828 lines
32 KiB
Plaintext
828 lines
32 KiB
Plaintext
==================================================
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Frequently Asked Questions (FAQ) for Postgres95
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==================================================
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last updated: Sun Aug 11 01:35:34 EDT 1996
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current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
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original author: Jolly Chen (jolly@cs.berkeley.edu)
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changes in this version (* = modified, + = new):
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* 1.8) What documentation is available for Postgres95?
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* 3.13) What is the maximum size for a tuple?
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* 3.14) I defined indices but my queries don't seem to make use of them. Why?
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* 3.37) What is the time-warp feature and how does it relate to vacuum?
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+ 3.38) How do I tune the database engine for better performace?
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This file is divided approximately as follows:
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1.*) General questions
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2.*) Installation questions
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3.*) Postgres95 Features questions
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4.*) Questions about extending Postgres95
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5.*) Bugs
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Questions answered:
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1.1) What is Postgres95?
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1.2) What does Postgres95 run on?
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1.3) Where can I get Postgres95?
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1.4) What's the copyright on Postgres95?
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1.5) Support for Postgres95
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1.6) Future releases of Postgres95
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1.7) Is there a commercial version of Postgres95?
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1.9) What version of SQL does Postgres95 use?
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1.10) Does Postgres95 work with databases from earlier versions of postgres?
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1.11) How many people use Postgres95?
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2.1) I get the error "cpp: command not found" when I try to compile
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2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
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2.3) initdb doesn't run
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2.4) when I start up the postmaster, I get
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2.5) The system seems to be confused about commas, decimal points, and
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2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
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2.7) The backend compiled successfully, but compiling libpq resulted
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in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
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2.8) Where can I find the bug fixes for postgres95?
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2.9) I can't apply the patches even though everything looks like it should
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work.
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2.10) When I run postmaster, I get a Bad System Call core dumped message.
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2.11) I get the error message "obj/fmgr.h: No such file or directory"
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2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
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2.13) I get the strange make errors right at the beginning:
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2.14) I have changed a source file, but a recompile does not see the
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3.1) How do I specify a KEY or other constraints on a column?
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3.2) Does Postgres95 support nested subqueries?
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3.3) How do I define a unique indices?
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3.4) I've having a lot of problems with using rules.
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3.5) I can't seem to write into the middle of large objects reliably.
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3.6) Does postgres95 have a graphical user interface? A report
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3.7) How can I write client applications to Postgres95?
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3.8) How do I prevent other hosts from accessing my Postgres95
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3.9) How do I set up a pg_group?
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3.10) What is the exact difference between binary cursors and normal cursors?
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3.11) Why doesn't the != operator work?
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3.12) What is a R-tree index and what is it used for?
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3.13) What is the maximum size for a tuple?
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3.14) I defined indices but my queries don't seem to make use of them. Why?
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3.15) Are there ODBC drivers for Postgres95?
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3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
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3.17) How do I do regular expression searches? case-insensitive
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regexp searching?
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3.18) I can't access the database as the 'root' user.
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3.19) I experienced a server crash during a vacuum. How do I remove the
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lock file?
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3.20) What is the difference between the various character types?
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3.21) In a query, how do I detect if a field is NULL?
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3.22) How do I see how the query optimizer is evaluating my query?
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3.23) How do I create a serial field?
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3.24) How do I create a multi-column index?
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3.25) What are the temp_XXX files in my database directory?
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3.26) Why are my table files not getting any smaller after a delete?
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3.27) Why can't I connect to my database from another machine?
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3.28) I get the error 'default index class unsupported' when creating an
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index. How do I do it?
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3.29) Why does creating an index crash the backend server?
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3.30) How do I specify a decimal constant as a float8, or a string as a text?
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3.31) How do I find out what indexes or operations are defined in the
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database?
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3.32) My database is corrupt. I can't do anything. What should I do?
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3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
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3.34) Why does 'createuser' return 'unexpected last match in input()'?
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3.35) All my servers crash under concurrent table access. Why?
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3.36) What tools are available for hooking postgres to Web pages?
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3.37) What is the time-warp feature and how does it relate to vacuum?
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3.38) How do I tune the database engine for better performace?
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4.1) I wrote a user-defined function and when I run it in psql, it
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dumps core.
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4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0
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4.3) I've written some nifty new types and functions for Postgres95.
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4.4) How do I write a C function to return a tuple?
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5.1) How do I find out about bug fixes?
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5.2) How do I make a bug report?
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----------------------------------------------------------------------
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Section 1: General Questions
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----------------------------------------------------------------------
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1.1) What is Postgres95?
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Postgres95 is an enhancement of the POSTGRES database
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management system, a next-generation DBMS research prototype.
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While Postgres95 retains the powerful data model and rich data
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types of POSTGRES, it replaces the PostQuel query language with an
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extended subset of SQL. Postgres95 is free and the complete
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source is available.
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Postgres95 development is being performed by a team of Internet
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developers who all subscribe to the Postgres95 development mailing
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list. The current coordinator is Marc G. Fournier (scrappy@ki.net).
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(See below on how to join). This team is now responsible for all
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current and future development of Postgres95.
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The authors of Postgres95 1.01 were Andrew Yu and Jolly Chen.
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Many others have contributed to the porting, testing, debugging and
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enhancement of the code. The original Postgres code, from which
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Postgres95 is derived, was the effort of many graduate
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students, undergraduate students, and staff programmers
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working under the direction of Professor Michael Stonebraker
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at the University of California, Berkeley.
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1.2) What does Postgres95 run on?
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The authors have compiled and tested Postgres95 on the following
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platforms(some of these compiles require gcc 2.7.0):
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- DEC Alpha AXP on OSF/1 2.0
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- HP PA-RISC on HP-UX 9.0
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- i386 Solaris
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- SUN SPARC on Solaris 2.4
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- SUN SPARC on SunOS 4.1.3
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- DEC MIPS on Ultrix 4.4
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- Intel x86 on Linux 1.2 and Linux ELF
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- OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
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- IBM on AIX 3.2.5
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- BSD/OS 2.0, 2.01 & 2.1
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- SGI MIPS on IRIX 5.3
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The following ports are bundled with the Postgres95 distribution. The
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authors do not have handy access to these platforms but the
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ports have been tested by the others.
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- Motorola MC68K or Intel x86 on NeXTSTEP 3.2
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- Intel x86 on Intel SVR4
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1.3) Where can I get Postgres95?
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The primary anonymous ftp site for postgres95 is:
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ftp://ftp.ki.net/pub/postgres95
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A mirror site exists at:
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ftp://postgres95.vnet.net/pub/postgres95
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1.4) What's the copyright on Postgres95?
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Postgres95 is subject to the following COPYRIGHT.
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POSTGRES95 Data Base Management System
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Copyright (c) 1994-6 Regents of the University of California
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Permission to use, copy, modify, and distribute this software and its
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documentation for any purpose, without fee, and without a written agreement
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is hereby granted, provided that the above copyright notice and this
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paragraph and the following two paragraphs appear in all copies.
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IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
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DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
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LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
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DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
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AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO
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PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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1.5) Support for Postgres95
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There is no official support for Postgres95 from the original
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maintainers or from University of California, Berkeley. It is
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maintained through volunteer effort only.
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With the generosity of the Jason Wright and others at Vnet,
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the postgres95 mailing list now has a new home --
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postgres95@postgres95.vnet.net. It is available for
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discussion of matters pertaining to Postgres95, including but
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not limited to bug reports and fixes. For info on how to
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subscribe, send a mail with the lines in the body (not the
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subject line):
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help
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info postgres95
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to
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majordomo@postgres95.vnet.net
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There is also a digest list available. To subscribe to this list,
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send email to majordomo@postgres95.vnet.net with a BODY of:
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subscribe postgres95-digest
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Digests are sent out to members of this list whenever the main list has
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received around 30k of messages.
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Archives and digests of the new mailing list at Vnet can be found at:
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ftp://postgres95.vnet.net/pub/postgres95/archives
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ftp://postgres95.vnet.net/pub/postgres95/digests
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There is also a developers mailing list available. To subscribe to
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this list, send email to pg95-dev-request@ki.net with a BODY of:
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subscribe pg95-dev
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Additional information about Postgres95 can be found via the
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postgres95 WWW home page at:
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http://www.ki.net/postgres95
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1.6) Future releases of Postgres95
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The latest release of postgres95 is version 1.02.
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1.7) Is there a commercial version of Postgres95?
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Illustra Information Technology (a wholly owned subsidiary of
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Informix Software, Inc.) sells an object-relational
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DBMS called Illustra that was originally based on postgres.
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Illustra has cosmetic similarities to postgres95 but has more
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features, is more robust, performs better, and offers real
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documentation and support. On the flip side, it costs money.
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For more information, contact sales@illustra.com
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1.8) What documentation is available for Postgres95?
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A user manual, manual pages, and some small test examples
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are included in the distribution. The www page contains
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pointers to an implementation guide and five papers written
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about postgres design concepts and features.
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1.9) What version of SQL does Postgres95 use?
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Postgres95 supports a subset of SQL-92. It has most of the
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important constructs but lacks some of the functionality.
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The most visible differences are:
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- no support for primary keys or column constraints
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- no support for nested subqueries
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- no HAVING clause under a GROUP BY
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On the other hand, you get to create user-defined types,
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functions, inheritance etc. If you're willing to help with
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postgres95 coding, eventually we can also add the missing
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features listed above.
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1.10) Does Postgres95 work with databases from earlier versions of postgres?
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Postgres95 v1.02 is compatible with databases created with v1.01.
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Those upgrading from 1.0 to 1.02 should read the directions in the
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MIGRATION_1.0_TO_1.02 directory.
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1.11) How many people use Postgres95?
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Since we don't have any licensing or registration scheme, it's
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impossible to tell. We do know hundreds copies of postgres95
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v1.* have been downloaded, and that there many hundreds of
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subscribers to the mailing lists.
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----------------------------------------------------------------------
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Section 2: Installation Questions
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----------------------------------------------------------------------
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2.1) I get the error "cpp: command not found" when I try to compile
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the backend.
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Edit the src/backend/utils/Gen_fmgrtab.sh script to include the path
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for the cpp for your particular site.
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2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
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Use a more recent version of flex, version 2.5.2. Version 2.5.3
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has a known bug.
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2.3) initdb doesn't run
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* check to see that you have the proper paths set
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* check that the 'postgres' user owns all the right files
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* ensure that there are files in $PGDATA/files, and that they
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are non-empty. If they aren't, then "gmake install" failed for
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some reason
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2.4) when I start up the postmaster, I get
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"FindBackend: could not find a backend to execute..."
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"postmaster: could not find backend to execute..."
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You probably do not have the right path set up. the 'postgres'
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executable needs to be in your path.
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2.5) The system seems to be confused about commas, decimal points, and
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date formats.
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Check your locale configuration. postgres95 uses the locale
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settings of the user that ran the postmaster process. Set those
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accordingly for your operating environment.
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2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
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You need to manually edit the paths in src/Makefile.global to
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your site configuration.
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2.7) The backend compiled successfully, but compiling libpq resulted
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in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
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You've probably installed postgres95 somewhere other than
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/usr/local/postgres, but didn't edit the src/Makefile.global
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accordingly. See question 2.6.
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2.8) Where can I find the bug fixes for postgres95?
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The patches should be applied in the order listed. The patch files
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can be ftp'ed directly from the directory:
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ftp://ftp.ki.net/pub/postgres95
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2.9) I can't apply the patches even though everything looks like it should
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work.
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If you cut and paste directly off your web browser, tabs and
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whitespaces may not be preserved properly. Use the 'save as file'
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option from your web browser instead.
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2.10) When I run postmaster, I get a Bad System Call core dumped message.
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It could be a variety of problems, but first check to see that you
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have system V extensions installed on your kernel. Postgres95
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requires kernel support for shared memory.
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2.11) I get the error message "obj/fmgr.h: No such file or directory"
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This indicates that you did not generate the file fmgr.h
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properly. Something failed in the running of the
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src/backend/utils/Gen_fmgrtab.sh script. Check to see the
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paths used in that script is appropriate to your system.
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2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
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You either do not have shared memory configured properly in kernel
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or you need to enlarge the shared memory available in the kernel.
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The exact amount you need depends on your architecture and how
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many buffers you configure postmaster to run with. For most
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systems, with default buffer sizes, you need a minimum of ~760K.
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2.13) I get the strange make errors right at the beginning:
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warning: NUL character seen; rest of line ignored
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*** missing separator. Stop.
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or
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Is a directory. Stop.
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Eliminate any whitespaces at the end of the PORTNAME line in
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Makefile.global. Extraneous tabs or spaces will confuse the make
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templates.
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2.14) I have changed a source file, but a recompile does not see the
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change?
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The Makefiles do not have the proper dependencies. You have to
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do a 'make clean' and then another 'make'.
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----------------------------------------------------------------------
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Section 3: Postgres95 Features
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----------------------------------------------------------------------
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3.1) How do I specify a KEY or other constraints on a column?
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Column constraints are not supported in postgres95.
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As a consequence, the system does not check for duplicates.
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3.2) Does Postgres95 support nested subqueries?
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Subqueries are not implemented, but they can be simulated using sql
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functions.
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3.3) How do I define a unique indices?
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Postgres95 does not support unique indices. Defining an index does
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not preclude insertion of duplicate index key values.
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3.4) I've having a lot of problems with using rules.
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Currently, the rule system in postgres95 is mostly broken. It
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works enough to support the view mechanism, but that's about it. Use
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postgres95 rules at your own peril.
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3.5) I can't seem to write into the middle of large objects reliably.
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The Inversion large object system in postgres95 is also
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mostly broken. It works well enough for storing large wads
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of data and reading them back out, but the implementation has
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some underlying problems. Use postgres95 large objects at
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your own peril.
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3.6) Does postgres95 have a graphical user interface? A report
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generator? A embedded query language interface?
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No. No. No. Not in the official distribution at least. Some
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users have reported some success at using 'pgbrowse' and 'onyx' as
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frontends to postgres95. Several contributions are working on
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tk based frontend tools. Ask on the mailing list.
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3.7) How can I write client applications to Postgres95?
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Postgres95 supports a C-callable library interface called libpq
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as well as a Tcl-based library interface called libtcl.
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Others have contributed a perl interface and a WWW gateway
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to postgres95. See the postgres95 home pages for more details.
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3.8) How do I prevent other hosts from accessing my Postgres95
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backend?
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Use host-based authentication by modifying the file
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$PGDATA/pg_hba accordingly.
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3.9) How do I set up a pg_group?
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Currently, there is no easy interface to set up user groups.
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You have to explicitly insert/update the pg_group table. For example:
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jolly=> insert into pg_group (groname, grosysid, grolist)
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jolly=> values ('posthackers', '1234', '{5443, 8261}');
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INSERT 548224
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jolly=> grant insert on foo to group posthackers;
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CHANGE
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jolly=>
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The fields in pg_group are:
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groname: the group name. This a char16 and should
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be purely alphanumeric. Do not include underscores
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or other punctuation.
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grosysid: the group id. This is an int4.
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This should be unique for each group.
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grolist: the list of pg_user id's that belong in the group.
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This is an int4[].
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3.10) What is the exact difference between binary cursors and normal cursors?
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Normal cursors return data back in ASCII format. Since data is stored
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natively in binary format, the system must do a conversion to produce
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the ASCII format. In addition, ASCII formats are often large in size
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than binary format. Once the attributes come back in ASCII, often the
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client application then has to convert it to a binary format to
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manipulate it anyway.
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Binary cursors give you back the data in the native binary
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representation. Thus, binary cursors will tend to be a little faster
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since there's less overhead of conversion.
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However, ASCII is architectural neutral whereas binary representation
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can differ between different machine architecture. Thus, if your client
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machine uses a different representation than you server machine, getting
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back attributes in binary format is probably not what you want. Also,
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if your main purpose is displaying the data in ASCII, then getting it
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back in ASCII will save you some effort on the client side.
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|
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3.11) Why doesn't the != operator work?
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|
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SQL specifies <> as the inequality operator, and that is what
|
|
we have defined for the built-in types. You are free, however, to
|
|
extend postgres95 to include the != operator if you like.
|
|
|
|
3.12) What is a R-tree index and what is it used for?
|
|
|
|
An r-tree index is used for indexing spatial data. A hash index can't
|
|
handle range searches. A B-tree index only handles range searches in a
|
|
single dimension. R-tree's can handle multi-dimensional data. For
|
|
example, if a R-tree index can be built on an attribute of type
|
|
'point', the system can more efficient answer queries like select all
|
|
points within a bounding rectangle.
|
|
|
|
The canonical paper that describes the original R-Tree design is:
|
|
|
|
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching."
|
|
Proc of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
|
|
|
|
You can also find this paper in Stonebraker's "Readings in Database
|
|
Systems"
|
|
|
|
3.13) What is the maximum size for a tuple?
|
|
|
|
Tuples are limited to 8K bytes. Taking into account system attributes
|
|
and other overhead, one should stay well shy of 8,000 bytes to be on
|
|
the safe side. To use attributes larger than 8K, try using the large
|
|
objects interface.
|
|
|
|
Tuples do not cross 8k boundaries so a 5k tuple will require 8k
|
|
of storage.
|
|
|
|
3.14) I defined indices but my queries don't seem to make use of them. Why?
|
|
|
|
Postgres95 does not automatically maintain statistics. One has to
|
|
make an explicit 'vacuum' call to update the statistics. After
|
|
statistics are updated, the optimizer has a better shot at using
|
|
indices. Note that the optimizer is limited and does not use indices
|
|
in some circumstances (such as OR clauses).
|
|
|
|
If the system still does not see the index, it is probably because you
|
|
have created an index on a field with the improper *_ops type. For
|
|
example, you have created a CHAR(4) field, but have specified a
|
|
char_ops index type_class.
|
|
|
|
See the create_index manual page for information on what type classes
|
|
are available. It must match the field type.
|
|
|
|
Postgres does not warn the user when the improper index is created.
|
|
|
|
Indexes not used for ORDER BY operations.
|
|
|
|
3.15) Are there ODBC drivers for Postgres95?
|
|
|
|
PostODBC is available as an ODBC driver for Postgres95.
|
|
|
|
For all people being interested in PostODBC, a freely available ODBC
|
|
driver for Postgres95, there are now two mailing lists devoted to the
|
|
discussion of PostODBC. The mailing lists are:
|
|
|
|
postodbc-users@listserv.direct.net
|
|
and
|
|
postodbc-developers@listserv.direct.net
|
|
|
|
these lists are ordinary majordomo mailing lists. You can subscribe
|
|
by sending a mail to
|
|
|
|
majordomo@listserv.direct.net
|
|
|
|
3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
|
|
|
|
Builtin R-Trees can handle polygons and boxes. In theory, R-trees can
|
|
be extended to handle higher number of dimensions. In practice,
|
|
extending R-trees require a bit of work and we don't currently have
|
|
any documentation on how to do it.
|
|
|
|
3.17) How do I do regular expression searches? case-insensitive
|
|
regexp searching?
|
|
|
|
Postgres95 supports the SQL LIKE syntax as well as more general
|
|
regular expression searching with the ~ operator. The !~ is the
|
|
negated regexp operator. ~* and !~* are the case-insensitive regular
|
|
expression operators.
|
|
|
|
3.18) I can't access the database as the 'root' user.
|
|
|
|
You should not create database users with user id 0(root). They will
|
|
be unable to access the database. This is a security precaution
|
|
because of the ability of any user to dynamically link object modules
|
|
into the database engine.
|
|
|
|
3.19) I experienced a server crash during a vacuum. How do I remove the
|
|
lock file?
|
|
|
|
If the server crashes during a vacuum command, chances are it will
|
|
leave a lock file hanging around. Attempts to re-run the vacuum
|
|
command result in
|
|
WARN:can't create lock file -- another vacuum cleaner running?
|
|
|
|
If you are sure that no vacuum is actually running, you can remove the
|
|
file called "pg_vlock" in your database directory (which is
|
|
$PGDATA/base/<dbName>)
|
|
|
|
3.20) What is the difference between the various character types?
|
|
|
|
Type Internal Name Notes
|
|
--------------------------------------------------
|
|
CHAR char 1 character }
|
|
CHAR2 char2 2 characters }
|
|
CHAR4 char4 4 characters } optimized for a fixed length
|
|
CHAR8 char8 8 characters }
|
|
CHAR16 char16 16 characters }
|
|
CHAR(#) bpchar blank padded to the specified fixed length
|
|
VARCHAR(#) varchar size specifies maximum length, no padding
|
|
TEXT text length limited only by maximum tuple length
|
|
BYTEA bytea variable-length array of bytes
|
|
|
|
Remember, you need to use the internal name when creating indexes
|
|
on these fields or when doing other internal operations.
|
|
|
|
The last four types above are "varlena" types (i.e. the first
|
|
four bytes is the length, followed by the data). CHAR(#) and
|
|
VARCHAR(#) allocate the maximum number of bytes no matter how
|
|
much data is stored in the field. TEXT and BYTEA are the only
|
|
character types that have variable length on the disk.
|
|
|
|
3.21) In a query, how do I detect if a field is NULL?
|
|
|
|
Postgres95 has two builtin keywords, "isnull" and "notnull" (note no
|
|
spaces). For example:
|
|
select * from tbl where field isnull
|
|
will return rows from tbl where the field is null valued.
|
|
|
|
3.22) How do I see how the query optimizer is evaluating my query?
|
|
|
|
Place the word 'EXPLAIN' at the beginning of the query, for example:
|
|
|
|
EXPLAIN SELECT * FROM table1 WHERE age = 23;
|
|
|
|
3.23) How do I create a serial field?
|
|
|
|
There is no way to create a serial or unique field in Postgres95. You
|
|
can use each row's oid field as a unique value. However, if you need
|
|
to dump and reload the database, you will be assigned new oid's.
|
|
There is no way to restore the original oids.
|
|
|
|
One valid way of doing this is to create a function:
|
|
|
|
create table my_oids (f1 int4);
|
|
insert into my_oids values (1);
|
|
create function new_oid () returns int4 as
|
|
'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
|
|
language 'sql';
|
|
|
|
then:
|
|
|
|
create table my_stuff (my_key int4, value text);
|
|
insert into my_stuff values (new_oid(), 'hello');
|
|
|
|
However, keep in mind there is a race condition here where one
|
|
server could do the update, then another one do an update, and
|
|
they both could select the same new id. This statement should
|
|
be performed within a transaction.
|
|
|
|
3.24) How do I create a multi-column index?
|
|
|
|
You can not directly create a multi-column index using create index.
|
|
You need to define a function which acts on the multiple columns, then
|
|
use create index with that function.
|
|
|
|
3.25) What are the temp_XXX files in my database directory?
|
|
|
|
They are temp_ files generated by the query executor. For example,
|
|
if a sort needs to be done to satisfy an ORDER BY, some temp files are
|
|
generated as a result of the sort.
|
|
|
|
If you have no transactions or sorts running at the time, it is safe to
|
|
delete the temp_ files.
|
|
|
|
3.26) Why are my table files not getting any smaller after a delete?
|
|
|
|
If you run vacuum, unused rows will be marked for reuse, but the file
|
|
blocks are not released. We could move the unused rows to the end of
|
|
the file and use ftruncate() to decrease the file size, but no one has
|
|
implemented this yet.
|
|
|
|
3.27) Why can't I connect to my database from another machine?
|
|
|
|
The default configuration allows only connections from tcp/ip host
|
|
localhost. You need to add a host entry to the file
|
|
postgres95/data/pg_hba.
|
|
|
|
3.28) I get the error 'default index class unsupported' when creating an
|
|
index. How do I do it?
|
|
|
|
You probably used:
|
|
|
|
create index idx1 on person using btree (name);
|
|
|
|
Postgres95 indexes are extensible, and therefore you must specify a
|
|
class_type when creating an index. Read the manual page for create
|
|
index (called create_index).
|
|
|
|
3.29) Why does creating an index crash the backend server?
|
|
|
|
You have probably defined an incorrect *_ops type class for the field
|
|
you are indexing.
|
|
|
|
3.30) How do I specify a decimal constant as a float8, or a string as a text?
|
|
|
|
Use the :: operator. It is needed only when the default promotion
|
|
rules fail. i.e.:
|
|
|
|
insert into tab1 values (4.23::float8, '2343'::text)
|
|
|
|
3.31) How do I find out what indexes or operations are defined in the
|
|
database?
|
|
|
|
Run the file postgres95/src/tutorial/syscat.source. It illustrates
|
|
many of the 'select's needed to get information out of the database
|
|
system tables.
|
|
|
|
3.32) My database is corrupt. I can't do anything. What should I do?
|
|
|
|
The 1.02 release has a README file and utility that describes a
|
|
possible cause of the problem and a workaround. See the file
|
|
postgres95/contrib/zap_ltv/README for more information. Also
|
|
please contact the README author to help generate a complete
|
|
fix for this bug.
|
|
|
|
This bug may be fixed in 1.02.
|
|
|
|
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
|
|
|
|
Release 1.02 does not have this problem.
|
|
|
|
The 1.01 release of postgres95 uses a variable called PAGER to
|
|
filter the output of SELECT statements. Unfortunately, this
|
|
PAGER is used even when the standard output is not a terminal.
|
|
Upgrade to 1.02, due out August 1996, or undefine your PAGER
|
|
variable. There is also a patch located in the July archives of
|
|
the mailing list that fixes this problem on 1.01.
|
|
|
|
3.34) Why does 'createuser' return 'unexpected last match in input()'?
|
|
|
|
You have compile postgres with flex version 2.5.3. There is bug
|
|
in this version of flex. Use flex version 2.5.2 instead. There
|
|
is a doc/README.flex file which will properly patch the flex 2.5.3
|
|
source code.
|
|
|
|
3.35) All my servers crash under concurrent table access. Why?
|
|
|
|
This problem can be caused by a kernel that is not configured to
|
|
support semaphores.
|
|
|
|
3.36) What tools are available for hooking postgres to Web pages?
|
|
|
|
For web integration, PHP/FI is an excellent interface. The URL for
|
|
that is http://www.vex.net/php/
|
|
|
|
PHP is great for simple stuff, but for more complex stuff, some
|
|
still use the perl interface and CGI.pm.
|
|
|
|
An example of using WWW with C to talk to Postgres is can be
|
|
tried at:
|
|
|
|
http://www.ki.net/~mlc
|
|
|
|
3.37) What is the time-warp feature and how does it relate to vacuum?
|
|
|
|
Postgres95 handles data changes differently than most database
|
|
systems. When a row is changed in a table, the original row
|
|
is marked with the time it was changed, and a new row is created
|
|
with the current data. By default, only current rows are used
|
|
in a table. If you specify a date/time after the table name in
|
|
a FROM clause, you can access the data that was current at that
|
|
time, i.e.
|
|
|
|
SELECT *
|
|
FROM employees ['July 24, 1996 09:00:00']
|
|
|
|
displays employee rows in the table at the specified time.
|
|
You can specify intervals like [date,date], [date,], [,date],
|
|
or [,]. This last option accesses all rows that ever existed.
|
|
|
|
INSERTed rows get a timestamp too, so rows that were not in
|
|
the table at the desired time will not appear.
|
|
|
|
Vacuum removes rows that are no longer current. This time-warp
|
|
feature is used by the engine for rollback and crash recovery.
|
|
|
|
3.38) How do I tune the database engine for better performace?
|
|
|
|
There are two things that can be done. You can use Openlink's
|
|
option to disable fsync() by starting the postmaster with a
|
|
'-o -F' option. This will prevent fsync()'s from flushing to
|
|
disk after every transaction.
|
|
|
|
You can also use the postmaster -B option to increase the number
|
|
of shared memory buffers shared among the backend processes. If
|
|
you make this parameter too high, the process will not start or
|
|
crash unexpectedly. Each buffer is 8K and the defualt is 64
|
|
buffers.
|
|
|
|
|
|
|
|
----------------------------------------------------------------------
|
|
Section 4: Extending Postgres95
|
|
----------------------------------------------------------------------
|
|
|
|
4.1) I wrote a user-defined function and when I run it in psql, it
|
|
dumps core.
|
|
|
|
The problem could be a number of things. Try testing your
|
|
user-defined function in a stand alone test program first.
|
|
Also, make sure you are not sending elog NOTICES when the front-end
|
|
is expecting data, such as during a type_in() or type_out()
|
|
functions
|
|
|
|
4.2) I get messages of the type
|
|
NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!
|
|
|
|
You are pfree'ing something that was not palloc'ed. When writing
|
|
user-defined functions, do not include the file
|
|
"libpq-fe.h". Doing so will cause your palloc to be a malloc
|
|
instead of a free. Then, when the backend pfrees the storage,
|
|
you get the notice message.
|
|
|
|
4.3) I've written some nifty new types and functions for Postgres95.
|
|
|
|
Please share them with other postgres95 users. Send your
|
|
extensions to mailing list, and they will eventually end up in
|
|
the contrib/ subdirectory.
|
|
|
|
4.4) How do I write a C function to return a tuple?
|
|
|
|
This requires extreme wizardry, so extreme that the authors
|
|
have not ever tried it, though in principle it can be done.
|
|
The short answer is ... you can't. This capability is
|
|
forthcoming in the future.
|
|
|
|
----------------------------------------------------------------------
|
|
Section 5: Bugs
|
|
----------------------------------------------------------------------
|
|
|
|
5.1) How do I find out about bug fixes?
|
|
|
|
The directory ftp.ki.net:/pub/postgres95 contains patches for
|
|
the latest release.
|
|
|
|
5.2) How do I make a bug report?
|
|
|
|
First, check to see that your bug is not one that has already
|
|
been fixed (question 5.1). Then, fill out the "bug-template"
|
|
file and send it to:
|
|
|
|
pg95-dev@ki.net
|
|
|
|
This is the address of the developers mailing list.
|
|
|