider use of open/fcntl(O_DIRECT) to minimize OS caching
* Cache last known per-tuple offsets to speed long tuple access

  While column offsets are already cached, the cache can not be used if
  the tuple has NULLs or TOAST columns because these values change the
  typical column offsets. Caching of such offsets could be accomplished
  by remembering the previous offsets and use them again if the row has
  the same pattern.

* Speed up COUNT(*)

  We could use a fixed row count and a +/- count to follow MVCC
  visibility rules, or a single cached value could be used and
  invalidated if anyone modifies the table. [count]


Vacuum
======

* Improve speed with indexes

  For large table adjustements during vacuum, it is faster to reindex
  rather than update the index.

* Reduce lock time by moving tuples with read lock, then write
  lock and truncate table

  Moved tuples are invisible to other backends so they don't require a
  write lock. However, the read lock promotion to write lock could lead
  to deadlock situations.

* -Provide automatic running of vacuum in the background in backend
  rather than in /contrib (Matthew)
* Allow free space map to be auto-sized or warn when it is too small

  The free space map is in shared memory so resizing is difficult.

* Maintain a map of recently-expired rows

  This allows vacuum to reclaim free space without requiring
  a sequential scan


Locking
=======

* Make locking of shared data structures more fine-grained

  This requires that more locks be acquired but this would reduce lock
  contention, improving concurrency.

* Add code to detect an SMP machine and handle spinlocks accordingly
  from distributted.net, http://www1.distributed.net/source, 
  in client/common/cpucheck.cpp

  On SMP machines, it is possible that locks might be released shortly,
  while on non-SMP machines, the backend should sleep so the process
  holding the lock can complete and release it.

* Improve SMP performance on i386 machines

  i386-based SMP machines can generate excessive context switching
  caused by lock failure in high concurrency situations. This may be
  caused by CPU cache line invalidation inefficiencies.

* Research use of sched_yield() for spinlock acquisition failure


Startup Time
============

* Experiment with multi-threaded backend [thread]

  This would prevent the overhead associated with process creation. Most
  operating systems have trivial process creation time compared to
  database startup overhead, but a few operating systems (WIn32,
  Solaris) might benefit from threading.

* Add connection pooling [pool]

  It is unclear if this should be done inside the backend code or done
  by something external like pgpool. The passing of file descriptors to
  existing backends is one of the difficulties with a backend approach.


Write-Ahead Log
===============

* Eliminate need to write full pages to WAL before page modification [wal]

  Currently, to protect against partial disk page writes, we write the
  full page images to WAL before they are modified so we can correct any
  partial page writes during recovery.  These pages can also be
  eliminated from point-in-time archive files.

* Reduce WAL traffic so only modified values are written rather than
  entire rows (?)
* Turn off after-change writes if fsync is disabled

  If fsync is off, there is no purpose in writing full pages to WAL

* Add WAL index reliability improvement to non-btree indexes
* Allow the pg_xlog directory location to be specified during initdb
  with a symlink back to the /data location

* Allow WAL information to recover corrupted pg_controldata
* Find a way to reduce rotational delay when repeatedly writing
  last WAL page
  
  Currently fsync of WAL requires the disk platter to perform a full
  rotation to fsync again. One idea is to write the WAL to different
  offsets that might reduce the rotational delay.

* Allow buffered WAL writes and fsync

  Instead of guaranteeing recovery of all committed transactions, this
  would provide improved performance by delaying WAL writes and fsync
  so an abrupt operating system restart might lose a few seconds of 
  committed transactions but still be consistent.  We could perhaps
  remove the 'fsync' parameter (which results in an an inconsistent
  database) in favor of this capability.


Optimizer / Executor
====================

* Add missing optimizer selectivities for date, r-tree, etc
* Allow ORDER BY ... LIMIT 1 to select high/low value without sort or
  index using a sequential scan for highest/lowest values

  If only one value is needed, there is no need to sort the entire
  table. Instead a sequential scan could get the matching value.

* Precompile SQL functions to avoid overhead
* Add utility to compute accurate random_page_cost value
* Improve ability to display optimizer analysis using OPTIMIZER_DEBUG
* Allow sorting, temp files, temp tables to use multiple work directories

  This allows the I/O load to be spread across multiple disk drives.
* Have EXPLAIN ANALYZE highlight poor optimizer estimates
* Use CHECK constraints to influence optimizer decisions

  CHECK constraints contain information about the distribution of values
  within the table. This is also useful for implementing subtables where
  a tables content is distributed across several subtables.
* Consider using hash buckets to do DISTINCT, rather than sorting

  This would be beneficial when there are few distinct values.


Miscellaneous
=============

* Do async I/O for faster random read-ahead of data

  Async I/O allows multiple I/O requests to be sent to the disk with
  results coming back asynchronously.
    
* Use mmap() rather than SYSV shared memory or to write WAL files (?) [mmap]

  This would remove the requirement for SYSV SHM but would introduce
  portability issues. Anonymous mmap is required to prevent I/O
  overhead.

* Add a script to ask system configuration questions and tune postgresql.conf
* -Use background process to write dirty shared buffers to disk
* Use a phantom command counter for nested subtransactions to reduce
  tuple overhead


Source Code
===========

* Add use of 'const' for variables in source tree
* Rename some /contrib modules from pg* to pg_*
* Move some things from /contrib into main tree
* Remove warnings created by -Wcast-align
* Move platform-specific ps status display info from ps_status.c to ports
* Improve access-permissions check on data directory in Cygwin (Tom)
* Add optional CRC checksum to heap and index pages
* -Change representation of whole-tuple parameters to functions
* Clarify use of 'application' and 'command' tags in SGML docs
* Better document ability to build only certain interfaces (Marc)
* Remove or relicense modules that are not under the BSD license, if possible
* Remove memory/file descriptor freeing before ereport(ERROR)
* Acquire lock on a relation before building a relcache entry for it
* Research interaction of setitimer() and sleep() used by statement_timeout
* -Add checks for fclose() failure (Tom)
* -Change CVS ID to PostgreSQL
* -Exit postmaster if postgresql.conf can not be opened
* Rename /scripts directory because they are all C programs now
* Promote debug_query_string into a server-side function current_query()
* Allow the identifier length to be increased via a configure option
* Allow binaries to be statically linked so they are more easily relocated
* Move some /contrib modules out to their own project sites
* Remove Win32 rename/unlink looping if unnecessary


* Wire Protocol Changes
	o Allow dynamic character set handling
	o Add decoded type, length, precision
	o Use compression?
	o Update clients to use data types, typmod, schema.table.column names of
	  result sets using new query protocol


---------------------------------------------------------------------------


Developers who have claimed items are:
--------------------------------------
* Alvaro is Alvaro Herrera <alvherre@dcc.uchile.cl>
* Andrew is Andrew Dunstan <andrew@dunslane.net>
* Bruce is Bruce Momjian <pgman@candle.pha.pa.us> of Software Research Assoc.
* Christopher is Christopher Kings-Lynne <chriskl@familyhealth.com.au> of
    Family Health Network
* Claudio is Claudio Natoli <claudio.natoli@memetrics.com>
* D'Arcy is D'Arcy J.M. Cain <darcy@druid.net> of The Cain Gang Ltd.
* Fabien is Fabien Coelho <coelho@cri.ensmp.fr>
* Gavin is Gavin Sherry <swm@linuxworld.com.au> of Alcove Systems Engineering
* Greg is Greg Sabino Mullane <greg@turnstep.com>
* Hiroshi is Hiroshi Inoue <Inoue@tpf.co.jp>
* Jan is Jan Wieck <JanWieck@Yahoo.com> of Afilias, Inc.
* Joe is Joe Conway <mail@joeconway.com>
* Karel is Karel Zak <zakkr@zf.jcu.cz>
* Kris is Kris Jurka 
* Magnus is Magnus Hagander <mha@sollentuna.net>
* Marc is Marc Fournier <scrappy@hub.org> of PostgreSQL, Inc.
* Matthew T. O'Connor <matthew@zeut.net>
* Michael is Michael Meskes <meskes@postgresql.org> of Credativ
* Neil is Neil Conway <neilc@samurai.com>
* Oleg is Oleg Bartunov <oleg@sai.msu.su>
* Peter is Peter Eisentraut <peter_e@gmx.net>
* Philip is Philip Warner <pjw@rhyme.com.au> of Albatross Consulting Pty. Ltd.
* Rod is Rod Taylor <pg@rbt.ca>
* Simon is Simon Riggs
* Stephan is Stephan Szabo <sszabo@megazone23.bigpanda.com>
* Tatsuo is Tatsuo Ishii <t-ishii@sra.co.jp> of Software Research Assoc.
* Teodor is 
* Tom is Tom Lane <tgl@sss.pgh.pa.us> of Red Hat