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Update FAQ.
This commit is contained in:
Bruce Momjian
parent
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doc/FAQ
57
doc/FAQ
@ -83,25 +83,21 @@
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other users?
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4.17) What is an OID? What is a TID?
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4.18) What is the meaning of some of the terms used in PostgreSQL?
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4.19) Why do I get the error "FATAL: palloc failure: memory
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exhausted?"
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4.20) How do I tell what PostgreSQL version I am running?
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4.21) My large-object operations get invalid large obj descriptor.
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4.19) How do I tell what PostgreSQL version I am running?
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4.20) My large-object operations get invalid large obj descriptor.
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Why?
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4.22) How do I create a column that will default to the current time?
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4.23) Why are my subqueries using IN so slow?
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4.24) How do I perform an outer join?
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4.21) How do I create a column that will default to the current time?
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4.22) Why are my subqueries using IN so slow?
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4.23) How do I perform an outer join?
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Extending PostgreSQL
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5.1) I wrote a user-defined function. When I run it in psql, why does
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it dump core?
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0
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not in alloc set!" mean?
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5.3) How can I contribute some nifty new types and functions to
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5.2) How can I contribute some nifty new types and functions to
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PostgreSQL?
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5.4) How do I write a C function to return a tuple?
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5.5) I have changed a source file. Why does the recompile not see the
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5.3) How do I write a C function to return a tuple?
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5.4) I have changed a source file. Why does the recompile not see the
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change?
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_________________________________________________________________
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@ -887,26 +883,11 @@ BYTEA bytea variable-length byte array (null-safe)
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A list of general database terms can be found at:
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http://www.comptechnews.com/~reaster/dbdesign.html
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4.19) Why do I get the error "FATAL: palloc failure: memory exhausted?"
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It is possible you have run out of virtual memory on your system, or
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your kernel has a low limit for certain resources. Try this before
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starting the postmaster:
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ulimit -d 65536
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limit datasize 64m
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Depending on your shell, only one of these may succeed, but it will
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set your process data segment limit much higher and perhaps allow the
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query to complete. This command applies to the current process, and
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all subprocesses created after the command is run. If you are having a
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problem with the SQL client because the backend is returning too much
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data, try it before starting the client.
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4.20) How do I tell what PostgreSQL version I am running?
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4.19) How do I tell what PostgreSQL version I am running?
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From psql, type select version();
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4.21) My large-object operations get invalid large obj descriptor. Why?
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4.20) My large-object operations get invalid large obj descriptor. Why?
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You need to put BEGIN WORK and COMMIT around any use of a large object
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handle, that is, surrounding lo_open ... lo_close.
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@ -920,12 +901,12 @@ BYTEA bytea variable-length byte array (null-safe)
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If you are using a client interface like ODBC you may need to set
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auto-commit off.
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4.22) How do I create a column that will default to the current time?
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4.21) How do I create a column that will default to the current time?
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Use now():
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CREATE TABLE test (x int, modtime timestamp DEFAULT now() );
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4.23) Why are my subqueries using IN so slow?
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4.22) Why are my subqueries using IN so slow?
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Currently, we join subqueries to outer queries by sequentially
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scanning the result of the subquery for each row of the outer query. A
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@ -941,7 +922,7 @@ SELECT *
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We hope to fix this limitation in a future release.
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4.24) How do I perform an outer join?
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4.23) How do I perform an outer join?
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PostgreSQL 7.1 and later supports outer joins using the SQL standard
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syntax. Here are two examples:
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@ -980,23 +961,17 @@ SELECT *
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The problem could be a number of things. Try testing your user-defined
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function in a stand-alone test program first.
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
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alloc set!" mean?
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You are pfree'ing something that was not palloc'ed. Beware of mixing
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malloc/free and palloc/pfree.
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5.3) How can I contribute some nifty new types and functions to PostgreSQL?
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5.2) How can I contribute some nifty new types and functions to PostgreSQL?
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Send your extensions to the pgsql-hackers mailing list, and they will
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eventually end up in the contrib/ subdirectory.
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5.4) How do I write a C function to return a tuple?
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5.3) How do I write a C function to return a tuple?
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This requires wizardry so extreme that the authors have never tried
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it, though in principle it can be done.
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5.5) I have changed a source file. Why does the recompile not see the
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5.4) I have changed a source file. Why does the recompile not see the
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change?
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The Makefiles do not have the proper dependencies for include files.
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@ -127,17 +127,15 @@
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<SMALL>TID</SMALL>?<BR>
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<A href="#4.18">4.18</A>) What is the meaning of some of the terms
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used in PostgreSQL?<BR>
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<A href="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
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failure: memory exhausted?"</I><BR>
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<A href="#4.20">4.20</A>) How do I tell what PostgreSQL version I
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<A href="#4.19">4.19</A>) How do I tell what PostgreSQL version I
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am running? <BR>
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<A href="#4.21">4.21</A>) My large-object operations get
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<A href="#4.20">4.20</A>) My large-object operations get
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<I>invalid large obj descriptor.</I> Why?<BR>
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<A href="#4.22">4.22</A>) How do I create a column that will
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<A href="#4.21">4.21</A>) How do I create a column that will
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default to the current time?<BR>
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<A href="#4.23">4.23</A>) Why are my subqueries using
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<A href="#4.22">4.22</A>) Why are my subqueries using
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<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
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<A href="#4.24">4.24</A>) How do I perform an outer join?<BR>
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<A href="#4.23">4.23</A>) How do I perform an outer join?<BR>
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<CENTER>
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@ -145,14 +143,11 @@
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</CENTER>
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<A href="#5.1">5.1</A>) I wrote a user-defined function. When I run
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it in <I>psql,</I> why does it dump core?<BR>
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<A href="#5.2">5.2</A>) What does the message
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<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
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mean?<BR>
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<A href="#5.3">5.3</A>) How can I contribute some nifty new types
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<A href="#5.2">5.2</A>) How can I contribute some nifty new types
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and functions to PostgreSQL?<BR>
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<A href="#5.4">5.4</A>) How do I write a C function to return a
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<A href="#5.3">5.3</A>) How do I write a C function to return a
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tuple?<BR>
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<A href="#5.5">5.5</A>) I have changed a source file. Why does the
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<A href="#5.4">5.4</A>) I have changed a source file. Why does the
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recompile not see the change?<BR>
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<HR>
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@ -1137,32 +1132,13 @@ BYTEA bytea variable-length byte array (null-safe)
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<P>A list of general database terms can be found at: <A href=
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"http://www.comptechnews.com/~reaster/dbdesign.html">http://www.comptechnews.com/~reaster/dbdesign.html</A></P>
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<H4><A name="4.19">4.19</A>) Why do I get the error <I>"FATAL:
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palloc failure: memory exhausted?"</I><BR>
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</H4>
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<P>It is possible you have run out of virtual memory on your
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system, or your kernel has a low limit for certain resources. Try
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this before starting the <I>postmaster:</I></P>
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<PRE>
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ulimit -d 65536
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limit datasize 64m
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</PRE>
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Depending on your shell, only one of these may succeed, but it will
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set your process data segment limit much higher and perhaps allow
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the query to complete. This command applies to the current process,
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and all subprocesses created after the command is run. If you are
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having a problem with the <SMALL>SQL</SMALL> client because the
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backend is returning too much data, try it before starting the
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client.
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<H4><A name="4.20">4.20</A>) How do I tell what PostgreSQL version
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<H4><A name="4.19">4.19</A>) How do I tell what PostgreSQL version
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I am running?<BR>
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</H4>
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<P>From <I>psql,</I> type <CODE>select version();</CODE></P>
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<H4><A name="4.21">4.21</A>) My large-object operations get
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<H4><A name="4.20">4.20</A>) My large-object operations get
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<I>invalid large obj descriptor.</I> Why?<BR>
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</H4>
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@ -1179,7 +1155,7 @@ BYTEA bytea variable-length byte array (null-safe)
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<P>If you are using a client interface like <SMALL>ODBC</SMALL> you
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may need to set <CODE>auto-commit off.</CODE></P>
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<H4><A name="4.22">4.22</A>) How do I create a column that will
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<H4><A name="4.21">4.21</A>) How do I create a column that will
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default to the current time?<BR>
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</H4>
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@ -1189,7 +1165,7 @@ BYTEA bytea variable-length byte array (null-safe)
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</CODE>
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</PRE>
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<H4><A name="4.23">4.23</A>) Why are my subqueries using
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<H4><A name="4.22">4.22</A>) Why are my subqueries using
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<CODE><SMALL>IN</SMALL></CODE> so slow?<BR>
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</H4>
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@ -1212,7 +1188,7 @@ BYTEA bytea variable-length byte array (null-safe)
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</PRE>
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We hope to fix this limitation in a future release.
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<H4><A name="4.24">4.24</A>) How do I perform an outer join?<BR>
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<H4><A name="4.23">4.23</A>) How do I perform an outer join?<BR>
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</H4>
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<P>PostgreSQL 7.1 and later supports outer joins using the SQL
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@ -1264,28 +1240,20 @@ BYTEA bytea variable-length byte array (null-safe)
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<P>The problem could be a number of things. Try testing your
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user-defined function in a stand-alone test program first.</P>
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<H4><A name="5.2">5.2</A>) What does the message
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<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I>
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mean?</H4>
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<P>You are <I>pfree'</I>ing something that was not
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<I>palloc'</I>ed. Beware of mixing <I>malloc/free</I> and
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<I>palloc/pfree.</I></P>
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<H4><A name="5.3">5.3</A>) How can I contribute some nifty new
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<H4><A name="5.2">5.2</A>) How can I contribute some nifty new
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types and functions to PostgreSQL?</H4>
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<P>Send your extensions to the <I>pgsql-hackers</I> mailing list,
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and they will eventually end up in the <I>contrib/</I>
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subdirectory.</P>
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<H4><A name="5.4">5.4</A>) How do I write a C function to return a
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<H4><A name="5.3">5.3</A>) How do I write a C function to return a
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tuple?</H4>
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<P>This requires wizardry so extreme that the authors have never
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tried it, though in principle it can be done.</P>
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<H4><A name="5.5">5.5</A>) I have changed a source file. Why does
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<H4><A name="5.4">5.4</A>) I have changed a source file. Why does
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the recompile not see the change?</H4>
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<P>The <I>Makefiles</I> do not have the proper dependencies for
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