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MongoDB for Oracle DBA’s Part 10 : Switchover & Role Transition between Primary and Secondary

In MongoDB as like Oracle Dataguard switchover is possible to but in different way.

You can ask Primary to stepdown and let nodes elect a new primary in replicaset. This can be done using rs.stepDown() method.

Before stepping down primary, one must know the below

The procedure blocks all writes to primary while it runs […]

MongoDB for Oracle DBA’s Part 8 : Understanding Data Distribution between Shards

With previous post, we have configured the two shards with each having replicaset rs0 and rs1.

In this post we will insert some data and observe how the data distribution is happening between shards.

To do the data distributed,

firstly the database must have the sharding enabled secondly, the collection which data need to […]

Independent Australia Oracle Users Group OTN DAYS 2016 – Conferences

Hello All,

IAOUG is back again in Australia for its second year consecutive year OTN Days, with Arup/Tim Hall/Connor around, two conferences being planned, please checkout if you are around Sydney / Goldcoast / or in Australia.

http://www.iaoug.com/home.html

Sydney, October 31st 2016

At […]

Quick Quiz : Find the best way to find how much time a query has taken to execute

Find the best way to find how much time the query (sql_id) has ran in past or current

ASH stores whenever a session is active every second in v$active_session_history for past two hours, In rotation one sample of every 10 seconds will be visible to dba_hist_active_session_history.

From v$active_session_history

select to_char(sample_time,’DD-MON-YY HH24′) Time, sql_id,sql_plan_hash_value,sql_exec_id,round((count(*))/60/60, 2) […]

Cassandra for Oracle DBA’s Part 18 : Change of Replication Factor & Repair Nodes

As like in ASM, when ever a disk is added a rebalance operation takes place between the disks, similarly when the replication factor is changed at keyspace level in the cassandra, the rebalance operation should take place, I have changed the replication factor for Keyspace and you should start the repair of each node so […]

Cassandra for Oracle DBA’s Part 14: Tombstones – Undo type structures

Undo like pointers, tombstones

Cassandra uses a log-structured storage engine. Because of this, deletes do not remove the rows and columns immediately and in-place. Instead, Cassandra writes a special marker, called a tombstone, indicating that a row, column, or range of columns was deleted. These tombstones are kept for at least the period of time […]

Cassandra for Oracle DBA’s Part 15 : Partition Merging & Compacting

Partition Merging or Compact or merging ss tables

Cassandra does not do in-place writes or updates. Rather, it uses a log structured format. Writes are done to Memtables, which are periodically flushed to disk as SSTables. As a result of this approach, the number of SSTables grows over time.

Having multiple SSTables causes […]

Cassandra for Oracle DBA’s Part 16 : Shutting Down Best Practices

Shutdown Best Practice While Cassandra is crash-safe, you can make a cleanershutdown and save some time during startup thus:

– Make other nodes think this one is down.

– nodetool -h $(hostname) -p 8080 disablegossip

– Wait a few secs, cut off anyone from writing to this node.

– nodetool -h $(hostname) -p […]

Cassandra for Oracle DBA Part 17: Tracing Sessions

As like oracle 100046 , you can also trace the Cassandra Session and it provide you the following information , the highlighted blue parts are important to understand that data has been fetched from different nodes and how many undo it has to read and how many from cache and how many reads […]

Cassandra for Oracle DBA’s Part 17: Backup & Recovery

Backup in Cassandra maintain at node level , so any backup that taken in the one node does not contain other nodes data, so you must take backup of each node, cassandra maintains backups as snapshots means an entire sstables at disk level copied to a different folder with snapshot id as like below.

root@wash-i-16ca26c8-prod […]