下面是一些最引人注意的改变的简介：
新的多版本并行控制（MVCC）特性在多用户环境里可能有一些不同的表现。阅读并理解下面段落，确保你现有的应用将表现出你所希望的特性。
要保证一行的确实存在或者保护它免于被并行更新，我们必须使用 SELECT FOR UPDATE 或一个合适的 LOCK TABLE 语句。我们在从以前的 Postgres 和其他环境移植应用时必须考虑这一点。
如果你正用 contrib/refint.* 触发器保证参考完整性，你就必须记住上面几条。现在还需要额外的技巧。一个方法是：如果一个事务准备更新/删除一个主键时，使用 LOCK parent_table IN SHARE ROW EXCLUSIVE MODE 命令，如果一个事务准备更新/插入一个外键时使用 LOCK parent_table IN SHARE MODE 命令。
注意：要注意如果你运行一个处于 SERIALIZABLE 模式下的事务，在该事务里，你必须在执行任何 DML（SELECT/INSERT/DELETE/UPDATE/FETCH/COPY_TO） 语句之前执行上面提到的 LOCK 命令。这些不便将在今后我们实现了读污染（未提交）数据的能力（不管什么隔离级别）和真正的参考完整性后消失。
Bug Fixes --------- Fix text<->float8 and text<->float4 conversion functions(Thomas) Fix for creating tables with mixed-case constraints(Billy) Change exp()/pow() behavior to generate error on underflow/overflow(Jan) Fix bug in pg_dump -z Memory overrun cleanups(Tatsuo) Fix for lo_import crash(Tatsuo) Adjust handling of data type names to suppress double quotes(Thomas) Use type coercion for matching columns and DEFAULT(Thomas) Fix deadlock so it only checks once after one second of sleep(Bruce) Fixes for aggregates and PL/pgsql(Hiroshi) Fix for subquery crash(Vadim) Fix for libpq function PQfnumber and case-insensitive names(Bahman Rafatjoo) Fix for large object write-in-middle, no extra block, memory consumption(Tatsuo) Fix for pg_dump -d or -D and quote special characters in INSERT Repair serious problems with dynahash(Tom) Fix INET/CIDR portability problems Fix problem with selectivity error in ALTER TABLE ADD COLUMN(Bruce) Fix executor so mergejoin of different column types works(Tom) Fix for Alpha OR selectivity bug Fix OR index selectivity problem(Bruce) Fix so \d shows proper length for char()/varchar()(Ryan) Fix tutorial code(Clark) Improve destroyuser checking(Oliver) Fix for Kerberos(Rodney McDuff) Fix for dropping database while dirty buffers(Bruce) Fix so sequence nextval() can be case-sensitive(Bruce) Fix !!= operator Drop buffers before destroying database files(Bruce) Fix case where executor evaluates functions twice(Tatsuo) Allow sequence nextval actions to be case-sensitive(Bruce) Fix optimizer indexing not working for negative numbers(Bruce) Fix for memory leak in executor with fjIsNull Fix for aggregate memory leaks(Erik Riedel) Allow username containing a dash GRANT permissions Cleanup of NULL in inet types Clean up system table bugs(Tom) Fix problems of PAGER and \? command(Masaaki Sakaida) Reduce default multi-segment file size limit to 1GB(Peter) Fix for dumping of CREATE OPERATOR(Tom) Fix for backward scanning of cursors(Hiroshi Inoue) Fix for COPY FROM STDIN when using \i(Tom) Fix for subselect is compared inside an expression(Jan) Fix handling of error reporting while returning rows(Tom) Fix problems with reference to array types(Tom,Jan) Prevent UPDATE SET oid(Jan) Fix pg_dump so -t option can handle case-sensitive tablenames Fixes for GROUP BY in special cases(Tom, Jan) Fix for memory leak in failed queries(Tom) DEFAULT now supports mixed-case identifiers(Tom) Fix for multi-segment uses of DROP/RENAME table, indexes(Ole Gjerde) Disable use of pg_dump with both -o and -d options(Bruce) Allow pg_dump to properly dump GROUP permissions(Bruce) Fix GROUP BY in INSERT INTO table SELECT * FROM table2(Jan) Fix for computations in views(Jan) Fix for aggregates on array indexes(Tom) Fix for DEFAULT handles single quotes in value requiring too many quotes Fix security problem with non-super users importing/exporting large objects(Tom) Rollback of transaction that creates table cleaned up properly(Tom) Fix to allow long table and column names to generate proper serial names(Tom) Enhancements ------------ Add "vacuumdb" utility Speed up libpq by allocating memory better(Tom) EXPLAIN all indices used(Tom) Implement CASE, COALESCE, NULLIF expression(Thomas) New pg_dump table output format(Constantin) Add string min()/max() functions(Thomas) Extend new type coercion techniques to aggregates(Thomas) New moddatetime contrib(Terry) Update to pgaccess 0.96(Constantin) Add routines for single-byte "char" type(Thomas) Improved substr() function(Thomas) Improved multi-byte handling(Tatsuo) Multi-version concurrency control/MVCC(Vadim) New Serialized mode(Vadim) Fix for tables over 2gigs(Peter) New SET TRANSACTION ISOLATION LEVEL(Vadim) New LOCK TABLE IN ... MODE(Vadim) Update ODBC driver(Byron) New NUMERIC data type(Jan) New SELECT FOR UPDATE(Vadim) Handle "NaN" and "Infinity" for input values(Jan) Improved date/year handling(Thomas) Improved handling of backend connections(Magnus) New options ELOG_TIMESTAMPS and USE_SYSLOG options for log files(Massimo) New TCL_ARRAYS option(Massimo) New INTERSECT and EXCEPT(Stefan) New pg_index.indisprimary for primary key tracking(D'Arcy) New pg_dump option to allow dropping of tables before creation(Brook) Speedup of row output routines(Tom) New READ COMMITTED isolation level(Vadim) New TEMP tables/indexes(Bruce) Prevent sorting if result is already sorted(Jan) New memory allocation optimization(Jan) Allow psql to do \p\g(Bruce) Allow multiple rule actions(Jan) Added LIMIT/OFFSET functionality(Jan) Improve optimizer when joining a large number of tables(Bruce) New intro to SQL from S. Simkovics' Master's Thesis (Stefan, Thomas) New intro to backend processing from S. Simkovics' Master's Thesis (Stefan) Improved int8 support(Ryan Bradetich, Thomas, Tom) New routines to convert between int8 and text/varchar types(Thomas) New bushy plans, where meta-tables are joined(Bruce) Enable right-hand queries by default(Bruce) Allow reliable maximum number of backends to be set at configure time (--with-maxbackends and postmaster switch (-N backends))(Tom) GEQO default now 10 tables because of optimizer speedups(Tom) Allow NULL=Var for MS-SQL portability(Michael, Bruce) Modify contrib check_primary_key() so either "automatic" or "dependent"(Anand) Allow psql \d on a view show query(Ryan) Speedup for LIKE(Bruce) Ecpg fixes/features, see src/interfaces/ecpg/ChangeLog file(Michael) JDBC fixes/features, see src/interfaces/jdbc/CHANGELOG(Peter) Make % operator have precedence like /(Bruce) Add new postgres -O option to allow system table structure changes(Bruce) Update contrib/pginterface/findoidjoins script(Tom) Major speedup in vacuum of deleted rows with indexes(Vadim) Allow non-SQL functions to run different versions based on arguments(Tom) Add -E option that shows actual queries sent by \dt and friends(Masaaki Sakaida) Add version number in startup banners for psql(Masaaki Sakaida) New contrib/vacuumlo removes large objects not referenced(Peter) New initialization for table sizes so non-vacuumed tables perform better(Tom) Improve error messages when a connection is rejected(Tom) Support for arrays of char() and varchar() fields(Massimo) Overhaul of hash code to increase reliability and performance(Tom) Update to PyGreSQL 2.4(D'Arcy) Changed debug options so -d4 and -d5 produce different node displays(Jan) New pg_options: pretty_plan, pretty_parse, pretty_rewritten(Jan) Better optimization statistics for system table access(Tom) Better handling of non-default block sizes(Massimo) Improve GEQO optimizer memory consumption(Tom) UNION now suppports ORDER BY of columns not in target list(Jan) Major libpq++ improvements(Vince Vielhaber) pg_dump now uses -z(ACL's) as default(Bruce) backend cache, memory speedups(Tom) have pg_dump do everything in one snapshot transaction(Vadim) fix for large object memory leakage, fix for pg_dumping(Tom) INET type now respects netmask for comparisons Make VACUUM ANALYZE only use a readlock(Vadim) Allow VIEWs on UNIONS(Jan) pg_dump now can generate consistent snapshots on active databases(Vadim) Source Tree Changes ------------------- Improve port matching(Tom) Portability fixes for SunOS Add NT/Win32 backend port and enable dynamic loading(Magnus and Daniel Horak) New port to Cobalt Qube(Mips) running Linux(Tatsuo) Port to NetBSD/m68k(Mr. Mutsuki Nakajima) Port to NetBSD/sun3(Mr. Mutsuki Nakajima) Port to NetBSD/macppc(Toshimi Aoki) Fix for tcl/tk configuration(Vince) Removed CURRENT keyword for rule queries(Jan) NT dynamic loading now works(Daniel Horak) Add ARM32 support(Andrew McMurry) Better support for HPUX 11 and Unixware Improve file handling to be more uniform, prevent file descriptor leak(Tom) New install commands for plpgsql(Jan)