MemSQL Aggregation commands
some useful Aggregator commands. At Master Aggregator :- ——————— Please find the each command description at http://developers.memsql.com/docs/latest/ref/index.html#select mysql> select database(); +————+ | database() | +————+ | ycsb | +————+ 1 row in set (0.00 sec) mysql> show tables; +—————–+ |…
MongoDB ConfigDB differ issue – Recovery procedure
We have 3 config servers ( say config1, config2 & config3 ) in production and imagine we have config db differ issue (configdb mismatch) on the config1 & config3. Then we may have to follow the following procedure to recover…
How to add script in Linux start-up
To add the scripts in start-up, we can use any of the one following command. In the below scenario, say you wanted add mongod start/stop/restart script to Linux ( reboot/start-up) [root@12d4-dl585-03 init.d]# chkconfig –add mongod [root@12d4-dl585-03 init.d]# (OR) Add a…
MongoDB Custom script for Monitoring
Main PHP program ( mm.php ) :- [root@MyLabBox v8]# pwd /var/www/html/mongo/v8 [root@MyLabBox v8]# cat mm.php <?php ############################################################# ############################################################# header(‘Refresh:120’); include(“mm_data.php”); $data_cfg_file = “datanode.cfg”; $fd = fopen($data_cfg_file, ‘r’); $node=fgets($fd); $count=1; echo ” <tr>”; while ( $node != “”) { $out =…
MongoDB Shrink database for cleanup space released
When documents or collections are deleted, empty record blocks within data files arise. MongoDB attempts to reuse this space when possible, but it will never return this space to the file system. This behavior explains why fileSize never decreases despite…
Aggregation Framework Operators
Pipeline Operators :- NOTE The aggregation pipeline cannot operate on values of the following types: Symbol, MinKey, MaxKey,DBRef, Code, and CodeWScope. Pipeline operators appear in an array. Documents pass through the operators in a sequence. Name Description $project Reshapes a…
Administering Hadoop
Namenode directory structure :- —————————————— A newly formatted namenode creates the following directory structure: ${dfs.name.dir}/current/VERSION /edits /fsimage /fstime In my machine [root@myhostname current]# pwd /data/2/hadoop/tmp/dfs/name/current [root@myhostname current]# [root@myhostname current]# ll -lhtr total 16K -rw-r–r– 1 root root 110 Jul 22…
MongoDB High Availability Min configuration
If you have 1 Primary node, 1 Secondary node and 1 Arbiter, and you are using majority write, then you are requiring that the write be made on both the Primary and the Secondary. As soon as one of those…
MongoDB Aggregation Concepts
MongoDB provides the three approaches to aggregation, each with its own strengths and purposes for a given situation. This section describes these approaches and also describes behaviors and limitations specific to each approach. See also the chart that compares the…
MapReduce Job [hadoop]
Running our first MapReduce job We will use the WordCount example job which reads text files and counts how often words occur. The input is text files and the output is text files, each line of which contains a word…