Use scutil to set host name

scutil --set HostName "localhost"

scutil --get HostName 

Note: make sure "localhost" is set in your /etc/hosts file

HBase Snapshot Restrictions

HBase Snapshot has two restrictions :

1. If in any case, regions got merged (usually manually) after the snapshot got taken, the snapshot would be invalid. Splitting regions are fine to snapshot.

2. If you restore data to create a table from snapshot, the replication on another cluster of that new table won't guarantee the data is integral.

Setup local dev env

apply the pitch for os x

uname -a

copy the ip and put in /etc/hosts as an alias of localhost

setup dns servers in system preference -> network -> advanced -> dns



Run Service in debug mode

gradle :apps:[Service_Name]:run --debug-jvm -Pdebug

Gradle Notes

1. To show cmd options of task "test"

 gradle help --task :test

Find class in jar

in lib do:

grep package/or/classname *

result :

abc.jar

look thru classes within it:

less abc.jar


shift+g : to to bottum
shift+n : go backward
space: go forward page by page

HBase - advanced configuration on column family level

HBase - advanced configuration on column family level

Block Size
HFile block size.Default is 64k,If you want to good sequential scan performance,it;s better to have larger  block size.
        Setting is during table creation
        hbase(main):002:0> create 'mytable',   {NAME => 'colfam1', BLOCKSIZE => '65536'}
        Or with code
        On HColumnDescriptor there is a method : setBlocksize(int)

Block Cache
        You can block cache for specific column family in order to improve caching for other column families for example.

hbase(main):002:0> create 'mytable',
{NAME => 'colfam1', BLOCKCACHE => 'false’}

Aggresive caching

       You can choose column families to be in highter priority for caching.

       hbase(main):002:0> create 'mytable',
       {NAME => 'colfam1', IN_MEMORY => 'true'}

Bloom filters

       You enable bloom filters on the column family, like this:
       hbase(main):007:0> create 'mytable',
       {NAME => 'colfam1', BLOOMFILTER => 'ROWCOL'}

       A row-level bloom filter is enabled with ROW, and a qualifier-level bloom filter is enabled with ROWCOL

 TTL
       By defining Time To Live on some column family will delete the data after given amount  of time
       Example:
      hbase(main):002:0> create 'mytable', {NAME => 'colfam1', TTL => '18000'}

     Data in colfam1 that is older than 5 hours is deleted during the next major compaction.

Compression

    Compression defenition impacts HFiles and their data. This can save disk I/O and instead pay for higher CPU utilization.
    hbase(main):002:0> create 'mytable',
    {NAME => 'colfam1', COMPRESSION => 'SNAPPY'}

Cell versioning

    By default 3 versions of values are saved. Can be changed

    hbase(main):002:0> create 'mytable', {NAME => 'colfam1', VERSIONS => 5,
    MIN_VERSIONS => '1'}

Ops

1. disk info : df
io info : iostat
usage info: free
cpu info: top / htop (is pretty cool)
web io: iftop