Database Technologies

1. Transaction-level advisory locks: PostgreSQL provides a means for creating locks that have application-defined meanings. These are called advisory locks, because the system does not enforce their use — it is up to the application to use them correctly.  Till 9.0, postgreSQL had only Session level locks. Now, in PostgreSQL 9.1, we have transaction level advisory lock. Some examples are given below: BEGIN; -- grabbing txn locks multiple times SELECT pg_advisory_xact_lock(1), pg_advisory_xact_lock(1), pg_advisory_xact_lock_shared(2), pg_advisory_xact_lock_shared(2), pg_advisory_xact_lock(1, 1), pg_advisory_xact_lock(1, 1), pg_advisory_xact_lock_shared(2, 2), pg_advisory_xact_lock_shared(2, 2); SELECT locktype, classid, objid, objsubid, mode, granted FROM pg_locks WHERE locktype = 'advisory' ORDER BY classid, objid, objsubid; COMMIT; Advantage of Advisory lock are given below: 1. Advisory locks are faster 2. It avoid

There is always discussion of having UPSERT/MERGE in postgresql. Since, oracle and other RDBMS has this feature, therefore people ask about this feature in PostgeSQL. In previous version of PostgreSQL, we used to implement it using functions. Now in PostgreSQL 9.1, user can implement this feature using Writable CTE. PostgreSQL 9.1, now has Writable CTE using WTH. WITH provides a way to write auxiliary statements for use in a larger query. These statements, which are often referred to as Common Table Expressions or CTEs, can be thought of as defining temporary tables that exist just for one query. Each auxiliary statement in a WITH clause can be a SELECT, INSERT, UPDATE, or DELETE; and the WITH clause itself is attached to a primary statement that can also be a SELECT, INSERT, UPDATE, or DELETE. Lets see how we can use Writable CTE for UPSERT. Following are SQL Code which can be use in Oracle and PostgreSQL for creating sample data: For oracle: create table myTable (pid numb

1. SQL function format(text, …):  This function is similar to the C function sprintf; However only the following conversion specifications are recognized: %s interpolates the corresponding argument as a string %I escapes its argument as an SQL identifier %L escapes its argument as an SQL literal %% outputs a literal %. A conversion can reference an explicit parameter position by preceding the conversion specifier with n$, where n is the argument position Some Examples are given below: postgres=# select format('%1$s %3$s', 1, 2, 3); format -------- 1 3 (1 row) postgres=# select format('Hello %s', 'World'); format ------------- Hello World (1 row) postgres=# select format('Hello %s %1$s %s', 'World', 'Hello again'); format ------------------------------- Hello World World Hello again (1 row) 2. New string functions concat(), concat_ws(), left(), right(), and reverse() (i). concat() function:

1. pg_describe_object:  In PostgreSQL 9.1, pg_describe_object function has been added. Using this function, user can get human readable string for understanding the pg_depend content as given below: postgres=# select classid, objid, objsubid, pg_describe_object(classid, objid, objsubid) from pg_depend where classid <> 0 and pg_describe_object(classi classid | objid | objsubid | pg_describe_object ---------+-------+----------+------------------------------------------------ 1247 | 16426 | 0 | type test_money 1247 | 16425 | 0 | type test_money[] 1259 | 16424 | 0 | table test_money 1259 | 16429 | 0 | index test_money_idx 2606 | 16431 | 0 | constraint uniq_constraint on table test_money 2. quote_all_identifiers (boolean) parameter:  With this parameter, User can force quoating of all identifiers in EXMPLAIN and in system catalog functions like pg_get_viewdef(). Example is given below: postgr

PostgreSQL 9.1 has come with new options and Improvement for Client Application. So, I thought to blog about those improvements.   Deprecated createlang/droplang: In PostgreSQL 9.1, createlang/dronlang is now deprecated commands. Since in PostgreSQL 9.1, for creating additional language, user has to use CREATE EXTENSION SYNTAX , there these binaries now issue command given below: CREATE EXTENSION plperl; CREATE EXTENSION plpyhthon; Added Features in psql: In PostgreSQL 9.1, following are the important improvement done in psql command:   1. Know about connection. Now psql has meta command \conninfo which gives detal about current connections. So, if you are connected to PostgreSQL database, then you can use command "\conninfo" to get detail about your connections, some example is given below: postgres=# \conninfo You are connected to database "postgres" as user "postgres" via socket in "/tmp" at port "5432". postgres=# \conni

Since, PostgreSQL 9.1 has already been released and there are lot of new features added in it, so, I thought to blog about each features. Today, I am discussing about Synchronous and Asynchronous Replication supported in PostgreSQL 9.1. For Asynchronous Replication, user can use following method: 1. Change Following Parameters in postgresql.conf file of Primary Database: archive_command = cp -i %p /Users/postgres/archive/%f archive_mode = on max_wal_senders = 3 # Maximum 'wal_senders', processes responsible for managing a connection with a standby server wal_keep_segments = # How many WAL segments (=files) should be kept on the primary, whatever may happen (you won't have to copy them manually on the standby if the standby gets too far behind) wal_level = hot_standby 2. Make Following changes in pg_hba.conf host replication postgres [Ipv4 address of Standby Server]/32 trust host replication postgres [Ipv4 address of Master Server]/32 tr

Today, I thought to share my Training slides on FTS (Full Text Search) in PostgreSQL 9.0. I have used this presentation on giving training. Enjoy :). Full Text Search Training