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[postgresql] / doc / TODO

TODO list for PostgreSQL
========================
Last updated:           Mon Feb 17 13:36:55 EST 2003

Current maintainer:     Bruce Momjian (pgman@candle.pha.pa.us)

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

A dash (-) marks changes that will appear in the upcoming 7.4 release.

Bracketed items "[]" have more detailed.


Urgent
======

* Add replication of distributed databases [replication]
        o automatic failover
        o load balancing
        o master/slave replication
        o multi-master replication
        o partition data across servers
        o sample implementation in contrib/rserv
        o queries across databases or servers (two-phase commit)
        o allow replication over unreliable or non-persistent links
        o http://gborg.postgresql.org/project/pgreplication/projdisplay.php
* Point-in-time data recovery using backup and write-ahead log
* Create native Win32 port [win32]


Reporting
=========

* Allow elog() to return error codes, module name, file name, line
  number, not just messages (Peter E)
* Add error codes (Peter E)
* Make error messages more consistent [error]
* Show location of syntax error in query [yacc]


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

* Incremental backups
* Remove unreferenced table files and temp tables during database vacuum
  or postmaster startup (Bruce)
* Remove behavior of postmaster -o after making postmaster/postgres
  flags unique
* Allow easy display of usernames in a group
* Allow configuration files to be specified in a different directory
* Add start time to pg_stat_activity
* Allow limits on per-db/user connections
* Have standalone backend read postgresql.conf
* Add group object ownership, so groups can rename/drop/grant on objects,
  so we can implement roles
* Add the concept of dataspaces/tablespaces [tablespaces]
* Allow incremental backups


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

* Add IPv6 capability to INET/CIDR types
* Remove Money type, add money formatting for decimal type
* Change factorial to return a numeric
* Change NUMERIC data type to use base 10,000 internally
* Change NUMERIC to enforce the maximum precision, and increase it
* Add function to return compressed length of TOAST data values (Tom)
* Allow INET subnet tests using non-constants
* Add now("transaction|statement|clock") functionality
* -Add GUC variables to control floating number output digits (Pedro Ferreira)
* 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


* CONVERSION
        o Allow better handling of numeric constants, type conversion 
          [typeconv]

* ARRAYS
        o Allow nulls in arrays
        o Allow arrays to be ORDER'ed
        o Support construction of array result values in expressions

* BINARY DATA
        o Improve vacuum of large objects, like /contrib/vacuumlo
        o Add security checking for large objects
        o Make file in/out interface for TOAST columns, similar to large object
          interface (force out-of-line storage and no compression)
        o Auto-delete large objects when referencing row is deleted


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

* Add NCHAR (as distinguished from ordinary varchar),
* Allow LOCALE on a per-column basis, default to ASCII
* Support multiple simultaneous character sets, per SQL92
* Improve Unicode combined character handling
* Optimize locale to have minimal performance impact when not used (Peter E)
* Add octet_length_server() and octet_length_client() (Thomas, Tatsuo)
* 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
* Remove Cyrillic recode support

 
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
* Move psql backslash information into views
* Allow RULE recompilation


Indexes
=======

* Allow CREATE INDEX zman_index ON test (date_trunc( 'day', zman ) datetime_ops)
  fails index can't store constant parameters
* Order duplicate index entries by tid 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 from inherited table
  INSERT INTO inherit_table (unique_index_col) VALUES (dup) should fail
  [inheritance]
* Add UNIQUE capability to non-btree indexes
* Add btree index support for reltime, tinterval, regproc
* Add rtree index support for line, lseg, path, point
* Certain indexes will not shrink, e.g. indexes on ever-increasing
  columns and indexes with many duplicate keys
* Use indexes for min() and max() or convert to SELECT col FROM tab ORDER
  BY col DESC LIMIT 1 if appropriate index exists and WHERE clause acceptible
* Allow LIKE indexing optimization for non-ASCII locales
* Use index to restrict rows returned by multi-key index when used with
  non-consecutive keys or OR clauses, so fewer heap accesses
* Be smarter about insertion of already-ordered data into btree index
* Prevent index uniqueness checks when UPDATE does not modifying column
* Use bitmaps to fetch heap pages in sequential order [performance]
* Use bitmaps to combine existing indexes [performance]
* Improve handling of index scans for NULL
* Allow SELECT * FROM tab WHERE int2col = 4 to use int2col index, int8,
  float4, numeric/decimal too [optimizer]
* Add FILLFACTOR to btree index creation
* Add concurrency to GIST
* Improve concurrency of hash indexes (Neil)
* Require DROP COLUMN CASCADE for a column that is part of a multi-column index


Commands
========

* Add BETWEEN ASYMMETRIC/SYMMETRIC (Christopher)
* Allow LIMIT/OFFSET to use expressions
* 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
* Return proper effected tuple count from complex commands [return]
* Allow DELETE to handle table aliases for self-joins [delete]
* Add CORRESPONDING BY to UNION/INTERSECT/EXCEPT
* Allow REINDEX to rebuild all indexes, remove /contrib/reindex
* -Make a transaction-safe TRUNCATE (Rod)
* Add ROLLUP, CUBE, GROUPING SETS options to GROUP BY
* Add schema option to createlang


* 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 Add ALTER TABLE tab SET WITHOUT OIDS
        * Add ALTER SEQUENCE to modify min/max/increment/cache/cycle values

* CLUSTER
        o Automatically maintain clustering on a table
        o Allow CLUSTER to cluster all tables, remove clusterdb

* COPY
        o Allow dump/load of CSV format
        o Allow COPY to report error lines and continue;  optionally
          allow error codes to be specified; requires savepoints or can
          not be run in a multi-statement transaction
        o Allow copy to understand \x as hex

* CURSOR
        o Allow BINARY option to SELECT, just like DECLARE
        o -MOVE 0 should not move to end of cursor (Bruce)
        o Allow UPDATE/DELETE WHERE CURRENT OF cursor using per-cursor tid
          stored in the backend
        o Prevent DROP of table being referenced by our own open cursor
        o Allow cursors outside transactions [cursor]

* INSERT
        o Allow INSERT/UPDATE of 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; handle
          RULE cases (Philip)

* SHOW/SET
        o Add SET PERFORMANCE_TIPS option to suggest INDEX, VACUUM, VACUUM
          ANALYZE, and CLUSTER
        o Add SET SCHEMA
        o Allow EXPLAIN EXECUTE to see prepared plans
        o Allow SHOW of non-modifiable variables, like pg_controldata
        o Add GUC parameter to control the maximum number of rewrite cycles

* SERVER-SIDE LANGUAGES
        o Allow PL/PgSQL's RAISE function to take expressions
        o Change PL/PgSQL to use palloc() instead of malloc()
        o Add untrusted version of plpython
        o Allow Java server-side programming, http://pljava.sourceforge.net
          [java]
        o Fix problems with complex temporary table creation/destruction
          without using PL/PgSQL EXECUTE, needs cache prevention/invalidation
        o Fix PL/pgSQL RENAME to work on variables other than OLD/NEW
        o Improve PL/PgSQL exception handling
        o Allow 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 PL/PgSQL packages
        o Allow array declarations and other data types in PL/PgSQL DECLARE
        o Add PL/PgSQL PROCEDURES that can return multiple values
        o Add table function support to pltcl, plperl, plpython
        o Make PL/PgSQL %TYPE schema-aware
        o Allow PL/PgSQL to support array element assignment


Clients
=======

* Allow psql to show transaction status if backend protocol changes made
* Add XML interface:  psql, pg_dump, COPY, separate server (?)
* -Add schema, cast, and conversion backslash commands to psql (Christopher)
* Allow pg_dump to dump a specific schema
* Allow psql to do table completion for SELECT * FROM schema_part and
  table completion for SELECT * FROM schema_name.

* JDBC
        o Comprehensive test suite. This may be available already.
        o JDBC-standard BLOB support
        o Error Codes (pending backend implementation)
        o Support both 'make' and 'ant'
        o Fix LargeObject API to handle OIDs as unsigned ints
        o Use cursors implicitly to avoid large results (see setCursorName())
        o Add LISTEN/NOTIFY support to the JDBC driver (Barry)

* ECPG
        o Implement set descriptor, using descriptor
        o Make casts work in variable initializations
        o Implement SQLDA
        o Allow multi-threaded use of SQLCA
        o Solve cardinality > 1 for input descriptors / variables
        o Understand structure definitions outside a declare section
        o sqlwarn[6] should be 'W' if the PRECISION or SCALE value specified
        o Improve error handling
        o Allow :var[:index] or :var[<integer>] as cvariable for an array var
        o Add a semantic check level, e.g. check if a table really exists
        o Fix nested C comments
        o Add SQLSTATE
        o fix handling of DB attributes that are arrays

* Python
        o Allow users to register their own types with _pg
        o Allow SELECT to return a dictionary of dictionaries
        o Allow COPY BINARY FROM


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

* Add MATCH PARTIAL referential integrity [foreign]
* Add deferred trigger queue file (Jan)
* Implement dirty reads and use them in RI triggers
* 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]
* -Support statement-level triggers (Neil)
* Support triggers on columns (Neil)


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

* Flush cached query plans when their underlying catalog data changes
* Use dependency information to dump data in proper order


Transactions
============

* Overhaul bufmgr/lockmgr/transaction manager
* Allow savepoints / nested transactions [transactions] (Bruce)


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

* Add SQL99 WITH clause to SELECT (Tom, Fernando)
* Add SQL99 WITH RECURSIVE to SELECT (Tom, Fernando)
* Allow queries across multiple databases [crossdb]
* Add pre-parsing phase that converts non-ANSI features to supported features
* Allow plug-in modules to emulate features from other databases
* SQL*Net listener that makes PostgreSQL appear as an Oracle database
  to clients
* Two-phase commit to implement distributed transactions


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


Fsync
=====

* Delay fsync() when other backends are about to commit too [fsync]
        o Determine optimal commit_delay value
* Determine optimal fdatasync/fsync, O_SYNC/O_DSYNC options
        o Allow multiple blocks to be written to WAL with one write()


Cache
=====
* Shared catalog cache, reduce lseek()'s by caching table size in shared area
* Add free-behind capability for large sequential scans (Bruce)
* Allow binding query args over FE/BE protocol
* Consider use of open/fcntl(O_DIRECT) to minimize OS caching
* Make blind writes go through the file descriptor cache
* Cache last known per-tuple offsets to speed long tuple access


Vacuum
======

* Improve speed with indexes (perhaps recreate index instead) [vacuum]
* Reduce lock time by moving tuples with read lock, then write
  lock and truncate table [vacuum]
* Provide automatic running of vacuum in the background (Tom) [vacuum]
* Allow free space map to be auto-sized or warn when it is too small


Locking
=======

* Make locking of shared data structures more fine-grained
* Add code to detect an SMP machine and handle spinlocks accordingly
  from distributted.net, http://www1.distributed.net/source, 
  in client/common/cpucheck.cpp
* Research use of sched_yield() for spinlock acquisition failure


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

* Experiment with multi-threaded backend [thread]
* Add connection pooling [pool]
* Allow persistent backends [persistent]
* Create a transaction processor to aid in persistent connections and
  connection pooling
* Do listen() in postmaster and accept() in pre-forked backend
* Have pre-forked backend pre-connect to last requested database or pass
  file descriptor to backend pre-forked for matching database


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

* Have after-change WAL write()'s write only modified data to kernel
* Reduce number of after-change WAL writes; they exist only to gaurd against
  partial page writes [wal]
* Turn off after-change writes if fsync is disabled (?)
* Add WAL index reliability improvement to non-btree indexes
* Find proper defaults for postgresql.conf WAL entries
* Add checkpoint_min_warning postgresql.conf option to warn about checkpoints
  that are too frequent
* Allow xlog directory location to be specified during initdb, perhaps
  using symlinks
* Allow pg_xlog to be moved without symlinks


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

* Improve Subplan list handling
* Allow Subplans to use efficient joins(hash, merge) with upper variable
* -Add hash for evaluating GROUP BY aggregates (Tom)
* Allow merge and hash joins on expressions not just simple variables (Tom)
* Make IN/NOT IN have similar performance to EXISTS/NOT EXISTS [exists]
* Missing optimizer selectivities for date, r-tree, etc. [optimizer]
* Allow ORDER BY ... LIMIT to select top values without sort or index
  using a sequential scan for highest/lowest values (Oleg)
* -Inline simple SQL functions to avoid overhead (Tom)
* Precompile SQL functions to avoid overhead (Neil)
* Add utility to compute accurate random_page_cost value
* Improve ability to display optimizer analysis using OPTIMIZER_DEBUG
* Use CHECK constraints to improve optimizer decisions
* Check GUC geqo_threshold to see if it is still accurate
* Allow sorting, temp files, temp tables to use multiple work directories


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

* Do async I/O for faster random read-ahead of data
* -Get faster regex() code from Henry Spencer <henry@zoo.utoronto.ca>
* Use mmap() rather than SYSV shared memory or to write WAL files (?) [mmap]
* Improve caching of attribute offsets when NULLs exist in the row

* Wire Protocol Changes
        o Show transaction status in psql
        o Allow binding of query parameters, support for prepared queries
        o Add optional textual message to NOTIFY
        o Remove hard-coded limits on user/db/password names
        o Remove unused elements of startup packet (unused, tty, passlength)
        o Fix COPY/fastpath protocol?
        o Allow fastpast to pass values in portable format
        o Replication support?
        o Error codes
        o Dynamic character set handling
        o Special passing of binary values in platform-neutral format (bytea?)
        o ecpg improvements?
        o Add decoded type, length, precision
        o Compression?


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
* Modify regression tests to prevent failures do to minor numeric rounding
* -Add OpenBSD's getpeereid() call for local socket authentication
* Improve access-permissions check on data directory in Cygwin (Tom)
* Add --port flag to regression tests
* Add documentation for perl, including mention of DBI/DBD perl location
* 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 befor elog(ERROR)  (Bruce)
* Acquire lock on a relation before building a relcache entry for it
* Research interaction of setitimer() and sleep() used by statement_timeout

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


Developers who have claimed items are:
--------------------------------------
* Barry is Barry Lind <barry@xythos.com>
* Billy is Billy G. Allie <Bill.Allie@mug.org>
* 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
* D'Arcy is D'Arcy J.M. Cain <darcy@druid.net> of The Cain Gang Ltd.
* Dave is Dave Cramer <dave@fastcrypt.com>
* Edmund is Edmund Mergl <E.Mergl@bawue.de>
* Fernando Nasser <fnasser@redhat.com> of Red Hat
* Gavin Sherry <swm@linuxworld.com.au> of Alcove Systems Engineering
* Hiroshi is Hiroshi Inoue <Inoue@tpf.co.jp>
* Karel is Karel Zak <zakkr@zf.jcu.cz>
* Jan is Jan Wieck <JanWieck@Yahoo.com> of PeerDirect Corp.
* Liam is Liam Stewart <liams@redhat.com> of Red Hat
* Marc is Marc Fournier <scrappy@hub.org> of PostgreSQL, Inc.
* Mark is Mark Hollomon <mhh@mindspring.com>
* 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 M is Peter T Mount <peter@retep.org.uk> of Retep Software
* Peter E is Peter Eisentraut <peter_e@gmx.net>
* Philip is Philip Warner <pjw@rhyme.com.au> of Albatross Consulting Pty. Ltd.
* Rod is Rod Taylor <rbt@zort.ca>
* Ross is Ross J. Reedstrom <reedstrm@wallace.ece.rice.edu>
* Stephan is Stephan Szabo <sszabo@megazone23.bigpanda.com>
* Tatsuo is Tatsuo Ishii <t-ishii@sra.co.jp> of Software Research Assoc.
* Thomas is Thomas Lockhart <lockhart@fourpalms.org> of Jet Propulsion Labratory
* Tom is Tom Lane <tgl@sss.pgh.pa.us> of Red Hat
* Vadim is Vadim B. Mikheev <vadim4o@email.com> of Sector Data