1998-02-27 23:01:58 +01:00
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<TITLE>PostgreSQL FAQ</title>
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<H1>
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1998-02-18 16:56:06 +01:00
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Frequently Asked Questions (FAQ) for PostgreSQL
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</H1>
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<P>
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Last updated: Wed Feb 25 14:37:07 EST 1998
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<P>
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Current maintainer: Bruce Momjian (<a
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href="mailto:maillist@candle.pha.pa.us">maillist@candle.pha.pa.us</a>)<BR>
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<P>
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The most recent version of this document can be viewed at
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the postgreSQL Web site, <a
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href="http://postgreSQL.org">http://postgreSQL.org</a>.
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<P>
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1998-02-18 16:56:06 +01:00
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Linux-specific questions are answered in
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1998-02-27 23:01:58 +01:00
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<a href="http://postgreSQL.org/docs/faq-linux.shtml">http://postgreSQL.org/docs
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/faq-linux.shtml</a>.
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<P>
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1998-02-18 16:56:06 +01:00
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Irix-specific questions are answered in
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1998-02-27 23:01:58 +01:00
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<a href="http://postgreSQL.org/docs/faq-irix.shtml">http://postgreSQL.org/docs/
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faq-irix.shtml</a>.
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<P>
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<HR>
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<P>
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<H2>Questions answered:</H2>
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<H3> 1) General questions</H3>
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<a href="#1.1">1.1</a>) What is PostgreSQL?<BR>
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<a href="#1.2">1.2</a>) What does PostgreSQL run on?<BR>
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<a href="#1.3">1.3</a>) Where can I get PostgreSQL?<BR>
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<a href="#1.4">1.4</a>) What's the copyright on PostgreSQL?<BR>
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<a href="#1.5">1.5</a>) Support for PostgreSQL<BR>
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<a href="#1.6">1.6</a>) Latest release of PostgreSQL<BR>
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<a href="#1.7">1.7</a>) Is there a commercial version of PostgreSQL?<BR>
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<a href="#1.8">1.8</a>) What documentation is available for PostgreSQL?<BR>
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<a href="#1.9">1.9</a>) What version of SQL does PostgreSQL use?<BR>
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<a href="#1.10">1.10</a>) Does PostgreSQL work with databases from
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earlier versions of postgres?<BR>
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<a href="#1.11">1.11</a>) Are there ODBC drivers for
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PostgreSQL?<BR>
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<a href="#1.12">1.12</a>) What tools are available for hooking
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postgres to Web pages?<BR>
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<a href="#1.13">1.13</a>) Does PostgreSQL have a graphical user interface
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?
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A report generator? A embedded query language interface?<BR>
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<a href="#1.14">1.14</a>) What is a good book to learn SQL?<BR>
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<H3> 2) Installation/Configuration questions</H3>
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<a href="#2.1">2.1</a>) initdb doesn't run<BR>
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<a href="#2.2">2.2</a>) 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..."<BR>
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<a href="#2.3">2.3</a>) The system seems to be confused about commas,
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decimal points, and date formats.<BR>
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<a href="#2.4">2.4</a>) How do I install PostgreSQL somewhere other than
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/usr/local/pgsql?<BR>
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<a href="#2.5">2.5</a>) When I run postmaster, I get a Bad System Call
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core dumped message.<BR>
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<a href="#2.6">2.6</a>) When I try to start the postmaster, I get
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IpcMemoryCreate errors.<BR>
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<a href="#2.7">2.7</a>) I have changed a source file, but a
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recompile does not see the change?<BR>
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<a href="#2.8">2.8</a>) How do I prevent other hosts from accessing my
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PostgreSQL<BR>
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<a href="#2.9">2.9</a>) I can't access the database as the
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'root' user.<BR>
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<a href="#2.10">2.10</a>) All my servers crash under concurrent
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table access. Why?<BR>
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<a href="#2.11">2.11</a>) How do I tune the database engine for
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better performance?<BR>
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<a href="#2.12">2.12</a>) What debugging features are available in
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PostgreSQL?<BR>
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<a href="#2.13">2.13</a>) How do I enable more than 32 concurrent
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backends?
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<H3> 3) Operational questions</H3>
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<a href="#3.1">3.1</a>) Does PostgreSQL support nested subqueries?<BR>
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<a href="#3.2">3.2</a>) I've having a lot of problems using rules.<BR>
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<a href="#3.3">3.3</a>) I can't seem to write into the middle of large
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objects reliably.<BR>
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<a href="#3.4">3.4</a>) How can I write client applications to
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PostgreSQL?<BR>
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<a href="#3.5">3.5</a>) How do I set up a pg_group?<BR>
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<a href="#3.6">3.6</a>) What is the exact difference between
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binary cursors and normal cursors?<BR>
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<a href="#3.7">3.7</a>) What is a R-tree index and what is it
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used for?<BR>
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<a href="#3.8">3.8</a>) What is the maximum size for a
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tuple?<BR>
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<a href="#3.9">3.9</a>) I defined indices but my queries don't
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seem to make use of them. Why?<BR>
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<a href="#3.10">3.10</a>) How do I do regular expression searches?
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case-insensitive regexp searching?<BR>
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<a href="#3.11">3.11</a>) I experienced a server crash during a
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vacuum. How do I remove the lock file?<BR>
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<a href="#3.12">3.12</a>) What is the difference between the
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various character types?<BR>
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<a href="#3.13">3.13</a>) In a query, how do I detect if a field
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is NULL?<BR>
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<a href="#3.14">3.14</a>) How do I see how the query optimizer is
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evaluating my query?<BR>
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<a href="#3.15">3.15</a>) How do I create a serial field?<BR>
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<a href="#3.16">3.16</a>) What are the pg_psort.XXX files in my
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database directory?<BR>
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<a href="#3.17">3.17</a>) Why can't I connect to my database from
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another machine?<BR>
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<a href="#3.18">3.18</a>) How do I find out what indexes or
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operations are defined in the database?<BR>
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<a href="#3.19">3.19</a>) What is the time-warp feature and how
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does it relate to vacuum?<BR>
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<a href="#3.20">3.20</a>) What is an oid? What is a tid?<BR>
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<a href="#3.21">3.21</a>) What is the meaning of some of the terms
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used in Postgres?<BR>
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<a href="#3.22">3.22</a>) What is Genetic Query Optimization?<BR>
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<a href="#3.23">3.23</a>) How do you remove a column from a table?<BR>
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<a href="#3.24">3.24</a>) How do SELECT only the first few rows of
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a query?<BR>
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<a href="#3.25">3.25</a>) Why can't I create a column named "time"?<BR>
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<a href="#3.26">3.26</a>) How much database disk space is required
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to store data from a typical flat file?<BR>
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<H3> 4) Questions about extending PostgreSQL</H3>
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<a href="#4.1">4.1</a>) I wrote a user-defined function and when I run
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it in psql, it dumps core.<BR>
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<a href="#4.2">4.2</a>) I get messages of the type
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NOTICE:PortalHeapMemoryFree: 0x402251d0<BR>
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<a href="#4.3">4.3</a>) I've written some nifty new types and functions
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for PostgreSQL.<BR>
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<a href="#4.4">4.4</a>) How do I write a C function to return a
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tuple?<BR>
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<H3> 5) Bugs</H3>
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<a href="#5.1">5.1</a>) How do I make a bug report?
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<P>
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<HR>
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<H2> Section 1: General Questions</H2> <H3><a
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name="1.1">1.1</a>) What is PostgreSQL?</H3>
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<P>
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PostgreSQL is an enhancement of the POSTGRES database management system,
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a next-generation DBMS research prototype. While PostgreSQL retains the
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1998-02-18 16:56:06 +01:00
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powerful data model and rich data types of POSTGRES, it replaces the
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PostQuel query language with an extended subset of SQL. PostgreSQL is
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free and the complete source is available.
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<P>
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PostgreSQL development is being performed by a team of Internet
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developers who all subscribe to the PostgreSQL development mailing list.
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The current coordinator is Marc G. Fournier (<a
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href="mailto:scrappy@postgreSQL.org">scrappy@postgreSQL.org</a>). (See
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below on how to join). This team is now responsible for all current and
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future development of PostgreSQL.
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<P>
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The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many
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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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PostgreSQL is derived, was the effort of many graduate students,
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undergraduate students, and staff programmers working under the
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direction of Professor Michael Stonebraker at the University of
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California, Berkeley.
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<P>
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The original name of the software at Berkeley was Postgres. When SQL
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functionality was added in 1995, its name was changed to Postgres95. The
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name was changed at the end of 1996 to PostgreSQL.
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1998-02-27 23:01:58 +01:00
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<P>
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<H3><a name="1.2">1.2</a>) What does PostgreSQL run
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on?</H3>
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<P>
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The authors have compiled and tested PostgreSQL on the following
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platforms(some of these compiles require gcc 2.7.0):
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<UL>
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<LI> aix - IBM on AIX 3.2.5 or 4.x
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<LI> alpha - DEC Alpha AXP on Digital Unix 2.0, 3.2, 4.0
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<LI> BSD44_derived - OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
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<LI> bsdi - BSD/OS 2.0, 2.01, 2.1, 3.0
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<LI> dgux - DG/UX 5.4R4.11
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<LI> hpux - HP PA-RISC on HP-UX 9.0, 10
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<LI> i386_solaris - i386 Solaris
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<LI> irix5 - SGI MIPS on IRIX 5.3
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<LI> linux - Intel x86 on Linux 2.0 and Linux ELF
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SPARC on Linux ELF
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PPC on Linux Elf
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(For non-ELF Linux, see LINUX_ELF below).
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<LI> sco - SCO 3.2v5
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<LI> sparc_solaris - SUN SPARC on Solaris 2.4, 2.5, 2.5.1
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<LI> sunos4 - SUN SPARC on SunOS 4.1.3
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<LI> svr4 - Intel x86 on Intel SVR4 and MIPS
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<LI> ultrix4 - DEC MIPS on Ultrix 4.4
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</UL>
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The following platforms have known problems/bugs:
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<UL>
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<LI> nextstep - Motorola MC68K or Intel x86 on NeXTSTEP 3.2
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</UL>
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<P>
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<H3><a name="1.3">1.3</a>) Where can I get PostgreSQL?</H3>
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<P> The primary anonymous ftp site for PostgreSQL is:
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<UL>
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<LI> <a
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href="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</a>
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</UL>
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<P> A mirror site exists at:
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<UL>
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<LI> <a
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href="ftp://postgres95.vnet.net/pub/postgres95">ftp://postgres95.vnet.net/pub/p
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ostgres95</a>
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<LI> <a
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href="ftp://ftp.luga.or.at/pub/postgres95">ftp://ftp.luga.or.at/pub/postgres95<
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/a>
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<LI> <a
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href="ftp://cal011111.student.utwente.nl/pub/postgres95">ftp://cal011111.studen
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t.utwente.nl/pub/postgres95</a>
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<LI> <a
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href="ftp://ftp.uni-trier.de/pub/database/rdbms/postgres/postgres95">ftp://ftp.
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uni-trier.de/pub/database/rdbms/postgres/postgres95</a>
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<LI> <a
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href="ftp://rocker.sch.bme.hu">ftp://rocker.sch.bme.hu</a>
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</UL>
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<H3><a name="1.4">1.4</a>) What's the copyright on
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PostgreSQL?</H3>
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<P>
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1998-02-18 16:56:06 +01:00
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PostgreSQL is subject to the following COPYRIGHT.
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<P>
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1998-02-18 16:56:06 +01:00
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PostgreSQL Data Base Management System
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1998-02-27 23:01:58 +01:00
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<P>
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1998-02-18 16:56:06 +01:00
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Copyright (c) 1994-6 Regents of the University of California
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<P>
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1998-02-18 16:56:06 +01:00
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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
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agreement is hereby granted, provided that the above copyright notice
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and this paragraph and the following two paragraphs appear in all
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copies.
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<P>
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IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY
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FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
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INCLUDING 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
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THE POSSIBILITY OF SUCH DAMAGE.
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<P>
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1998-02-18 16:56:06 +01:00
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THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
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1998-02-27 23:01:58 +01:00
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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
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IS ON AN "AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO
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OBLIGATIONS TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
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MODIFICATIONS.
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<P>
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<H3><a name="1.5">1.5</a>) Support for PostgreSQL </H3>
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<P>
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There is no official support for PostgreSQL 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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<P>
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The main mailing list is: <a
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href="mailto:questions@postgreSQL.org">questions@postgreSQL.org</a>. It
|
|
|
|
|
is available for discussion o f matters pertaining to PostgreSQL,
|
|
|
|
|
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)
|
|
|
|
|
<PRE>
|
|
|
|
|
<CODE>
|
1997-07-13 22:00:14 +02:00
|
|
|
subscribe
|
|
|
|
|
end
|
1998-02-27 23:01:58 +01:00
|
|
|
</CODE>
|
|
|
|
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</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
to <a
|
|
|
|
|
href="mailto:questions-request@postgreSQL.org">questions-request@postgreSQL.org
|
|
|
|
|
</a>.
|
|
|
|
|
<P>
|
|
|
|
|
There is also a digest list available. To subscribe to this list, send
|
|
|
|
|
email to:
|
|
|
|
|
<a
|
|
|
|
|
href="mailto:questions-digest-request@postgreSQL.org">
|
|
|
|
|
questions-digest-request@postgreSQL.org</a> with a BODY of:
|
|
|
|
|
<PRE>
|
|
|
|
|
<KBD>
|
1997-07-13 22:00:14 +02:00
|
|
|
subscribe
|
|
|
|
|
end
|
1998-02-27 23:01:58 +01:00
|
|
|
</KBD>
|
|
|
|
|
</PRE>
|
1998-02-18 16:56:06 +01:00
|
|
|
Digests are sent out to members of this list whenever the main list has
|
|
|
|
|
received around 30k of messages.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
There is a bugs mailing list available. To subscribe to this
|
|
|
|
|
list, send email to <a
|
|
|
|
|
href="mailto:bugs-request@postgreSQL.org">bugs-request@postgreSQL.org</a>
|
|
|
|
|
with a BODY of:
|
|
|
|
|
<P>
|
|
|
|
|
There is also a developers discussion mailing list available. To subscribe to
|
|
|
|
|
this
|
|
|
|
|
list, send email to <a
|
|
|
|
|
href="mailto:hackers-request@postgreSQL.org">hackers-request@postgreSQL.org</a>
|
|
|
|
|
with a BODY of:
|
|
|
|
|
<P>
|
|
|
|
|
<PRE>
|
|
|
|
|
<KBD>
|
1997-07-13 22:00:14 +02:00
|
|
|
subscribe
|
|
|
|
|
end
|
1998-02-27 23:01:58 +01:00
|
|
|
</KBD>
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
Additional information about PostgreSQL can be found via the PostgreSQL
|
|
|
|
|
WWW home page at:
|
|
|
|
|
<BLOCKQUOTE>
|
|
|
|
|
<a
|
|
|
|
|
href="http://postgreSQL.org">http://postgreSQL.org</a>
|
|
|
|
|
</BLOCKQUOTE>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.6">1.6</a>) Latest release of PostgreSQL</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
The latest release of PostgreSQL is version 6.2.1, which was released on
|
1998-02-27 23:01:58 +01:00
|
|
|
October 17th, 1997. We are testing 6.3 beta. For information about
|
|
|
|
|
what is new in 6.3, see our TODO list on our WWW page.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
We plan to have major releases every three months.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.7">1.7</a>) Is there a commercial version of PostgreSQL?</H
|
|
|
|
|
3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
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
|
|
|
|
|
PostgreSQL but has more features, is more robust, performs better, and
|
1998-02-27 23:01:58 +01:00
|
|
|
offers real documentation and support. On the flip side, it costs
|
|
|
|
|
money. For more information, contact <a
|
|
|
|
|
href="mailto:sales@illustra.com">sales@illustra.com</a>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.8">1.8</a>) What documentation is available for PostgreSQL?
|
|
|
|
|
</H3>
|
|
|
|
|
<P>
|
|
|
|
|
A user manual, manual pages, and some small test examples are included
|
|
|
|
|
in the distribution. The sql and built-in manual pages are particularly
|
1998-02-18 16:56:06 +01:00
|
|
|
important.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
The www page contains pointers to an implementation guide and five
|
|
|
|
|
papers written about postgres design concepts and features.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.9">1.9</a>) What version of SQL does PostgreSQL use?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
PostgreSQL supports a subset of SQL-92. It has most of the important
|
|
|
|
|
constructs but lacks some of the functionality. The most visible
|
|
|
|
|
differences are:
|
|
|
|
|
<UL>
|
|
|
|
|
<LI> no HAVING clause under a GROUP BY
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
On the other hand, you get to create user-defined types, functions,
|
1998-02-27 23:01:58 +01:00
|
|
|
inheritance etc.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.10">1.10</a>) Does PostgreSQL work with databases from
|
|
|
|
|
earlier versions of postgres?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
PostgreSQL v1.09 is compatible with databases created with v1.01.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Upgrading to 6.3 from earlier releases requires a dump and restore.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Upgrading to 6.2.1 from pre-6.2 requires a dump and restore.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
Upgrading to 6.2.1 from 6.2 does not require a dump, but see the
|
|
|
|
|
appropriate /migration file in the distribution.
|
|
|
|
|
<P>
|
|
|
|
|
Those ugrading from versions earlier than 1.09 must upgrade to 1.09
|
|
|
|
|
first without a dump/reload, then dump the data from 1.09, and then load
|
|
|
|
|
it into 6.2.1 or 6.3 beta.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.11">1.11</a>) Are there ODBC drivers for PostgreSQL?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
There are two ODBC drivers available, PostODBC and OpenLink ODBC.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
PostODBC is included in the distribution.
|
|
|
|
|
For all people being interested in PostODBC, there are now two mailing
|
|
|
|
|
lists devoted to the discussion of PostODBC. The mailing lists are:
|
|
|
|
|
<UL>
|
|
|
|
|
<LI> <a
|
|
|
|
|
href="mailto:postodbc-users@listserv.direct.net">postodbc-users@listserv.direct
|
|
|
|
|
.
|
|
|
|
|
net</a>
|
|
|
|
|
<LI> <a
|
|
|
|
|
href="mailto:postodbc-developers@listserv.direct.net">postodbc-developers@lists
|
|
|
|
|
e
|
|
|
|
|
rv.direct.net</a>
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
|
|
|
|
these lists are ordinary majordomo mailing lists. You can subscribe by
|
1998-02-18 16:56:06 +01:00
|
|
|
sending a mail to:
|
1998-02-27 23:01:58 +01:00
|
|
|
<UL>
|
|
|
|
|
<LI> <a
|
|
|
|
|
href="mailto:majordomo@listserv.direct.net">majordomo@listserv.direct.net</a>
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
|
|
|
|
OpenLink ODBC is very popular. You can get it from <a
|
|
|
|
|
href="http://www.openlinksw.com/">
|
|
|
|
|
http://www.openlinksw.com/postgres.html</a>. It works with our standard
|
|
|
|
|
ODBC client software so you'll have Postgres ODBC available on every
|
|
|
|
|
client platform we support (Win, Mac, Unix, VMS).
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
We will probably be selling this product to people who need
|
1998-02-27 23:01:58 +01:00
|
|
|
commercial-quality support, but a freeware version will always be
|
|
|
|
|
available. Questions to <a
|
|
|
|
|
href="mailto:postgres95@openlink.co.uk">postgres95@openlink.co.uk</a>.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.12">1.12</a>) What tools are available for hooking
|
|
|
|
|
postgres to Web pages?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
A nice introduction to Database-backed Web pages can be seen at:
|
1998-02-27 23:01:58 +01:00
|
|
|
<a href="http://www.webtools.com">http://www.webtools.com</a>
|
|
|
|
|
<P>
|
|
|
|
|
For web integration, PHP is an excellent interface. The URL for that
|
|
|
|
|
is <a href="http://www.php.net">http://www.php.net</a>
|
|
|
|
|
<P>
|
|
|
|
|
PHP is great for simple stuff, but for more complex stuff, some still
|
|
|
|
|
use the perl interface and CGI.pm.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
An WWW gatway based on WDB using perl can be downloaded from:
|
1998-02-27 23:01:58 +01:00
|
|
|
<UL>
|
|
|
|
|
<LI>
|
|
|
|
|
<a
|
|
|
|
|
href="http://www.eol.ists.ca/~dunlop/wdb-p95">http://www.eol.ists.ca/~dunlop/wd
|
|
|
|
|
b
|
|
|
|
|
-p95</a>
|
|
|
|
|
</UL>
|
|
|
|
|
<H3><a name="1.13">1.13</a>) Does PostgreSQL have a graphical user interface
|
|
|
|
|
?
|
|
|
|
|
A report generator? A embedded query language interface?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
We have a nice graphical user interface called pgaccess, which is
|
|
|
|
|
shipped as part of the distribtion. Pgaccess also has a report
|
|
|
|
|
generator.
|
|
|
|
|
<P>
|
|
|
|
|
We also have ecpg, which is an embedded SQL query language interface for
|
|
|
|
|
C. This is also included.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="1.14">1.14</a>) What is a good book to learn SQL?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Many of our users like <I>The Practical SQL Handbook</I>,
|
|
|
|
|
Bowman et al, Addison Wesley.
|
|
|
|
|
<P>
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
<H2> Section 2: Installation Questions
|
|
|
|
|
</H2>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.1">2.1</a>) initdb doesn't run</H3>
|
|
|
|
|
<P>
|
|
|
|
|
<UL>
|
|
|
|
|
<LI> check to see that you have the proper paths set
|
|
|
|
|
<LI> check that the 'postgres' user owns all the right files
|
|
|
|
|
<LI> 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
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.2">2.2</a>) when I start up the postmaster, I get
|
|
|
|
|
"FindBackend: could not find a backend to execute..."
|
|
|
|
|
"postmaster: could not find backend to execute..."</H3>
|
|
|
|
|
<P>
|
|
|
|
|
You probably do not have the right path set up. The 'postgres'
|
|
|
|
|
executable needs to be in your path.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.3">2.3</a>) The system seems to be confused about commas,
|
|
|
|
|
decimal points, and date formats.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Check your locale configuration. PostgreSQL uses the locale settings of
|
|
|
|
|
the user that ran the postmaster process. Set those accordingly for
|
|
|
|
|
your operating environment.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.4">2.4</a>) How do I install PostgreSQL somewhere other tha
|
|
|
|
|
n
|
|
|
|
|
/usr/local/pgsql?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You need to edit Makefile.global and change POSTGRESDIR accordingly, or
|
|
|
|
|
create a Makefile.custom and define POSTGRESDIR there.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.5">2.5</a>) When I run postmaster, I get a Bad System
|
|
|
|
|
Call core dumped message.</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
It could be a variety of problems, but first check to see that you have
|
|
|
|
|
system V extensions installed on your kernel. PostgreSQL requires kernel
|
|
|
|
|
support for shared memory.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.6">2.6</a>) When I try to start the postmaster, I get
|
|
|
|
|
IpcMemoryCreate errors.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.7">2.7</a>) I have changed a source file, but a
|
|
|
|
|
recompile does not see the change?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
The Makefiles do not have the proper dependencies for include files. You
|
|
|
|
|
have to do a 'make clean' and then another 'make'.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.8">2.8</a>) How do I prevent other hosts from accessing my
|
|
|
|
|
PostgreSQL backend?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
By default, PostgreSQL only allows connections from the local machine
|
|
|
|
|
using unix domain. You must add the -i flag to the postmaster, and
|
|
|
|
|
enable host-based authentication by modifying the file $PGDATA/pg_hba
|
1998-02-18 16:56:06 +01:00
|
|
|
accordingly.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.9">2.9</a>) I can't access the database as the 'root'
|
|
|
|
|
user.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.10">2.10</a>) All my servers crash under concurrent table
|
|
|
|
|
access. Why?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
This problem can be caused by a kernel that is not configured to support
|
|
|
|
|
semaphores.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.11">2.11</a>) How do I tune the database engine for
|
|
|
|
|
better performance?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
There are two things that can be done. You can disable fsync() by
|
|
|
|
|
starting the postmaster with a '-o -F' option. This
|
|
|
|
|
will prevent fsync()'s from flushing to disk after every transaction.
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
You can also use the postgres -S option to increase the maximum
|
|
|
|
|
amount of memory used by each backend process for temporary sorts.
|
|
|
|
|
Each buffer is 1K and the defualt is 512 buffers.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.12">2.12</a>) What debugging features are available in
|
|
|
|
|
PostgreSQL?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
PostgreSQL has several features that report status information that can
|
|
|
|
|
be valuable for debugging purposes.
|
|
|
|
|
<P>
|
|
|
|
|
First, by running configure with the -enable-cassert option,
|
|
|
|
|
many assert()'s monitor the progress of the backend and halt the
|
|
|
|
|
program when something unexpected occurs.
|
|
|
|
|
<P>
|
|
|
|
|
Both postmaster and postgres have several debug options available.
|
|
|
|
|
First, whenever you start the postmaster, make sure you send the
|
|
|
|
|
standard output and error to a log file, like:
|
|
|
|
|
<PRE>
|
|
|
|
|
<KBD>
|
1997-09-04 07:34:47 +02:00
|
|
|
cd /usr/local/pgsql
|
1998-02-27 23:01:58 +01:00
|
|
|
./bin/postmaster >server.log 2>&1 &
|
|
|
|
|
</KBD>
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
This will put a server.log file in the top-level PostgreSQL directory.
|
|
|
|
|
This file can contain useful information about problems or errors
|
|
|
|
|
encountered by the server. Postmaster has a -d option that allows even
|
|
|
|
|
more detailed information to be reported. The -d option takes a number
|
|
|
|
|
1-3 that specifies the debug level. Be warned that a debug level
|
|
|
|
|
of 3 generates large log files.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You can actuall run the postgres backend from the command line, and type
|
1998-02-27 23:01:58 +01:00
|
|
|
your SQL statement directly. This is recommended ONLY for debugging
|
|
|
|
|
purposes. Note that a newline terminates the query, not a semicolon. If
|
|
|
|
|
you have compiled with debugging symbols, you can use a debugger
|
|
|
|
|
to see what is happening. Because the backend was not started from the
|
|
|
|
|
postmaster, it is not running in an identical environment and
|
|
|
|
|
locking/backend interaction problems may not be duplicated. Some
|
|
|
|
|
operating system can attach to a running backend directly to diagnose
|
|
|
|
|
problems.
|
|
|
|
|
<P>
|
|
|
|
|
The postgres program has a -s, -A, -t options that can be very usefull
|
|
|
|
|
for debugging and performance measurements.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You can also compile with profiling to see what functions are taking
|
1998-02-27 23:01:58 +01:00
|
|
|
execution time. The backend profile files will be deposited in the
|
|
|
|
|
pgsql/data/base/dbname directory. The client profile file will be put
|
|
|
|
|
in the current directory.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
The EXPLAIN command (see this FAQ) allows you to see how PostgreSQL is
|
|
|
|
|
interpreting your query.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="2.13">2.13</a>) How do I enable more than 32 concurrent
|
|
|
|
|
backends?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Edit include/storage/sinvaladt.h, and change the value of MaxBackendId.
|
|
|
|
|
In the future, we plan to make this a configurable prameter.
|
|
|
|
|
<P>
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
<H2> Section 3: PostgreSQL Features
|
|
|
|
|
</H2>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.1">3.1</a>) Does PostgreSQL support nested subqueries?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Yes.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.2">3.2</a>) I've having a lot of problems using rules.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Currently, the rule system in PostgreSQL has some limitations. It works
|
|
|
|
|
enough to support the view mechanism, but does not handle
|
|
|
|
|
Insert/Update/Delete well.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.3">3.3</a>) I can't seem to write into the middle of large
|
|
|
|
|
objects reliably.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
The Inversion large object system now works perfectly. You should no
|
|
|
|
|
longer have problems with large objects.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.4">3.4</a>) How can I write client applications to PostgreS
|
|
|
|
|
QL?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
PostgreSQL supports a C-callable library interface called libpq as well
|
|
|
|
|
as many others. See the /src/interfaces directory.
|
|
|
|
|
<P>
|
|
|
|
|
Others have contributed a perl interface and a WWW gateway to
|
|
|
|
|
PostgreSQL. See the PostgreSQL home pages for more details.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.5">3.5</a>) How do I set up a pg_group?</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Currently, there is no easy interface to set up user groups. You have to
|
|
|
|
|
explicitly insert/update the pg_group table. For example:
|
1998-02-27 23:01:58 +01:00
|
|
|
<PRE>
|
|
|
|
|
<CODE>
|
|
|
|
|
jolly=> insert into pg_group (groname, grosysid, grolist)
|
|
|
|
|
jolly=> values ('posthackers', '1234', '{5443, 8261}');
|
1997-07-13 22:00:14 +02:00
|
|
|
INSERT 548224
|
1998-02-27 23:01:58 +01:00
|
|
|
jolly=> grant insert on foo to group posthackers;
|
1997-07-13 22:00:14 +02:00
|
|
|
CHANGE
|
1998-02-27 23:01:58 +01:00
|
|
|
jolly=>
|
|
|
|
|
</CODE>
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
The fields in pg_group are:
|
|
|
|
|
<UL>
|
|
|
|
|
<LI> groname: the group name. This a char16 and should
|
|
|
|
|
be purely alphanumeric. Do not include underscores
|
|
|
|
|
or other punctuation.
|
|
|
|
|
<LI> grosysid: the group id. This is an int4.
|
|
|
|
|
This should be unique for each group.
|
|
|
|
|
<LI> grolist: the list of pg_user id's that belong in the group.
|
|
|
|
|
This is an int4[].
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.6">3.6</a>) What is the exact difference between binary
|
|
|
|
|
cursors and normal cursors?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
See the <I>declare</I> manual page for a description.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.7">3.7</a>) What is a R-tree index and what is it used for?
|
|
|
|
|
</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
The canonical paper that describes the original R-Tree design is:
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
You can also find this paper in Stonebraker's "Readings in Database
|
|
|
|
|
Systems"
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.8">3.8</a>) What is the maximum size for a tuple?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
Tuples do not cross 8k boundaries so a 5k tuple will require 8k of
|
|
|
|
|
storage.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.9">3.9</a>) I defined indices but my queries don't seem
|
|
|
|
|
to make use of them. Why?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
PostgreSQL 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). For column-specific optimization
|
|
|
|
|
statistics, use 'vacuum analyze'.
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
See the create_index manual page for information on what type classes
|
|
|
|
|
are available. It must match the field type.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Postgres does not warn the user when the improper index is created.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Indexes not used for ORDER BY operations.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.10">3.10</a>) How do I do regular expression searches?
|
|
|
|
|
case-insensitive regexp searching?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
See the <I>pgbuiltin</I> manual page. Search for <I>regular expression.</I>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.11">3.11</a>) I experienced a server crash during a
|
|
|
|
|
vacuum. How do I remove the lock file?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
See the <I>vacuum</I> manual page.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.12">3.12</a>) What is the difference between the various
|
|
|
|
|
character types?</H3>
|
|
|
|
|
<PRE>
|
1996-10-03 19:15:56 +02:00
|
|
|
Type Internal Name Notes
|
1996-08-19 00:14:33 +02:00
|
|
|
--------------------------------------------------
|
1996-10-03 19:15:56 +02:00
|
|
|
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
|
1998-02-27 23:01:58 +01:00
|
|
|
</PRE>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You need to use the internal name when doing internal operations.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
The last four types above are "varlena" types (i.e. the first four bytes
|
|
|
|
|
are the length, followed by the data). CHAR(#) allocates the maximum
|
|
|
|
|
number of bytes no matter how much data is stored in the field.
|
|
|
|
|
TEXT, VARCHAR(#), and BYTEA all have variable length on the disk, and
|
|
|
|
|
because of this, there is a small performance penalty for using them.
|
|
|
|
|
Specifically, the penalty is for access to any columns after the first
|
|
|
|
|
column of this type.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.13">3.13</a>) In a query, how do I detect if a field is NULL?
|
|
|
|
|
</H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You test the column with IS NULL and IS NOT NULL.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.14">3.14</a>) How do I see how the query optimizer is
|
|
|
|
|
evaluating my query?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
See the <I>explain</I> manual page.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.15">3.15</a>) How do I create a serial field?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Postgres does not allow the user to specifiy a user column as type
|
|
|
|
|
SERIAL. Instead, you can use each row's oid field as a unique value.
|
|
|
|
|
However, if you need to dump and reload the database, you need to use
|
|
|
|
|
pgdump's -o option or COPY's WITH OIDS option to preserver the oids.
|
|
|
|
|
<P>
|
|
|
|
|
We also have a SEQUENCE function that is similar to SERIAL. See the
|
1998-02-18 16:56:06 +01:00
|
|
|
create_sequence manual page.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
Another valid way of doing this is to create a function:
|
1998-02-27 23:01:58 +01:00
|
|
|
<PRE>
|
|
|
|
|
<CODE>
|
1997-07-13 22:00:14 +02:00
|
|
|
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';
|
1998-02-27 23:01:58 +01:00
|
|
|
</CODE>
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
then:
|
1998-02-27 23:01:58 +01:00
|
|
|
<PRE>
|
|
|
|
|
<CODE>
|
1997-07-13 22:00:14 +02:00
|
|
|
create table my_stuff (my_key int4, value text);
|
|
|
|
|
insert into my_stuff values (new_oid(), 'hello');
|
1998-02-27 23:01:58 +01:00
|
|
|
</CODE>
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
Yet another way is to use general trigger function autoinc()
|
|
|
|
|
from contrib/spi/autoinc.c.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.16">3.16</a>) What are the pg_psort.XXX files in my database
|
|
|
|
|
directory?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
They are temporary sort 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.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
If you have no transactions or sorts running at the time, it is safe to
|
|
|
|
|
delete the pg_psort.XXX files.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.17">3.17</a>) Why can't I connect to my database from
|
|
|
|
|
another machine?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
The default configuration allows only unix domain socket connections
|
|
|
|
|
from the local machine. To enable TCP/IP connections, use the
|
|
|
|
|
postmaster -i option You need to add a host entry to the file
|
|
|
|
|
pgsql/data/pg_hba. See the <I>hba_conf</I> manual page.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.18">3.18</a>) How do I find out what indexes or
|
|
|
|
|
operations are defined in the database?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
psql has a variety of backslash commands to show such information. Use
|
|
|
|
|
\? to see them.
|
|
|
|
|
<P>
|
|
|
|
|
Also try the file pgsql/src/tutorial/syscat.source. It illustrates many of
|
|
|
|
|
the 'select's needed to get information out of the database system
|
|
|
|
|
tables.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.19">3.19</a>) What is the time-warp feature and how does
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it relate to vacuum?</H3>
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<P>
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PostgreSQL no longer supports this feature. All support code has been
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removed. This was done to improve performance and reduce disk storage
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overhead.
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<P>
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<H3><a name="3.20">3.20</a>) What is an oid? What is a tid?</H3>
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<P>
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Oids are Postgres's answer to unique row ids or serial columns. Every
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row that is created in Postgres gets a unique oid. All oids generated
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by initdb are less than 16384 (from backend/access/transam.h). All
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post-initdb (user-created) oids are equal or greater that this. All
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these oids are unique not only within a table, or database, but unique
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within the entire postgres installation.
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<P>
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Postgres uses oids in its internal system tables to link rows in
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|
separate tables. These oids can be used to identify specific user rows
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and used in joins. It is recommended you use column type oid to store
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|
oid values. See the sql(l) manual page to see the other internal
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|
columns. You can create an index on the oid field for faster access.
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<P>
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1998-02-18 16:56:06 +01:00
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Tids are used to indentify specific physical rows with block and offset
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1998-02-27 23:01:58 +01:00
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values. Tids change after rows are modified or reloaded. They are used
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|
by index entries to point to physical rows. They can not be accessed
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|
through sql.
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<P>
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|
<H3><a name="3.21">3.21</a>) What is the meaning of some of the terms
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|
used in Postgres?</H3>
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<P>
|
1998-02-18 16:56:06 +01:00
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|
Some of the source code and older documentation use terms that have more
|
1998-02-27 23:01:58 +01:00
|
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|
common usage. Here are some:
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|
<UL>
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|
<LI> row, record, tuple
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<LI> attribute, field, column
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<LI> table, class
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<LI> retrieve, select
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<LI> replace, update
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<LI> append, insert
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<LI> oid, serial value
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<LI> portal, cursor
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<LI> range variable, table name, table alias
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</UL>
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<P>
|
1998-02-18 16:56:06 +01:00
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|
Please let me know if you think of any more.
|
1998-02-27 23:01:58 +01:00
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|
<P>
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|
<H3><a name="3.22">3.22</a>) What is Genetic Query Optimization?</H3>
|
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|
<P>
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|
|
The GEQO module in PostgreSQL is intended to solve the query
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|
|
optimization problem of joining many tables by means of a Genetic
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|
|
Algorithm (GA). It allows the handling of large join queries through
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|
non-exhaustive search.
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|
<P>
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|
For further information see README.GEQO <utesch@aut.tu-freiberg.de>.
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|
<P>
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|
<H3><a name="3.23">3.23</a>) How do you remove a column from a table?</H3>
|
1998-02-18 16:56:06 +01:00
|
|
|
We do not support ALTER TABLE DROP COLUMN, but do this:
|
1998-02-27 23:01:58 +01:00
|
|
|
<PRE>
|
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|
<CODE>
|
1997-09-14 04:09:10 +02:00
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|
SELECT ... -- select all columns but the one you want to remove
|
1997-09-04 07:34:47 +02:00
|
|
|
INTO TABLE new_table
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|
|
FROM old_table;
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|
|
DROP TABLE old_table;
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|
|
ALTER TABLE new_table RENAME TO old_table;
|
1998-02-27 23:01:58 +01:00
|
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|
</CODE>
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|
</PRE>
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|
<P>
|
|
|
|
|
<H3><a name="3.24">3.24</a>) How do SELECT only the first few rows of
|
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|
|
a query?</H3>
|
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|
<P>
|
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|
|
See the <I>fetch</I> manual page.
|
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|
<P>
|
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|
|
|
This only prevents all row results from being transfered to the client.
|
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|
|
|
The entire query must be evaluated, even if you only want just first few
|
|
|
|
|
rows.
|
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|
|
|
Consider a query that has and ORDER BY. There is no way to return any
|
|
|
|
|
rows until the entire query is evaluated and sorted.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.25">3.25</a>) Why can't I create a column named
|
|
|
|
|
"time"?<BR></H3>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
6.2.1 has added some new restricted keywords as we make PostgreSQL more
|
1998-02-27 23:01:58 +01:00
|
|
|
ANSI-92 compilant. The next release will have this restriction removed.
|
1998-02-18 16:56:06 +01:00
|
|
|
There is a patch on ftp.postgresql.org that will allow this feature now.
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
|
|
|
|
<H3><a name="3.26">3.26</a>)How much database disk space is required
|
|
|
|
|
to store data from a typical flat file?<BR></H3>
|
|
|
|
|
<P>
|
|
|
|
|
Consider a file with 300,000 lines with two integers on each line.
|
|
|
|
|
The flat file is 2.4MB. The size of the PostgreSQL database file
|
|
|
|
|
containing this data can be estimated:
|
|
|
|
|
<PRE>
|
1998-02-01 22:20:26 +01:00
|
|
|
40 bytes + each row header (approximate)
|
|
|
|
|
8 bytes + two int fields @ 4 bytes each
|
|
|
|
|
4 bytes + pointer on page to tuple
|
|
|
|
|
-------- =
|
|
|
|
|
52 bytes per row
|
|
|
|
|
|
|
|
|
|
The data page size in PostgreSQL is 8192(8k) bytes, so:
|
|
|
|
|
|
|
|
|
|
8192 bytes per page
|
|
|
|
|
------------------- = 157 rows per database page (rounded up)
|
|
|
|
|
52 bytes per row
|
|
|
|
|
|
|
|
|
|
300000 data rows
|
|
|
|
|
----------------- = 1911 database pages
|
|
|
|
|
157 rows per page
|
|
|
|
|
|
|
|
|
|
1911 database pages * 8192 bytes per page = 15,654,912 or 15.5MB
|
1998-02-27 23:01:58 +01:00
|
|
|
<P>
|
1998-02-01 22:20:26 +01:00
|
|
|
Indexes do not contain as much overhead, but do contain the data that
|
|
|
|
|
is being indexed, so they can be large also.
|
1998-02-27 23:01:58 +01:00
|
|
|
</PRE>
|
|
|
|
|
<P>
|
|
|
|
|
<HR>
|
|
|
|
|
<H2> Section 4: Extending PostgreSQL
|
|
|
|
|
</H2>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="4.1">4.1</a>) I wrote a user-defined function and when I run
|
|
|
|
|
it
|
|
|
|
|
in psql, it dumps core.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="4.2">4.2</a>) I get messages of the type
|
|
|
|
|
NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="4.3">4.3</a>) I've written some nifty new types and functions
|
|
|
|
|
for
|
|
|
|
|
PostgreSQL.</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Please share them with other PostgreSQL users. Send your extensions to
|
|
|
|
|
mailing list, and they will eventually end up in the contrib/
|
|
|
|
|
subdirectory.
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="4.4">4.4</a>) How do I write a C function to return a tuple?<
|
|
|
|
|
/H3>
|
|
|
|
|
<P>
|
|
|
|
|
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.
|
|
|
|
|
<P>
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
<H2> Section 5: Bugs
|
|
|
|
|
</H2>
|
|
|
|
|
<P>
|
|
|
|
|
<H3><a name="5.1">5.1</a>) How do I make a bug report?</H3>
|
|
|
|
|
<P>
|
|
|
|
|
Check the current FAQ at <a
|
|
|
|
|
href="http://postgreSQL.org">http://postgreSQL.org</a>
|
|
|
|
|
<P>
|
|
|
|
|
Also check out our ftp site <a
|
|
|
|
|
href="ftp://ftp.postgreSQL.org/pub">ftp://ftp.postgreSQL.org/pub</a> to
|
|
|
|
|
see if there is a more recent PostgreSQL version.
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
You can also fill out the "bug-template" file and send it to:
|
1998-02-27 23:01:58 +01:00
|
|
|
<UL>
|
|
|
|
|
<LI> <a href="mailto:bugs@postgreSQL.org">bugs@postgreSQL.org</a>
|
|
|
|
|
</UL>
|
|
|
|
|
<P>
|
1998-02-18 16:56:06 +01:00
|
|
|
This is the address of the developers mailing list.
|
1998-02-27 23:01:58 +01:00
|
|
|
</BODY>
|
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|
</HTML>
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