mirror of
https://github.com/postgres/postgres.git
synced 2025-07-27 12:41:57 +03:00
Support Docs & Contrib
This commit is contained in:
Marc G. Fournier
827
doc/FAQ
Normal file
827
doc/FAQ
Normal file
@ -0,0 +1,827 @@
|
||||
==================================================
|
||||
Frequently Asked Questions (FAQ) for Postgres95
|
||||
==================================================
|
||||
last updated: Sun Aug 11 01:35:34 EDT 1996
|
||||
|
||||
current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
|
||||
original author: Jolly Chen (jolly@cs.berkeley.edu)
|
||||
|
||||
changes in this version (* = modified, + = new):
|
||||
* 1.8) What documentation is available for Postgres95?
|
||||
* 3.13) What is the maximum size for a tuple?
|
||||
* 3.14) I defined indices but my queries don't seem to make use of them. Why?
|
||||
* 3.37) What is the time-warp feature and how does it relate to vacuum?
|
||||
+ 3.38) How do I tune the database engine for better performace?
|
||||
|
||||
This file is divided approximately as follows:
|
||||
1.*) General questions
|
||||
2.*) Installation questions
|
||||
3.*) Postgres95 Features questions
|
||||
4.*) Questions about extending Postgres95
|
||||
5.*) Bugs
|
||||
|
||||
Questions answered:
|
||||
1.1) What is Postgres95?
|
||||
1.2) What does Postgres95 run on?
|
||||
1.3) Where can I get Postgres95?
|
||||
1.4) What's the copyright on Postgres95?
|
||||
1.5) Support for Postgres95
|
||||
1.6) Future releases of Postgres95
|
||||
1.7) Is there a commercial version of Postgres95?
|
||||
1.9) What version of SQL does Postgres95 use?
|
||||
1.10) Does Postgres95 work with databases from earlier versions of postgres?
|
||||
1.11) How many people use Postgres95?
|
||||
2.1) I get the error "cpp: command not found" when I try to compile
|
||||
2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
|
||||
2.3) initdb doesn't run
|
||||
2.4) when I start up the postmaster, I get
|
||||
2.5) The system seems to be confused about commas, decimal points, and
|
||||
2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
|
||||
2.7) The backend compiled successfully, but compiling libpq resulted
|
||||
in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
|
||||
2.8) Where can I find the bug fixes for postgres95?
|
||||
2.9) I can't apply the patches even though everything looks like it should
|
||||
work.
|
||||
2.10) When I run postmaster, I get a Bad System Call core dumped message.
|
||||
2.11) I get the error message "obj/fmgr.h: No such file or directory"
|
||||
2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
|
||||
2.13) I get the strange make errors right at the beginning:
|
||||
2.14) I have changed a source file, but a recompile does not see the
|
||||
3.1) How do I specify a KEY or other constraints on a column?
|
||||
3.2) Does Postgres95 support nested subqueries?
|
||||
3.3) How do I define a unique indices?
|
||||
3.4) I've having a lot of problems with using rules.
|
||||
3.5) I can't seem to write into the middle of large objects reliably.
|
||||
3.6) Does postgres95 have a graphical user interface? A report
|
||||
3.7) How can I write client applications to Postgres95?
|
||||
3.8) How do I prevent other hosts from accessing my Postgres95
|
||||
3.9) How do I set up a pg_group?
|
||||
3.10) What is the exact difference between binary cursors and normal cursors?
|
||||
3.11) Why doesn't the != operator work?
|
||||
3.12) What is a R-tree index and what is it used for?
|
||||
3.13) What is the maximum size for a tuple?
|
||||
3.14) I defined indices but my queries don't seem to make use of them. Why?
|
||||
3.15) Are there ODBC drivers for Postgres95?
|
||||
3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
|
||||
3.17) How do I do regular expression searches? case-insensitive
|
||||
regexp searching?
|
||||
3.18) I can't access the database as the 'root' user.
|
||||
3.19) I experienced a server crash during a vacuum. How do I remove the
|
||||
lock file?
|
||||
3.20) What is the difference between the various character types?
|
||||
3.21) In a query, how do I detect if a field is NULL?
|
||||
3.22) How do I see how the query optimizer is evaluating my query?
|
||||
3.23) How do I create a serial field?
|
||||
3.24) How do I create a multi-column index?
|
||||
3.25) What are the temp_XXX files in my database directory?
|
||||
3.26) Why are my table files not getting any smaller after a delete?
|
||||
3.27) Why can't I connect to my database from another machine?
|
||||
3.28) I get the error 'default index class unsupported' when creating an
|
||||
index. How do I do it?
|
||||
3.29) Why does creating an index crash the backend server?
|
||||
3.30) How do I specify a decimal constant as a float8, or a string as a text?
|
||||
3.31) How do I find out what indexes or operations are defined in the
|
||||
database?
|
||||
3.32) My database is corrupt. I can't do anything. What should I do?
|
||||
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
|
||||
3.34) Why does 'createuser' return 'unexpected last match in input()'?
|
||||
3.35) All my servers crash under concurrent table access. Why?
|
||||
3.36) What tools are available for hooking postgres to Web pages?
|
||||
3.37) What is the time-warp feature and how does it relate to vacuum?
|
||||
3.38) How do I tune the database engine for better performace?
|
||||
4.1) I wrote a user-defined function and when I run it in psql, it
|
||||
dumps core.
|
||||
4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0
|
||||
4.3) I've written some nifty new types and functions for Postgres95.
|
||||
4.4) How do I write a C function to return a tuple?
|
||||
5.1) How do I find out about bug fixes?
|
||||
5.2) How do I make a bug report?
|
||||
|
||||
|
||||
----------------------------------------------------------------------
|
||||
Section 1: General Questions
|
||||
----------------------------------------------------------------------
|
||||
|
||||
1.1) What is Postgres95?
|
||||
|
||||
Postgres95 is an enhancement of the POSTGRES database
|
||||
management system, a next-generation DBMS research prototype.
|
||||
While Postgres95 retains the powerful data model and rich data
|
||||
types of POSTGRES, it replaces the PostQuel query language with an
|
||||
extended subset of SQL. Postgres95 is free and the complete
|
||||
source is available.
|
||||
|
||||
Postgres95 development is being performed by a team of Internet
|
||||
developers who all subscribe to the Postgres95 development mailing
|
||||
list. The current coordinator is Marc G. Fournier (scrappy@ki.net).
|
||||
(See below on how to join). This team is now responsible for all
|
||||
current and future development of Postgres95.
|
||||
|
||||
The authors of Postgres95 1.01 were Andrew Yu and Jolly Chen.
|
||||
Many others have contributed to the porting, testing, debugging and
|
||||
enhancement of the code. The original Postgres code, from which
|
||||
Postgres95 is derived, was the effort of many graduate
|
||||
students, undergraduate students, and staff programmers
|
||||
working under the direction of Professor Michael Stonebraker
|
||||
at the University of California, Berkeley.
|
||||
|
||||
1.2) What does Postgres95 run on?
|
||||
|
||||
The authors have compiled and tested Postgres95 on the following
|
||||
platforms(some of these compiles require gcc 2.7.0):
|
||||
|
||||
- DEC Alpha AXP on OSF/1 2.0
|
||||
- HP PA-RISC on HP-UX 9.0
|
||||
- i386 Solaris
|
||||
- SUN SPARC on Solaris 2.4
|
||||
- SUN SPARC on SunOS 4.1.3
|
||||
- DEC MIPS on Ultrix 4.4
|
||||
- Intel x86 on Linux 1.2 and Linux ELF
|
||||
- OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
|
||||
- IBM on AIX 3.2.5
|
||||
- BSD/OS 2.0, 2.01 & 2.1
|
||||
- SGI MIPS on IRIX 5.3
|
||||
|
||||
The following ports are bundled with the Postgres95 distribution. The
|
||||
authors do not have handy access to these platforms but the
|
||||
ports have been tested by the others.
|
||||
|
||||
- Motorola MC68K or Intel x86 on NeXTSTEP 3.2
|
||||
- Intel x86 on Intel SVR4
|
||||
|
||||
1.3) Where can I get Postgres95?
|
||||
|
||||
The primary anonymous ftp site for postgres95 is:
|
||||
|
||||
ftp://ftp.ki.net/pub/postgres95
|
||||
|
||||
A mirror site exists at:
|
||||
|
||||
ftp://postgres95.vnet.net/pub/postgres95
|
||||
|
||||
1.4) What's the copyright on Postgres95?
|
||||
|
||||
Postgres95 is subject to the following COPYRIGHT.
|
||||
|
||||
POSTGRES95 Data Base Management System
|
||||
|
||||
Copyright (c) 1994-6 Regents of the University of California
|
||||
|
||||
Permission to use, copy, modify, and distribute this software and its
|
||||
documentation for any purpose, without fee, and without a written agreement
|
||||
is hereby granted, provided that the above copyright notice and this
|
||||
paragraph and the following two paragraphs appear in all copies.
|
||||
|
||||
IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
|
||||
DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
|
||||
LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS
|
||||
DOCUMENTATION, EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE
|
||||
POSSIBILITY OF SUCH DAMAGE.
|
||||
|
||||
THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
|
||||
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
|
||||
AND FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
|
||||
ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO
|
||||
PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
|
||||
|
||||
1.5) Support for Postgres95
|
||||
|
||||
There is no official support for Postgres95 from the original
|
||||
maintainers or from University of California, Berkeley. It is
|
||||
maintained through volunteer effort only.
|
||||
|
||||
With the generosity of the Jason Wright and others at Vnet,
|
||||
the postgres95 mailing list now has a new home --
|
||||
postgres95@postgres95.vnet.net. It is available for
|
||||
discussion of matters pertaining to Postgres95, including but
|
||||
not limited to bug reports and fixes. For info on how to
|
||||
subscribe, send a mail with the lines in the body (not the
|
||||
subject line):
|
||||
help
|
||||
info postgres95
|
||||
to
|
||||
majordomo@postgres95.vnet.net
|
||||
|
||||
There is also a digest list available. To subscribe to this list,
|
||||
send email to majordomo@postgres95.vnet.net with a BODY of:
|
||||
subscribe postgres95-digest
|
||||
Digests are sent out to members of this list whenever the main list has
|
||||
received around 30k of messages.
|
||||
|
||||
Archives and digests of the new mailing list at Vnet can be found at:
|
||||
ftp://postgres95.vnet.net/pub/postgres95/archives
|
||||
ftp://postgres95.vnet.net/pub/postgres95/digests
|
||||
|
||||
There is also a developers mailing list available. To subscribe to
|
||||
this list, send email to pg95-dev-request@ki.net with a BODY of:
|
||||
|
||||
subscribe pg95-dev
|
||||
|
||||
Additional information about Postgres95 can be found via the
|
||||
postgres95 WWW home page at:
|
||||
http://www.ki.net/postgres95
|
||||
|
||||
1.6) Future releases of Postgres95
|
||||
|
||||
The latest release of postgres95 is version 1.02.
|
||||
|
||||
1.7) Is there a commercial version of Postgres95?
|
||||
|
||||
Illustra Information Technology (a wholly owned subsidiary of
|
||||
Informix Software, Inc.) sells an object-relational
|
||||
DBMS called Illustra that was originally based on postgres.
|
||||
Illustra has cosmetic similarities to postgres95 but has more
|
||||
features, is more robust, performs better, and offers real
|
||||
documentation and support. On the flip side, it costs money.
|
||||
For more information, contact sales@illustra.com
|
||||
|
||||
1.8) What documentation is available for Postgres95?
|
||||
|
||||
A user manual, manual pages, and some small test examples
|
||||
are included in the distribution. The www page contains
|
||||
pointers to an implementation guide and five papers written
|
||||
about postgres design concepts and features.
|
||||
|
||||
1.9) What version of SQL does Postgres95 use?
|
||||
|
||||
Postgres95 supports a subset of SQL-92. It has most of the
|
||||
important constructs but lacks some of the functionality.
|
||||
The most visible differences are:
|
||||
- no support for primary keys or column constraints
|
||||
- no support for nested subqueries
|
||||
- no HAVING clause under a GROUP BY
|
||||
|
||||
On the other hand, you get to create user-defined types,
|
||||
functions, inheritance etc. If you're willing to help with
|
||||
postgres95 coding, eventually we can also add the missing
|
||||
features listed above.
|
||||
|
||||
1.10) Does Postgres95 work with databases from earlier versions of postgres?
|
||||
|
||||
Postgres95 v1.02 is compatible with databases created with v1.01.
|
||||
Those upgrading from 1.0 to 1.02 should read the directions in the
|
||||
MIGRATION_1.0_TO_1.02 directory.
|
||||
|
||||
1.11) How many people use Postgres95?
|
||||
|
||||
Since we don't have any licensing or registration scheme, it's
|
||||
impossible to tell. We do know hundreds copies of postgres95
|
||||
v1.* have been downloaded, and that there many hundreds of
|
||||
subscribers to the mailing lists.
|
||||
|
||||
----------------------------------------------------------------------
|
||||
Section 2: Installation Questions
|
||||
----------------------------------------------------------------------
|
||||
|
||||
2.1) I get the error "cpp: command not found" when I try to compile
|
||||
the backend.
|
||||
|
||||
Edit the src/backend/utils/Gen_fmgrtab.sh script to include the path
|
||||
for the cpp for your particular site.
|
||||
|
||||
2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
|
||||
|
||||
Use a more recent version of flex, version 2.5.2. Version 2.5.3
|
||||
has a known bug.
|
||||
|
||||
2.3) initdb doesn't run
|
||||
|
||||
* check to see that you have the proper paths set
|
||||
* check that the 'postgres' user owns all the right files
|
||||
* ensure that there are files in $PGDATA/files, and that they
|
||||
are non-empty. If they aren't, then "gmake install" failed for
|
||||
some reason
|
||||
|
||||
2.4) when I start up the postmaster, I get
|
||||
"FindBackend: could not find a backend to execute..."
|
||||
"postmaster: could not find backend to execute..."
|
||||
|
||||
You probably do not have the right path set up. the 'postgres'
|
||||
executable needs to be in your path.
|
||||
|
||||
2.5) The system seems to be confused about commas, decimal points, and
|
||||
date formats.
|
||||
|
||||
Check your locale configuration. postgres95 uses the locale
|
||||
settings of the user that ran the postmaster process. Set those
|
||||
accordingly for your operating environment.
|
||||
|
||||
2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
|
||||
|
||||
You need to manually edit the paths in src/Makefile.global to
|
||||
your site configuration.
|
||||
|
||||
2.7) The backend compiled successfully, but compiling libpq resulted
|
||||
in a complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
|
||||
|
||||
You've probably installed postgres95 somewhere other than
|
||||
/usr/local/postgres, but didn't edit the src/Makefile.global
|
||||
accordingly. See question 2.6.
|
||||
|
||||
2.8) Where can I find the bug fixes for postgres95?
|
||||
|
||||
The patches should be applied in the order listed. The patch files
|
||||
can be ftp'ed directly from the directory:
|
||||
ftp://ftp.ki.net/pub/postgres95
|
||||
|
||||
2.9) I can't apply the patches even though everything looks like it should
|
||||
work.
|
||||
|
||||
If you cut and paste directly off your web browser, tabs and
|
||||
whitespaces may not be preserved properly. Use the 'save as file'
|
||||
option from your web browser instead.
|
||||
|
||||
2.10) When I run postmaster, I get a Bad System Call core dumped message.
|
||||
|
||||
It could be a variety of problems, but first check to see that you
|
||||
have system V extensions installed on your kernel. Postgres95
|
||||
requires kernel support for shared memory.
|
||||
|
||||
2.11) I get the error message "obj/fmgr.h: No such file or directory"
|
||||
|
||||
This indicates that you did not generate the file fmgr.h
|
||||
properly. Something failed in the running of the
|
||||
src/backend/utils/Gen_fmgrtab.sh script. Check to see the
|
||||
paths used in that script is appropriate to your system.
|
||||
|
||||
2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
|
||||
|
||||
You either do not have shared memory configured properly in kernel
|
||||
or you need to enlarge the shared memory available in the kernel.
|
||||
The exact amount you need depends on your architecture and how
|
||||
many buffers you configure postmaster to run with. For most
|
||||
systems, with default buffer sizes, you need a minimum of ~760K.
|
||||
|
||||
2.13) I get the strange make errors right at the beginning:
|
||||
warning: NUL character seen; rest of line ignored
|
||||
*** missing separator. Stop.
|
||||
or
|
||||
Is a directory. Stop.
|
||||
|
||||
Eliminate any whitespaces at the end of the PORTNAME line in
|
||||
Makefile.global. Extraneous tabs or spaces will confuse the make
|
||||
templates.
|
||||
|
||||
2.14) I have changed a source file, but a recompile does not see the
|
||||
change?
|
||||
|
||||
The Makefiles do not have the proper dependencies. You have to
|
||||
do a 'make clean' and then another 'make'.
|
||||
|
||||
----------------------------------------------------------------------
|
||||
Section 3: Postgres95 Features
|
||||
----------------------------------------------------------------------
|
||||
|
||||
3.1) How do I specify a KEY or other constraints on a column?
|
||||
|
||||
Column constraints are not supported in postgres95.
|
||||
As a consequence, the system does not check for duplicates.
|
||||
|
||||
3.2) Does Postgres95 support nested subqueries?
|
||||
|
||||
Subqueries are not implemented, but they can be simulated using sql
|
||||
functions.
|
||||
|
||||
3.3) How do I define a unique indices?
|
||||
|
||||
Postgres95 does not support unique indices. Defining an index does
|
||||
not preclude insertion of duplicate index key values.
|
||||
|
||||
3.4) I've having a lot of problems with using rules.
|
||||
|
||||
Currently, the rule system in postgres95 is mostly broken. It
|
||||
works enough to support the view mechanism, but that's about it. Use
|
||||
postgres95 rules at your own peril.
|
||||
|
||||
3.5) I can't seem to write into the middle of large objects reliably.
|
||||
|
||||
The Inversion large object system in postgres95 is also
|
||||
mostly broken. It works well enough for storing large wads
|
||||
of data and reading them back out, but the implementation has
|
||||
some underlying problems. Use postgres95 large objects at
|
||||
your own peril.
|
||||
|
||||
3.6) Does postgres95 have a graphical user interface? A report
|
||||
generator? A embedded query language interface?
|
||||
|
||||
No. No. No. Not in the official distribution at least. Some
|
||||
users have reported some success at using 'pgbrowse' and 'onyx' as
|
||||
frontends to postgres95. Several contributions are working on
|
||||
tk based frontend tools. Ask on the mailing list.
|
||||
|
||||
3.7) How can I write client applications to Postgres95?
|
||||
|
||||
Postgres95 supports a C-callable library interface called libpq
|
||||
as well as a Tcl-based library interface called libtcl.
|
||||
|
||||
Others have contributed a perl interface and a WWW gateway
|
||||
to postgres95. See the postgres95 home pages for more details.
|
||||
|
||||
3.8) How do I prevent other hosts from accessing my Postgres95
|
||||
backend?
|
||||
|
||||
Use host-based authentication by modifying the file
|
||||
$PGDATA/pg_hba accordingly.
|
||||
|
||||
3.9) How do I set up a pg_group?
|
||||
|
||||
Currently, there is no easy interface to set up user groups.
|
||||
You have to explicitly insert/update the pg_group table. For example:
|
||||
|
||||
jolly=> insert into pg_group (groname, grosysid, grolist)
|
||||
jolly=> values ('posthackers', '1234', '{5443, 8261}');
|
||||
INSERT 548224
|
||||
jolly=> grant insert on foo to group posthackers;
|
||||
CHANGE
|
||||
jolly=>
|
||||
|
||||
The fields in pg_group are:
|
||||
groname: the group name. This a char16 and should
|
||||
be purely alphanumeric. Do not include underscores
|
||||
or other punctuation.
|
||||
grosysid: the group id. This is an int4.
|
||||
This should be unique for each group.
|
||||
grolist: the list of pg_user id's that belong in the group.
|
||||
This is an int4[].
|
||||
|
||||
3.10) What is the exact difference between binary cursors and normal cursors?
|
||||
|
||||
Normal cursors return data back in ASCII format. Since data is stored
|
||||
natively in binary format, the system must do a conversion to produce
|
||||
the ASCII format. In addition, ASCII formats are often large in size
|
||||
than binary format. Once the attributes come back in ASCII, often the
|
||||
client application then has to convert it to a binary format to
|
||||
manipulate it anyway.
|
||||
|
||||
Binary cursors give you back the data in the native binary
|
||||
representation. Thus, binary cursors will tend to be a little faster
|
||||
since there's less overhead of conversion.
|
||||
|
||||
However, ASCII is architectural neutral whereas binary representation
|
||||
can differ between different machine architecture. Thus, if your client
|
||||
machine uses a different representation than you server machine, getting
|
||||
back attributes in binary format is probably not what you want. Also,
|
||||
if your main purpose is displaying the data in ASCII, then getting it
|
||||
back in ASCII will save you some effort on the client side.
|
||||
|
||||
3.11) Why doesn't the != operator work?
|
||||
|
||||
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.
|
||||
|
||||
Reference in New Issue
Block a user