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Update FAQ.

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Bruce Momjian
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doc/FAQ
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@ -83,25 +83,21 @@
other users? other users?
4.17) What is an OID? What is a TID? 4.17) What is an OID? What is a TID?
4.18) What is the meaning of some of the terms used in PostgreSQL? 4.18) What is the meaning of some of the terms used in PostgreSQL?
4.19) Why do I get the error "FATAL: palloc failure: memory 4.19) How do I tell what PostgreSQL version I am running?
exhausted?" 4.20) My large-object operations get invalid large obj descriptor.
4.20) How do I tell what PostgreSQL version I am running?
4.21) My large-object operations get invalid large obj descriptor.
Why? Why?
4.22) How do I create a column that will default to the current time? 4.21) How do I create a column that will default to the current time?
4.23) Why are my subqueries using IN so slow? 4.22) Why are my subqueries using IN so slow?
4.24) How do I perform an outer join? 4.23) How do I perform an outer join?
Extending PostgreSQL Extending PostgreSQL
5.1) I wrote a user-defined function. When I run it in psql, why does 5.1) I wrote a user-defined function. When I run it in psql, why does
it dump core? it dump core?
5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 5.2) How can I contribute some nifty new types and functions to
not in alloc set!" mean?
5.3) How can I contribute some nifty new types and functions to
PostgreSQL? PostgreSQL?
5.4) How do I write a C function to return a tuple? 5.3) How do I write a C function to return a tuple?
5.5) I have changed a source file. Why does the recompile not see the 5.4) I have changed a source file. Why does the recompile not see the
change? change?
_________________________________________________________________ _________________________________________________________________
@ -887,26 +883,11 @@ BYTEA bytea variable-length byte array (null-safe)
A list of general database terms can be found at: A list of general database terms can be found at:
http://www.comptechnews.com/~reaster/dbdesign.html http://www.comptechnews.com/~reaster/dbdesign.html
4.19) Why do I get the error "FATAL: palloc failure: memory exhausted?" 4.19) How do I tell what PostgreSQL version I am running?
It is possible you have run out of virtual memory on your system, or
your kernel has a low limit for certain resources. Try this before
starting the postmaster:
ulimit -d 65536
limit datasize 64m
Depending on your shell, only one of these may succeed, but it will
set your process data segment limit much higher and perhaps allow the
query to complete. This command applies to the current process, and
all subprocesses created after the command is run. If you are having a
problem with the SQL client because the backend is returning too much
data, try it before starting the client.
4.20) How do I tell what PostgreSQL version I am running?
From psql, type select version(); From psql, type select version();
4.21) My large-object operations get invalid large obj descriptor. Why? 4.20) My large-object operations get invalid large obj descriptor. Why?
You need to put BEGIN WORK and COMMIT around any use of a large object You need to put BEGIN WORK and COMMIT around any use of a large object
handle, that is, surrounding lo_open ... lo_close. handle, that is, surrounding lo_open ... lo_close.
@ -920,12 +901,12 @@ BYTEA bytea variable-length byte array (null-safe)
If you are using a client interface like ODBC you may need to set If you are using a client interface like ODBC you may need to set
auto-commit off. auto-commit off.
4.22) How do I create a column that will default to the current time? 4.21) How do I create a column that will default to the current time?
Use now(): Use now():
CREATE TABLE test (x int, modtime timestamp DEFAULT now() ); CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
4.23) Why are my subqueries using IN so slow? 4.22) Why are my subqueries using IN so slow?
Currently, we join subqueries to outer queries by sequentially Currently, we join subqueries to outer queries by sequentially
scanning the result of the subquery for each row of the outer query. A scanning the result of the subquery for each row of the outer query. A
@ -941,7 +922,7 @@ SELECT *
We hope to fix this limitation in a future release. We hope to fix this limitation in a future release.
4.24) How do I perform an outer join? 4.23) How do I perform an outer join?
PostgreSQL 7.1 and later supports outer joins using the SQL standard PostgreSQL 7.1 and later supports outer joins using the SQL standard
syntax. Here are two examples: syntax. Here are two examples:
@ -980,23 +961,17 @@ SELECT *
The problem could be a number of things. Try testing your user-defined The problem could be a number of things. Try testing your user-defined
function in a stand-alone test program first. function in a stand-alone test program first.
5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in 5.2) How can I contribute some nifty new types and functions to PostgreSQL?
alloc set!" mean?
You are pfree'ing something that was not palloc'ed. Beware of mixing
malloc/free and palloc/pfree.
5.3) How can I contribute some nifty new types and functions to PostgreSQL?
Send your extensions to the pgsql-hackers mailing list, and they will Send your extensions to the pgsql-hackers mailing list, and they will
eventually end up in the contrib/ subdirectory. eventually end up in the contrib/ subdirectory.
5.4) How do I write a C function to return a tuple? 5.3) How do I write a C function to return a tuple?
This requires wizardry so extreme that the authors have never tried This requires wizardry so extreme that the authors have never tried
it, though in principle it can be done. it, though in principle it can be done.
5.5) I have changed a source file. Why does the recompile not see the 5.4) I have changed a source file. Why does the recompile not see the
change? change?
The Makefiles do not have the proper dependencies for include files. The Makefiles do not have the proper dependencies for include files.

64
doc/src/FAQ/FAQ.html
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@ -127,17 +127,15 @@
<SMALL>TID</SMALL>?<BR> <SMALL>TID</SMALL>?<BR>
<A href="#4.18">4.18</A>) What is the meaning of some of the terms <A href="#4.18">4.18</A>) What is the meaning of some of the terms
used in PostgreSQL?<BR> used in PostgreSQL?<BR>
<A href="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc <A href="#4.19">4.19</A>) How do I tell what PostgreSQL version I
failure: memory exhausted?"</I><BR>
<A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I
am running? <BR> am running? <BR>
<A href="#4.21">4.21</A>) My large-object operations get <A href="#4.20">4.20</A>) My large-object operations get
<I>invalid large obj descriptor.</I> Why?<BR> <I>invalid large obj descriptor.</I> Why?<BR>
<A href="#4.22">4.22</A>) How do I create a column that will <A href="#4.21">4.21</A>) How do I create a column that will
default to the current time?<BR> default to the current time?<BR>
<A href="#4.23">4.23</A>) Why are my subqueries using <A href="#4.22">4.22</A>) Why are my subqueries using
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR> <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
<A href="#4.24">4.24</A>) How do I perform an outer join?<BR> <A href="#4.23">4.23</A>) How do I perform an outer join?<BR>
<CENTER> <CENTER>
@ -145,14 +143,11 @@
</CENTER> </CENTER>
<A href="#5.1">5.1</A>) I wrote a user-defined function. When I run <A href="#5.1">5.1</A>) I wrote a user-defined function. When I run
it in <I>psql,</I> why does it dump core?<BR> it in <I>psql,</I> why does it dump core?<BR>
<A href="#5.2">5.2</A>) What does the message <A href="#5.2">5.2</A>) How can I contribute some nifty new types
<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
mean?<BR>
<A href="#5.3">5.3</A>) How can I contribute some nifty new types
and functions to PostgreSQL?<BR> and functions to PostgreSQL?<BR>
<A href="#5.4">5.4</A>) How do I write a C function to return a <A href="#5.3">5.3</A>) How do I write a C function to return a
tuple?<BR> tuple?<BR>
<A href="#5.5">5.5</A>) I have changed a source file. Why does the <A href="#5.4">5.4</A>) I have changed a source file. Why does the
recompile not see the change?<BR> recompile not see the change?<BR>
<HR> <HR>
@ -1137,32 +1132,13 @@ BYTEA bytea variable-length byte array (null-safe)
<P>A list of general database terms can be found at: <A href= <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://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
<H4><A name="4.19">4.19</A>) Why do I get the error <I>"FATAL: <H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version
palloc failure: memory exhausted?"</I><BR>
</H4>
<P>It is possible you have run out of virtual memory on your
system, or your kernel has a low limit for certain resources. Try
this before starting the <I>postmaster:</I></P>
<PRE>
ulimit -d 65536
limit datasize 64m
</PRE>
Depending on your shell, only one of these may succeed, but it will
set your process data segment limit much higher and perhaps allow
the query to complete. This command applies to the current process,
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.
<H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version
I am running?<BR> I am running?<BR>
</H4> </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="4.21">4.21</A>) My large-object operations get <H4><A name="4.20">4.20</A>) My large-object operations get
<I>invalid large obj descriptor.</I> Why?<BR> <I>invalid large obj descriptor.</I> Why?<BR>
</H4> </H4>
@ -1179,7 +1155,7 @@ BYTEA bytea variable-length byte array (null-safe)
<P>If you are using a client interface like <SMALL>ODBC</SMALL> you <P>If you are using a client interface like <SMALL>ODBC</SMALL> you
may need to set <CODE>auto-commit off.</CODE></P> may need to set <CODE>auto-commit off.</CODE></P>
<H4><A name="4.22">4.22</A>) How do I create a column that will <H4><A name="4.21">4.21</A>) How do I create a column that will
default to the current time?<BR> default to the current time?<BR>
</H4> </H4>
@ -1189,7 +1165,7 @@ BYTEA bytea variable-length byte array (null-safe)
</CODE> </CODE>
</PRE> </PRE>
<H4><A name="4.23">4.23</A>) Why are my subqueries using <H4><A name="4.22">4.22</A>) Why are my subqueries using
<CODE><SMALL>IN</SMALL></CODE> so slow?<BR> <CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
</H4> </H4>
@ -1212,7 +1188,7 @@ BYTEA bytea variable-length byte array (null-safe)
</PRE> </PRE>
We hope to fix this limitation in a future release. We hope to fix this limitation in a future release.
<H4><A name="4.24">4.24</A>) How do I perform an outer join?<BR> <H4><A name="4.23">4.23</A>) How do I perform an outer join?<BR>
</H4> </H4>
<P>PostgreSQL 7.1 and later supports outer joins using the SQL <P>PostgreSQL 7.1 and later supports outer joins using the SQL
@ -1264,28 +1240,20 @@ BYTEA bytea variable-length byte array (null-safe)
<P>The problem could be a number of things. Try testing your <P>The problem could be a number of things. Try testing your
user-defined function in a stand-alone test program first.</P> user-defined function in a stand-alone test program first.</P>
<H4><A name="5.2">5.2</A>) What does the message <H4><A name="5.2">5.2</A>) How can I contribute some nifty new
<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
mean?</H4>
<P>You are <I>pfree'</I>ing something that was not
<I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and
<I>palloc/pfree.</I></P>
<H4><A name="5.3">5.3</A>) How can I contribute some nifty new
types and functions to PostgreSQL?</H4> types and functions to PostgreSQL?</H4>
<P>Send your extensions to the <I>pgsql-hackers</I> mailing list, <P>Send your extensions to the <I>pgsql-hackers</I> mailing list,
and they will eventually end up in the <I>contrib/</I> and they will eventually end up in the <I>contrib/</I>
subdirectory.</P> subdirectory.</P>
<H4><A name="5.4">5.4</A>) How do I write a C function to return a <H4><A name="5.3">5.3</A>) How do I write a C function to return a
tuple?</H4> tuple?</H4>
<P>This requires wizardry so extreme that the authors have never <P>This requires wizardry so extreme that the authors have never
tried it, though in principle it can be done.</P> tried it, though in principle it can be done.</P>
<H4><A name="5.5">5.5</A>) I have changed a source file. Why does <H4><A name="5.4">5.4</A>) I have changed a source file. Why does
the recompile not see the change?</H4> the recompile not see the change?</H4>
<P>The <I>Makefiles</I> do not have the proper dependencies for <P>The <I>Makefiles</I> do not have the proper dependencies for