+++ /dev/null
-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.
+++ /dev/null
-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>
+++ /dev/null
-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>
+++ /dev/null
-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.
OSDN Git Service
