diff options
author | Bruce Momjian <bruce@momjian.us> | 2002-10-14 02:50:28 +0000 |
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committer | Bruce Momjian <bruce@momjian.us> | 2002-10-14 02:50:28 +0000 |
commit | 0896707ef612d69263838551ee9af526235f50dd (patch) | |
tree | 3a3c1c4cf8987290dc23e0fe524faa691dcc47ae /doc/src | |
parent | ad4ce7aa5b7385a0481009d1b8d8774435b03b0d (diff) | |
download | postgresql-0896707ef612d69263838551ee9af526235f50dd.tar.gz postgresql-0896707ef612d69263838551ee9af526235f50dd.zip |
FAQ updates from Ian Barwick.
Diffstat (limited to 'doc/src')
-rw-r--r-- | doc/src/FAQ/FAQ.html | 189 |
1 files changed, 87 insertions, 102 deletions
diff --git a/doc/src/FAQ/FAQ.html b/doc/src/FAQ/FAQ.html index 7553a988db3..042a4984ee4 100644 --- a/doc/src/FAQ/FAQ.html +++ b/doc/src/FAQ/FAQ.html @@ -14,7 +14,7 @@ alink="#0000ff"> <H1>Frequently Asked Questions (FAQ) for PostgreSQL</H1> - <P>Last updated: Fri Oct 11 13:54:56 EDT 2002</P> + <P>Last updated: Sun Oct 13 22:49:56 EDT 2002</P> <P>Current maintainer: Bruce Momjian (<A href= "mailto:pgman@candle.pha.pa.us">pgman@candle.pha.pa.us</A>)<BR> @@ -22,15 +22,14 @@ <P>The most recent version of this document can be viewed at <A href= - "http://www.Postgresql.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P> + "http://www.PostgreSQL.org/docs/faq-english.html">http://www.PostgreSQL.org/docs/faq-english.html</A>.</P> <P>Platform-specific questions are answered at <A href= "http://www.PostgreSQL.org/users-lounge/docs/faq.html">http://www.PostgreSQL.org/users-lounge/docs/faq.html</A>.</P> <HR> <H2 align="center">General Questions</H2> - <A href="#1.1">1.1</A>) What is PostgreSQL? How is it - pronounced?<BR> + <A href="#1.1">1.1</A>) What is PostgreSQL? How is it pronounced?<BR> <A href="#1.2">1.2</A>) What is the copyright on PostgreSQL?<BR> <A href="#1.3">1.3</A>) What Unix platforms does PostgreSQL run on?<BR> @@ -161,7 +160,7 @@ <H2 align="center">General Questions</H2> - <H4><A name="1.1">1.1</A>) What is PostgreSQL?</H4> + <H4><A name="1.1">1.1</A>) What is PostgreSQL? How is it pronounced?</H4> <P>PostgreSQL is pronounced <I>Post-Gres-Q-L</I>.</P> @@ -172,12 +171,12 @@ extended subset of <SMALL>SQL</SMALL>. PostgreSQL is free and the complete source is available.</P> - <P>PostgreSQL development is performed by a team of Internet + <P>PostgreSQL development is performed by a team of developers who all subscribe to the PostgreSQL development mailing list. The current coordinator is Marc G. Fournier (<A href= "mailto:scrappy@PostgreSQL.org">scrappy@PostgreSQL.org</A>). (See - below on how to join). This team is now responsible for all - development of PostgreSQL.</P> + section <a href="#1.6">1.6</a> on how to join). This team is now + responsible for all development of PostgreSQL.</P> <P>The authors of PostgreSQL 1.01 were Andrew Yu and Jolly Chen. Many others have contributed to the porting, testing, debugging, @@ -239,10 +238,10 @@ <P><STRONG>Client</STRONG></P> <P>It is possible to compile the <I>libpq</I> C library, psql, and - other interfaces and binaries to run on MS Windows platforms. In - this case, the client is running on MS Windows, and communicates + other interfaces and client applications to run on MS Windows platforms. + In this case, the client is running on MS Windows, and communicates via TCP/IP to a server running on one of our supported Unix - platforms. A file <I>win31.mak</I> is included in the distribution + platforms. A file <I>win32.mak</I> is included in the distribution for making a Win32 <I>libpq</I> library and <I>psql</I>. PostgreSQL also communicates with <SMALL>ODBC</SMALL> clients.</P> @@ -250,10 +249,11 @@ <P>The database server can run on Windows NT and Win2k using Cygwin, the Cygnus Unix/NT porting library. See - <I>pgsql/doc/FAQ_MSWIN</I> in the distribution or the <A href= - "http://www.postgresql.org/docs/faq-mswin.html">MS Windows FAQ</A> - on our web site. We have no plan to do a native port to any - Microsoft platform.</P> + <I>pgsql/doc/FAQ_MSWIN</I> in the distribution or the MS Windows FAQ + at <A href="http://www.PostgreSQL.org/docs/faq-mswin.html">http://www.PostgreSQL.org/docs/faq-mswin.html</A>.</P> + + <p>A native port to some Microsoft platforms is currently being worked + upon.</p> <H4><A name="1.5">1.5</A>) Where can I get PostgreSQL?</H4> @@ -318,7 +318,7 @@ '#PostgreSQL' "$USER" irc.phoenix.net.</CODE></P> <P>A list of commercial support companies is available at <A href= - "http://www.postgresql.org/users-lounge/commercial-support.html">http://www.postgresql.org/users-lounge/commercial-support.html</A>.</P> + "http://www.PostgreSQL.org/users-lounge/commercial-support.html">http://www.PostgreSQL.org/users-lounge/commercial-support.html</A>.</P> <H4><A name="1.7">1.7</A>) What is the latest release?</H4> @@ -339,10 +339,10 @@ "http://www.commandprompt.com/ppbook/">http://www.commandprompt.com/ppbook/</A>. There is a list of PostgreSQL books available for purchase at <A href= - "http://www.postgresql.org/books/">http://www.postgresql.org/books/</A>. + "http://www.ca.PostgreSQL.org/books/">http://www.ca.PostgreSQL.org/books/</A>. There is also a collection of PostgreSQL technical articles at <A href= - "http://techdocs.postgresql.org/">http://techdocs.postgresql.org/</A>.</P> + "http://techdocs.PostgreSQL.org/">http://techdocs.PostgreSQL.org/</A>.</P> <P><I>psql</I> has some nice \d commands to show information about types, operators, functions, aggregates, etc.</P> @@ -402,10 +402,10 @@ <H4><A name="1.13">1.13</A>) How do I submit a bug report?</H4> - <P>Please visit the <A href= - "http://www.postgresql.org/bugs/bugs.php">PostgreSQL BugTool</A> - page, which gives guidelines and directions on how to submit a - bug.</P> + <P>Please visit the PostgreSQL BugTool page at <A href= + "http://www.PostgreSQL.org/bugs/bugs.php">http://www.PostgreSQL.org/bugs/bugs.php</A>, + which gives guidelines and directions on how to submit a + bug report.</P> <P>Also check out our ftp site <A href= "ftp://ftp.PostgreSQL.org/pub">ftp://ftp.PostgreSQL.org/pub</A> to @@ -460,14 +460,14 @@ <DT><B>Support</B></DT> - <DD>Our mailing list provides a large group of developers and - users to help resolve any problems encountered. While we can not + <DD>Our mailing lists provide contact with a large group of developers + and users to help resolve any problems encountered. While we cannot guarantee a fix, commercial <SMALL>DBMS</SMALL>s do not always supply a fix either. Direct access to developers, the user community, manuals, and the source code often make PostgreSQL support superior to other <SMALL>DBMS</SMALL>s. There is commercial per-incident support available for those who need it. - (See <A href="#1.6">support FAQ item</A>.)<BR> + (See <A href="#1.6">FAQ section 1.6</A>.)<BR> <BR> </DD> @@ -484,7 +484,7 @@ PostgreSQL?</H4> <P>PostgreSQL has had a first-class infrastructure since we started - six years ago. This is all thanks to Marc Fournier, who has created + in 1994. This is all thanks to Marc Fournier, who has created and managed this infrastructure over the years.</P> <P>Quality infrastructure is very important to an open-source @@ -494,9 +494,7 @@ <P>Of course, this infrastructure is not cheap. There are a variety of monthly and one-time expenses that are required to keep it going. If you or your company has money it can donate to help fund - this effort, please go to <A href= - "https://store.pgsql.com/shopping/index.php?id=1"> - https://store.pgsql.com/shopping/index.php?id=1</A> + this effort, please go to <A href="http://store.pgsql.com/shopping/">http://store.pgsql.com/shopping/</A> and make a donation.</P> <P>Although the web page mentions PostgreSQL, Inc, the @@ -538,28 +536,23 @@ <P>A nice introduction to Database-backed Web pages can be seen at: <A href="http://www.webreview.com">http://www.webreview.com</A></P> - <P>There is also one at <A href= - "http://www.phone.net/home/mwm/hotlist/">http://www.phone.net/home/mwm/hotlist/.</A></P> - <P>For Web integration, PHP is an excellent interface. It is at <A href="http://www.php.net">http://www.php.net</A>.</P> - <P>For complex cases, many use the Perl interface and CGI.pm.</P> + <P>For complex cases, many use the Perl interface and CGI.pm or mod_perl.</P> <H4><A name="2.3">2.3</A>) Does PostgreSQL have a graphical user interface? A report generator? An embedded query language interface?</H4> - <P>We have a nice graphical user interface called <I>pgaccess</I>, - which is shipped as part of the distribution. <I>pgaccess</I> also - has a report generator. The Web page is <A href= - "http://www.flex.ro/pgaccess">http://www.flex.ro/pgaccess</A></P> + <P>We have a nice graphical user interface called PgAccess, which is + shipped as part of the distribution. PgAccess also has a report + generator. The Web page is <A href="http://www.pgaccess.org/">http://www.pgaccess.org/</A>.</P> <P>We also include <I>ecpg</I>, which is an embedded SQL query language interface for C.</P> - <H4><A name="2.4">2.4</A>) What languages are available to - communicate with PostgreSQL?</H4> + <H4><A name="2.4">2.4</A>) What languages are able to communicate with PostgreSQL?</H4> <P>We have:</P> @@ -572,7 +565,7 @@ <LI>Java (jdbc)</LI> - <LI>Perl (perl5)</LI> + <LI>Perl (DBD::Pg)</LI> <LI>ODBC (odbc)</LI> @@ -582,12 +575,10 @@ <LI>C Easy API (libpgeasy)</LI> - <LI>Embedded <SMALL>HTML</SMALL> (<A href= - "http://www.php.net">PHP from http://www.php.net</A>)</LI> + <LI>PHP ('pg_' functions, Pear::DB)</LI> </UL> - <P>Additional interfaces are available at <a - href="http://www.postgresql.org/interfaces.html"> - http://www.postgresql.org/interfaces.html.</A> + <P>Additional interfaces are available at + <a href="http://www.PostgreSQL.org/interfaces.html">http://www.PostgreSQL.org/interfaces.html</A>. </P> <HR> @@ -774,7 +765,7 @@ the MaxBackendId constant in <I>include/storage/sinvaladt.h</I>.</P> - <H4><A name="3.9">3.9</A>) What are the <I>pg_sorttempNNN.NN</I> + <H4><A name="3.9">3.9</A>) What are the <I>pg_tempNNN.NN</I> files in my database directory?</H4> <P>They are temporary files generated by the query executor. For @@ -793,16 +784,16 @@ <P>The PostgreSQL team makes only small changes between minor releases, so upgrading from 7.2 to 7.2.1 does not require a dump and restore. - However, major releases often change the internal format of system - tables and data files. These changes are often complex, so we don't - maintain backward compatability for data files. A dump outputs data - in a generic format that can then be loaded in using the new internal - format. + However, major releases (e.g. from 7.2 to 7.3) often change the internal + format of system tables and data files. These changes are often complex, + so we don't maintain backward compatability for data files. A dump outputs + data in a generic format that can then be loaded in using the new internal + format.</P> - <P>In releases where the on-disk format does not change, the + <p>In releases where the on-disk format does not change, the <i>pg_upgrade</i> script can be used to upgrade without a dump/restore. The release notes mention whether <i>pg_upgrade</i> is available for the - release. + release.</p> <HR> @@ -821,7 +812,7 @@ <SMALL>SELECT</SMALL> ... <SMALL>LIMIT</SMALL>....</P> <P>The entire query may have to be evaluated, even if you only want - the first few rows. Consider a query that has an <SMALL>ORDER + the first few rows. Consider using a query that has an <SMALL>ORDER BY.</SMALL> If there is an index that matches the <SMALL>ORDER BY</SMALL>, PostgreSQL may be able to evaluate only the first few records requested, or the entire query may have to be evaluated @@ -840,8 +831,8 @@ <H4><A name="4.4">4.4</A>) How do you remove a column from a table?</H4> - <P>We do not support <SMALL>ALTER TABLE DROP COLUMN,</SMALL> but do - this:</P> + <P>Prior to version 7.3, <SMALL>ALTER TABLE DROP COLUMN</SMALL> is not supported. + You can do this instead:</P> <PRE> BEGIN; LOCK TABLE old_table; @@ -892,7 +883,7 @@ be estimated as 6.4 MB:</P> <PRE> 36 bytes: each row header (approximate) - 24 bytes: one int field and one text filed + 24 bytes: one int field and one text field + 4 bytes: pointer on page to tuple ---------------------------------------- 64 bytes per row @@ -957,7 +948,7 @@ SELECT col FROM tab ORDER BY col [ DESC ] - LIMIT 1 + LIMIT 1; </PRE> <P>When using wild-card operators such as <SMALL>LIKE</SMALL> or @@ -972,10 +963,10 @@ </UL> <LI>The search string can not start with a character class, e.g. [a-e].</LI> - <LI>Case-insensitive searches like <SMALL>ILIKE</SMALL> and - <I>~*</I> can not be used. Instead, use functional - indexes, which are described later in this FAQ.</LI> - <LI>The default <I>C</I> local must be used during + <LI>Case-insensitive searches such as <SMALL>ILIKE</SMALL> and + <I>~*</I> do not utilise indexes. Instead, use functional + indexes, which are described in section <a href="#4.12">4.12</a>.</LI> + <LI>The default <I>C</I> locale must be used during <i>initdb.</i></LI> </UL> <P> @@ -1032,13 +1023,13 @@ <PRE> SELECT * FROM tab - WHERE lower(col) = 'abc' + WHERE LOWER(col) = 'abc'; </PRE> This will not use an standard index. However, if you create a functional index, it will be used: <PRE> - CREATE INDEX tabindex on tab (lower(col)); + CREATE INDEX tabindex ON tab (LOWER(col)); </PRE> <H4><A name="4.13">4.13</A>) In a query, how do I detect if a field @@ -1053,8 +1044,8 @@ Type Internal Name Notes -------------------------------------------------- "char" char 1 character -CHAR(#) bpchar blank padded to the specified fixed length -VARCHAR(#) varchar size specifies maximum length, no padding +CHAR(n) bpchar blank padded to the specified fixed length +VARCHAR(n) varchar size specifies maximum length, no padding TEXT text no specific upper limit on length BYTEA bytea variable-length byte array (null-byte safe) </PRE> @@ -1069,8 +1060,8 @@ BYTEA bytea variable-length byte array (null-byte safe) stored out-of-line by <SMALL>TOAST</SMALL>, so the space on disk might also be less than expected.</P> - <P><SMALL>CHAR()</SMALL> is best when storing strings that are - usually the same length. <SMALL>VARCHAR()</SMALL> is best when + <P><SMALL>CHAR(n)</SMALL> is best when storing strings that are + usually the same length. <SMALL>VARCHAR(n)</SMALL> is best when storing variable-length strings but it limits how long a string can be. <SMALL>TEXT</SMALL> is for strings of unlimited length, maximum 1 gigabyte. <SMALL>BYTEA</SMALL> is for storing binary data, @@ -1111,11 +1102,11 @@ BYTEA bytea variable-length byte array (null-byte safe) <P>One approach is to retrieve the next <SMALL>SERIAL</SMALL> value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the - example table in <A href="#4.15.1">4.15.1</A>, that might look like - this in Perl:</P> + example table in <A href="#4.15.1">4.15.1</A>, an example in a + pseudo-language would look like this:</P> <PRE> - new_id = output of "SELECT nextval('person_id_seq')" - INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal'); + new_id = execute("SELECT nextval('person_id_seq')"); + execute("INSERT INTO person (id, name) VALUES (new_id, 'Blaise Pascal')"); </PRE> You would then also have the new value stored in @@ -1124,14 +1115,14 @@ BYTEA bytea variable-length byte array (null-byte safe) automatically created <SMALL>SEQUENCE</SMALL> object will be named <<I>table</I>>_<<I>serialcolumn</I>>_<I>seq</I>, where <I>table</I> and <I>serialcolumn</I> are the names of your table - and your <SMALL>SERIAL</SMALL> column, respectively. + and your <SMALL>SERIAL</SMALL> column, respectively. <P>Alternatively, you could retrieve the assigned <SMALL>SERIAL</SMALL> value with the <I>currval</I>() function <I>after</I> it was inserted by default, e.g.,</P> <PRE> - INSERT INTO person (name) VALUES ('Blaise Pascal'); - new_id = output of "SELECT currval('person_id_seq')"; + execute("INSERT INTO person (name) VALUES ('Blaise Pascal')"); + new_id = execute("SELECT currval('person_id_seq')"); </PRE> Finally, you could use the <A href="#4.16"><SMALL>OID</SMALL></A> @@ -1139,12 +1130,12 @@ BYTEA bytea variable-length byte array (null-byte safe) default value, though this is probably the least portable approach. In Perl, using DBI with Edmund Mergl's DBD::Pg module, the oid value is made available via <I>$sth->{pg_oid_status}</I> after - <I>$sth->execute()</I>. + <I>$sth->execute()</I>. <H4><A name="4.15.3">4.15.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a race condition with other users?</H4> - <P>No. Currval() returns the current value assigned by your + <P>No. <i>currval</i>() returns the current value assigned by your backend, not by all users.</P> <H4><A name="4.15.4">4.15.4</A>) Why aren't my sequence numbers @@ -1163,7 +1154,7 @@ BYTEA bytea variable-length byte array (null-byte safe) Every row that is created in PostgreSQL gets a unique <SMALL>OID</SMALL>. All <SMALL>OID</SMALL>s generated during <I>initdb</I> are less than 16384 (from - <I>backend/access/transam.h</I>). All user-created + <I>include/access/transam.h</I>). All user-created <SMALL>OID</SMALL>s are equal to or greater than this. By default, all these <SMALL>OID</SMALL>s are unique not only within a table or database, but unique within the entire PostgreSQL installation.</P> @@ -1186,12 +1177,11 @@ BYTEA bytea variable-length byte array (null-byte safe) COPY new TO '/tmp/pgtable'; DELETE FROM new; COPY new WITH OIDS FROM '/tmp/pgtable'; +</PRE> <!-- CREATE TABLE new_table (mycol int); INSERT INTO new_table (oid, mycol) SELECT oid, mycol FROM old_table; --> -</PRE> - <P>O<SMALL>ID</SMALL>s are stored as 4-byte integers, and will overflow at 4 billion. No one has reported this ever happening, and we plan to have the limit removed before anyone does.</P> @@ -1228,7 +1218,7 @@ BYTEA bytea variable-length byte array (null-byte safe) </UL> <P>A list of general database terms can be found at: <A href= - "http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P> + "http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html">http://hea-www.harvard.edu/MST/simul/software/docs/pkgs/pgsql/glossary/glossary.html</A></P> <H4><A name="4.18">4.18</A>) Why do I get the error <I>"ERROR: Memory exhausted in AllocSetAlloc()"</I>?</H4> @@ -1247,12 +1237,12 @@ BYTEA bytea variable-length byte array (null-byte safe) and all subprocesses created after the command is run. If you are having a problem with the <SMALL>SQL</SMALL> client because the backend is returning too much data, try it before starting the - client. + client. <H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version I am running?</H4> - <P>From <I>psql</I>, type <CODE>select version();</CODE></P> + <P>From <I>psql</I>, type <CODE>SELECT version();</CODE></P> <H4><A name="4.20">4.20</A>) Why does my large-object operations get <I>"invalid large obj descriptor"</I>?</H4> @@ -1288,22 +1278,18 @@ BYTEA bytea variable-length byte array (null-byte safe) returns many rows, <CODE><SMALL>IN</SMALL></CODE> is fastest. To speed up other queries, replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:</P> -<PRE> -<CODE>SELECT * +<PRE> SELECT * FROM tab - WHERE col IN (SELECT subcol FROM subtab) -</CODE> + WHERE col IN (SELECT subcol FROM subtab); </PRE> - to: -<PRE> -<CODE>SELECT * + to: +<PRE> SELECT * FROM tab - WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col) -</CODE> + WHERE EXISTS (SELECT subcol FROM subtab WHERE subcol = col); </PRE> For this to be fast, <CODE>subcol</CODE> should be an indexed column. - We hope to fix this limitation in a future release. + We hope to fix this limitation in a future release. <H4><A name="4.23">4.23</A>) How do I perform an outer join?</H4> @@ -1362,8 +1348,8 @@ BYTEA bytea variable-length byte array (null-byte safe) <P>You can return result sets from PL/pgSQL functions using <I>refcursors</I>. See <A href= - "http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html"> - http://developer.postgresql.org/docs/postgres/plpgsql-cursors.html,</A> + "http://www.PostgreSQL.org/idocs/index.php?plpgsql-cursors.html"> + http://www.PostgreSQL.org/idocs/index.php?plpgsql-cursors.html</A>, section 23.7.3.3.</P> <H4><A name="4.26">4.26</A>) Why can't I reliably create/drop @@ -1381,13 +1367,12 @@ BYTEA bytea variable-length byte array (null-byte safe) <P>There are several master/slave replication options available. These allow only the master to make database changes and the slave can only do database reads. The bottom of <a - href="http://gborg.postgresql.org/genpage?replication_research"> - http://gborg.postgresql.org/genpage?replication_research</a> lists + href="http://gborg.PostgreSQL.org/genpage?replication_research"> + http://gborg.PostgreSQL.org/genpage?replication_research</a> lists them. A multi-master replication solution is being worked on at <a - href="http://gborg.postgresql.org/project/pgreplication/projdisplay. - php">http://gborg.postgresql.org/project/pgreplication/projdisplay.php</a>.</P> + href="http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php">http://gborg.PostgreSQL.org/project/pgreplication/projdisplay.php</a>.</P> - <H4><A name="4.27">4.27</A>) What encryption options are available? + <H4><A name="4.28">4.28</A>) What encryption options are available? </H4> <UL> <LI><I>/contrib/pgcrypto</I> contains many encryption functions for @@ -1395,8 +1380,8 @@ BYTEA bytea variable-length byte array (null-byte safe) <LI>The only way to encrypt transmission from the client to the server is by using <I>hostssl</I> in <I>pg_hba.conf</I>.</LI> <LI>Database user passwords are automatically encrypted when stored - in version 7.3. In previous versions, you must enable - <I>password_encryption</I> in <I>postgresql.conf</I>.</LI> + in version 7.3. In previous versions, you must enable the option + <i>PASSWORD_ENCRYPTION</i> in <i>postgresql.conf</i>.</LI> <LI>The server can run using an encrypted file system.</LI> </UL> |