Last updated: Sat Apr 23 14:59:01 EDT 2005

4.12) What is an OID? What is a TID?

4.15) Why does my large-object operations get "invalid large obj

descriptor"?

4.16) How do I create a column that will default to the current time?

4.17) How do I perform an outer join?

4.18) How do I perform queries using multiple databases?

4.19) How do I return multiple rows or columns from a function?

4.20) Why do I get "relation with OID ##### does not exist" errors

4.21) What encryption options are available?

Extending PostgreSQL

5.1) I wrote a user-defined function. When I run it in psql, why does

it dump core?

5.2) How can I contribute some nifty new types and functions to

PostgreSQL?

5.3) How do I write a C function to return a tuple?

5.4) I have changed a source file. Why does the recompile not see the

change?

scan, use SET enable_seqscan TO 'off' and run tests to see if an index

scan is indeed faster.

You test the column with IS NULL and IS NOT NULL.

in your WHERE clause. Things that are true will sort higher than

space used is slightly greater than the declared size. However, these

data types are also subject to compression or being stored out-of-line

by TOAST, so the space on disk might also be less than expected.

<table>_<serialcolumn>_seq, where table and serialcolumn are the names

of your table and your SERIAL column, respectively.

4.12) What is an OID? What is a TID?

TIDs are used to identify specific physical rows with block and offset

values. TIDs change after rows are modified or reloaded. They are used

by index entries to point to physical rows.

4.15) Why does my large-object operations get "invalid large obj descriptor"?

You need to put BEGIN WORK and COMMIT around any use of a large object

handle, that is, surrounding lo_open ... lo_close.

Currently PostgreSQL enforces the rule by closing large object handles

at transaction commit. So the first attempt to do anything with the

handle will draw invalid large obj descriptor. So code that used to

work (at least most of the time) will now generate that error message

if you fail to use a transaction.

If you are using a client interface like ODBC you may need to set

auto-commit off.

4.16) How do I create a column that will default to the current time?

4.17) How do I perform an outer join?

4.18) How do I perform queries using multiple databases?

4.19) How do I return multiple rows or columns from a function?

4.20) Why do I get "relation with OID ##### does not exist" errors when

4.21) What encryption options are available?

* The server can run using an encrypted file system.

_________________________________________________________________

Extending PostgreSQL

5.1) I wrote a user-defined function. When I run it in psql, why does it dump

core?

The problem could be a number of things. Try testing your user-defined

function in a stand-alone test program first.

5.2) How can I contribute some nifty new types and functions to PostgreSQL?

Send your extensions to the pgsql-hackers mailing list, and they will

eventually end up in the contrib/ subdirectory.

5.3) How do I write a C function to return a tuple?

In versions of PostgreSQL beginning with 7.3, table-returning

functions are fully supported in C, PL/PgSQL, and SQL. See the

Programmer's Guide for more information. An example of a

table-returning function defined in C can be found in

contrib/tablefunc.

5.4) I have changed a source file. Why does the recompile not see the change?

The Makefiles do not have the proper dependencies for include files.

You have to do a make clean and then another make. If you are using

GCC you can use the --enable-depend option of configure to have the

compiler compute the dependencies automatically.