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Remove old doc files, now README.

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Bruce Momjian 2000-06-15 19:08:37 +00:00
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49
contrib/array/array_iterator.doc
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Array iterator functions, by Massimo Dal Zotto <dz@cs.unitn.it>
Copyright (C) 1999, Massimo Dal Zotto <dz@cs.unitn.it>
This software is distributed under the GNU General Public License
either version 2, or (at your option) any later version.
This loadable module defines a new class of functions which take
an array and a scalar value, iterate a scalar operator over the
elements of the array and the value, and compute a result as
the logical OR or AND of the iteration results.
For example array_int4eq returns true if some of the elements
of an array of int4 is equal to the given value:
array_int4eq({1,2,3}, 1) --> true
array_int4eq({1,2,3}, 4) --> false
If we have defined T array types and O scalar operators we can
define T x O x 2 array functions, each of them has a name like
"array_[all_]<basetype><operation>" and takes an array of type T
iterating the operator O over all the elements. Note however
that some of the possible combination are invalid, for example
the array_int4_like because there is no like operator for int4.
We can then define new operators based on these functions and use
them to write queries with qualification clauses based on the
values of some of the elements of an array.
For example to select rows having some or all element of an array
attribute equal to a given value or matching a regular expression:
create table t(id int4[], txt text[]);
-- select tuples with some id element equal to 123
select * from t where t.id *= 123;
-- select tuples with some txt element matching '[a-z]'
select * from t where t.txt *~ '[a-z]';
-- select tuples with all txt elements matching '^[A-Z]'
select * from t where t.txt[1:3] **~ '^[A-Z]';
The scheme is quite general, each operator which operates on a base type
can be iterated over the elements of an array. It seem to work well but
defining each new operators requires writing a different C function.
Furthermore in each function there are two hardcoded OIDs which reference
a base type and a procedure. Not very portable. Can anyone suggest a
better and more portable way to do it ?
See also array_iterator.sql for an example on how to use this module.

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contrib/datetime/datetime_functions.doc → contrib/datetime/README
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contrib/miscutil/misc_utils.doc
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Miscellaneous utility functions for PostgreSQL.
Copyright (C) 1999, Massimo Dal Zotto <dz@cs.unitn.it>
This software is distributed under the GNU General Public License
either version 2, or (at your option) any later version.
query_limit(n)
sets a limit on the maximum numbers of query returned from
a backend. It can be used to limit the result size retrieved
by the application for poor input data or to avoid accidental
table product while playying with sql.
backend_pid()
return the pid of our corresponding backend.
unlisten(relname)
unlisten from a relation or from all relations if the argument
is null, empty or '*'.
It is now obsoleted by the new unlisten command but still useful
if you want unlisten a name computed by the query.
Note that a listen/notify relname can be any ascii string, not
just valid relation names.
min(x,y)
max(x,y)
return the min or max bteween two integers.
assert_enable(bool)
enable/disable assert checkings in the backend, if it has been
compiled with USE_ASSERT_CHECKING.
assert_test(bool)
test the assert enable/disable code, if the backend has been
compiled with ASSERT_CHECKING_TEST.
--
Massimo Dal Zotto <dz@cs.unitn.it>

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contrib/string/string_io.doc
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String io module for postgresql.
Copyright (C) 1999, Massimo Dal Zotto <dz@cs.unitn.it>
This software is distributed under the GNU General Public License
either version 2, or (at your option) any later version.
These output functions can be used as substitution of the standard text
output functions to get the value of text fields printed in the format
used for C strings. This allows the output of queries or the exported
files to be processed more easily using standard unix filter programs
like perl or awk.
If you use the standard functions instead you could find a single tuple
splitted into many lines and the tabs embedded in the values could be
confused with those used as field delimters.
My function translates all non-printing characters into corresponding
esacape sequences as defined by the C syntax. All you need to reconstruct
the exact value in your application is a corresponding unescape function
like the string_input defined in the source code.
Massimo Dal Zotto <dz@cs.unitn.it>

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contrib/userlock/user_locks.doc
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User locks, by Massimo Dal Zotto <dz@cs.unitn.it>
Copyright (C) 1999, Massimo Dal Zotto <dz@cs.unitn.it>
This software is distributed under the GNU General Public License
either version 2, or (at your option) any later version.
This loadable module, together with my user-lock.patch applied to the
backend, provides support for user-level long-term cooperative locks.
For example one can write:
select some_fields, user_write_lock_oid(oid) from table where id='key';
Now if the returned user_write_lock_oid field is 1 you have acquired an
user lock on the oid of the selected tuple and can now do some long operation
on it, like let the data being edited by the user.
If it is 0 it means that the lock has been already acquired by some other
process and you should not use that item until the other has finished.
Note that in this case the query returns 0 immediately without waiting on
the lock. This is good if the lock is held for long time.
After you have finished your work on that item you can do:
update table set some_fields where id='key';
select user_write_unlock_oid(oid) from table where id='key';
You can also ignore the failure and go ahead but this could produce conflicts
or inconsistent data in your application. User locks require a cooperative
behavior between users. User locks don't interfere with the normal locks
used by postgres for transaction processing.
This could also be done by setting a flag in the record itself but in
this case you have the overhead of the updates to the records and there
could be some locks not released if the backend or the application crashes
before resetting the lock flag.
It could also be done with a begin/end block but in this case the entire
table would be locked by postgres and it is not acceptable to do this for
a long period because other transactions would block completely.
The generic user locks use two values, group and id, to identify a lock,
which correspond to ip_posid and ip_blkid of an ItemPointerData.
Group is a 16 bit value while id is a 32 bit integer which could also be
an oid. The oid user lock functions, which take only an oid as argument,
use a group equal to 0.
The meaning of group and id is defined by the application. The user
lock code just takes two numbers and tells you if the corresponding
entity has been succesfully locked. What this mean is up to you.
My succestion is that you use the group to identify an area of your
application and the id to identify an object in this area.
Or you can just lock the oid of the tuples which are by definition unique.
Note also that a process can acquire more than one lock on the same entity
and it must release the lock the corresponding number of times. This can
be done calling the unlock funtion until it returns 0.