Feb 02

PosgreSQL DBA commands for Beginners

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PostgreSQL is world best open source database. PostgrSQL is RDBMS database like Oracle . The main advantage of PostgreSQL is that it’s open source and free. Moreover, PostgreSQL provides comparable features like Oracle. Today, I came across an useful PostgreSQL Database Administration commands series. I would highly recommend following articles for the beginners to get hands on experience quickly in the PostgreSQL database administration.

Here are the links:
I hope these articles will help you to start your career in PostgreSQL database administration.
Jan 21

Find MySQL table level Insert/Update/Delete Statistics

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Many customers are asking for getting stats from their MySQL installation. It’s pretty easy to find stats per database from Com_ variables and graph them as counter to get the number of INSERT/UPDATE/DELETE on the database level. To get the DML stats from MySQL at table level there is only one option : mysqlbinlog . Here is the best post I found that can help you to answer your question.

Get the MySQL table stats now!
Jan 17

CREATE TABLE … PARTITION BY RANGE . Will it be possible in PosgreSQL?

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Oracle’s easy to create and manage partition table feature is the best selling point for them to attract wide range of applications to use partitioning features easily . Oracle supports partitioning since Oracle8i but there were limited features in the first release. In Oracle8i, they supported only RANGE and HASH partitions management.

On the other hand, PostgreSQL support partitioning but it’s cumbersome to create and manage partitioned tables. At least to start with, PostgreSQL should implement commands to make RANGE partition creation and management easy for the users. .
This is an example for creating range partitioned tables in Oracle …
CREATE TABLE users
( user_id    NUMBER NOT NULL,
registration_date  DATE   NOT NULL,
notes      VARCHAR2(500))
PARTITION BY RANGE (registration_date)
(PARTITION users_q1 VALUES LESS THAN (TO_DATE('01/04/2011', 'DD/MM/YYYY')) TABLESPACE users,
PARTITION users_q2 VALUES LESS THAN (TO_DATE('01/07/2011', 'DD/MM/YYYY')) TABLESPACE users,
PARTITION users_q3 VALUES LESS THAN (TO_DATE('01/09/2011', 'DD/MM/YYYY')) TABLESPACE users,
PARTITION users_q4 VALUES LESS THAN (TO_DATE('01/01/2012', 'DD/MM/YYYY')) TABLESPACE users);
When will I be able to CREATE range partition table and manage with ALTER TABLE commands in PostgreSQL?
Nov 22

Possibility of Graceful Switchover?

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I have been using PITR master-slave solution for long time for “failover” to slave server when there is a problem with the master server. It has proven a valuable solution for most of clients needs. The problem with “failover” solution is that we have to rebuild old-master as slave from completely new base backup from newly promoted master server. Oracle provides nice feature called “Graceful Switchover“. In this method, you can switch duty between master and slave servers and don’t have to rebuild old-master as slave from newly promoted master server. It could be very useful during server or data center move as we can shutdown old database and can have total control over xlogs to be processed before we start traffic on newly promoted master database.

I couldn’t find any graceful switchover document or blog for the PostgreSQL . Today, I spent some time on testing same theory as Oracle uses for the switchover. Oracle controls switchover using controlfile, Why can’t I use pg_control to do the same in totally controlled environment?
For PostgreSQL graceful switchover, I tested following scenario on very small test database server with pre configured setup of master and PITR slave database:
  • Step-1 : Shutdown current master database
  • Step-2 : Apply all wal logs including the one created during shutdown process to slave database server
  • Step-3: Promote slave as master in read/write mode using triggered failover file
  • Step-4: Before pointing production traffic to newly promoted master server, take backup of $PGDATA/global/pg_control and $PGDATA/global/pgstat.stat files. These two files differ between master and slave after failing over slave database into production mode.
  • Step-5: Setup old – master server for slave for newly promoted master sever and replace $PGDATA/global/pg_control and $PGDATA/global/pgstat.stat with the files backed up in Step-4
  • Step-6: Check log files on old-master to make sure that it’s recovering copied wal logs from newly promoted master server(old-slave server)
Yay! I could successfully switched over slave to master and vice versa !
At this stage, old-master(new slave) started playing wal logs coming from new-master(old-slave) server. After that, I failed over new slave server to make sure we can actually bring the database in production mode. It worked like a charm!! I ran database wide vacuum after failover and it ran fine without any error.
I have done limited testing as I have tested this with very tiny setup of “pagila” database on test server and I don’t recommend you to use on the “production database” servers as of now.
Please test this in your test or dev environment and let me know your results and concerns!!
Nov 09

PostgreSQL : Track functions to tune

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Starting from PostgreSQL 8.4, there is a valuable addition in PostgreSQL features list: Per function statistics. Prior to this feature , there wasn’t an easy way to find out most time consuming functions in the database.

For time spent on single call, it’s easy to find out by executing function manually but it was too cumbersome and in some cases impossible to find out total time spent by function for the given time period. Enabling full logging and aggregating duration for each call by reading large log files was the only way to get that statistic. Now, you can find this details by querying a single view pg_stat_user_functions ! Awesome!
To enable function tracking you need to enable “track_functions” postgresql.conf parameter. The default is none, which disables function statistics tracking. Specify pl to track only procedural-language functions, all to also track SQL and C language functions.

#track_functions = none # none, pl, all

Once you have track_functions enabled in your database, you can get details by querying pg_stat_user_functions view:

select * from pg_stat_user_functions;


It provides following details:

funcid
schemaname
funcname
calls
total_time
self_time

Self time is the amount of time spent in the function itself, total time includes the time spent in functions it called. Time values are in milliseconds.

Here is the easy solution to track and find candidate that requires tuning!!
Nov 08

What’s blocking your way?

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If you’ve ever gotten a page about database connections are blocked, or phone call or email from an annoyed user whose transaction just won’t go through, or from a developer who can’t understand why application sessions are blocking each other, you know how useful it can be to identify not just whose lock is doing the blocking, but what object is locked.

Omniti’s labs project Tasty Treats for PostgreSQL provides useful tools for proactive database monitoring . email_locked_queries is the new addition to this toolset . This tool can be handy for proactive lock monitoring in your database to find the blocked and blocking sessions and it sends out email notification if the there is a connection waiting for lock(s) for more than 10 minutes. It’s trivial to change the query if you want to be notified at different threshold.

Let’s test the query tool and see the results by creating locking scenario:

postgres=# create table testlock(foo text,bar text);
CREATE TABLE
postgres=# insert into testlock values (‘lock’,'me’);
INSERT 0 1 postgres=# insert into testlock values (‘find’,'me’);
INSERT 0 1
postgres=# select * from testlock;
foo | bar
——+—–
find | me
lock | me
(2 rows)

Session 1:
 

postgres=# begin;
BEGIN
postgres=# update testlock set foo='hang' where foo='lock';
UPDATE 1

And Session 2, try to update same row: 

postgres=# begin;
BEGIN
postgres=# update testlock set foo='escapeme' where foo='lock';

This statement will hang, blocked by the lock that Session 1 is holding on the row.

I ran the query tool and I got this in my email: 
-[ RECORD 1 ]
--------+-----------------------------------------------------
locked_relation      |
locked_mode          | ShareLock
blocked_pid          | 9468
blocked_user         | postgres
blocked_statement    | update testlock set foo='escapeme' where foo='lock';
blocked_client_addr  |
blocked_query_age    | 00:10:28.98475
blocking_pid         | 8056
blocking_user        | postgres
blocking_statement   | IDLE in transaction
blocking_client_addr |
blocking_query_age   | 00:10:24.403767
blocking_xact_age    | 00:10:58.529881

Let me know if you have suggestions to make it more better.


Oct 30

Lessons

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I found these lessons shared by someone! He learned from a 90 year old person … Good read!!

1. Life isn’t fair, but it’s still good.
2. When in doubt, just take the next small step.
3. Life is too short to waste time hating anyone.
4. Your job won’t take care of you when you are sick. Your friends and parents will. Stay in touch.
5. Pay off your credit cards every month.
6. You don’t have to win every argument. Agree to disagree.
7. Cry with someone. It’s more healing than crying alone.
8. Save for retirement starting with your first paycheck.
9. When it comes to chocolate, resistance is futile.
10. Make peace with your past so it won’t screw up the present.
11. Don’t compare your life to others. You have no idea what their journey is all about.
12. If a relationship has to be a secret, you shouldn’t be in it..
13. Take a deep breath. It calms the mind..
14. Get rid of anything that isn’t useful, beautiful or joyful.
15. Whatever doesn’t kill you really does make you stronger.
16. It’s never too late to have a happy childhood. But the second one is up to you and no one else.
17. When it comes to going after what you love in life, don’t take no for an answer.
18. Burn the candles, use the nice sheets, wear the fancy lingerie. Don’t save it for a special occasion. Today is special.
19. Over-prepare, then go with the flow.
20. Be eccentric now. Don’t wait for old age to wear purple.
21.. The most important sex organ is the brain.
22. No one is in charge of your happiness but you.
23. Frame every so-called disaster with these words ”In five years, will this matter?”
24. Always choose life.
25. Forgive everyone everything.
26. What other people think of you is none of your business.
27. Time heals almost everything. Give time, time.
28. However good or bad a situation is, it will change.
29. Don’t take yourself so seriously. No one else does.
30. Believe in miracles.

31. Don’t audit life. Show up and make the most of it now.

32. Growing old beats the alternative — dying young.

33. Your children get only one childhood.
34. All that truly matters in the end is that you loved.
35. Get outside every day. Miracles are waiting everywhere.
36. If we all threw our problems in a pile and saw everyone else’s, we’d grab ours back.
37. Envy is a waste of time. You already have all you need.
38. The best is yet to come.
39. No matter how you feel, get up, dress up and show up.
40. Yield.
41. Life isn’t tied with a bow, but it’s still a gift.

Oct 28

RAID10 vs RAID5

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If you are working in IT industry, you must have come across these terms RAID10 and RAID5.
Let’s learn about RAID…

RAID 10:

RAID 10 = Combining features of RAID 0 + RAID 1. It provides optimization for fault tolerance. RAID 0 helps to increase performance by striping volume data across multiple disk drives. RAID 1 provides disk mirroring which duplicates your data.

RAID 5:


In RAID5, 4th disk is used for parity bit.

Database: We choose RAID10 over RAID5 for better performance.