Back again, getting very less time for blogging :)
“ERROR: could not create unique indexDETAIL: Table contains duplicated values."This error is thrown out by Postgres when it encounters duplicate rows in a primary key table by failing any of these command REINDEX or CREATE UNIQUE INDEX.
Why duplicate rows exists in a table ?
Not sure exactly :) nor any proved explainations out…
Two thing to my mind.
Firstly, it might be delayed index creation or if you have shared sequences in a database, sharing on two different Primary key Tables might be the cause while restoring the data into table (pg_restore).
Londiste, Asynchronous Master/Slave replication tool developed by Skytools. Its very simple and user-friendly created like Slony. Core logic behind Londiste or Slony is Remote Triggering. Whereas londiste follows events queuing model which is not their in Slony - I.
Overview on Skytools:
Skytools is a Python-based application, it comes with a bundle of three things PgQ,Londiste & Walmgr and it also requires the Python-Postgres driver ‘psycopg2’.
PGQ : Its queue mechanism built with pl/pgsql with phython framework on top of it.
Note: Recommended not to tamper pg_catalogs.
On forum, I saw an interesting posting and also the solution, however few things of that solution made me to test it. Scenario is, “How to resize the VARCHAR column on a large table with less time and what are best approach’s”. As known standard way is to, Create a NEW column with desired size, Copy OLD data to newly created column, Drop the OLD column and finally rename the NEW with OLD column name.
Before discussing on deadlocks, lets see type of locks and their acquiring methodolgy in PostgreSQL.
Types of Locks:
Table-Level Locks and Row-Level Locks
Table-Level Locks:
AcessShareLock : It acquired automatically by a SELECT statement on the table or tables it retrieves from. This mode blocks ALTER TABLE, DROP TABLE, and *VACUUM (AccessExclusiveLock) *on the same table RowShareLock :It acquired automatically by a SELECT…FOR UPDATE clause. It blocks concurrent ExclusiveLock and *AccessExclusiveLock *on the same table.
In our regular DBA monitoring, we will be using so many combination of pg_catalog queries to reteive information like <IDLE> in transaction , waiting queries, No. of connections, etc. Most of the DBA’s, create views to cut short big combination queries and keep handy for later use per requirement.
PostgreSQL, provides a startup file(.psqlrc) which executes before connecting to the database when using with psql utility. Using .psqlrc file you can place all your important queries with one word alias by ‘\set’ command and execute it in psql terminal instead of typing big queries.