This version of 0.90.x HBase can be started on data written by HBase 0.20.x or HBase 0.89.x. There is no need of a migration step. HBase 0.89.x and 0.90.x does write out the name of region directories differently -- it names them with a md5 hash of the region name rather than a jenkins hash -- so this means that once started, there is no going back to HBase 0.20.x.
Be sure to remove the
hbase-default.xml from your
conf directory on upgrade. A 0.20.x version of this file will
have sub-optimal configurations for 0.90.x HBase. The
hbase-default.xml file is now bundled into the HBase jar and
read from there. If you would like to review the content of this file, see it in the src
src/main/resources/hbase-default.xml or see HBase Default Configuration.
Finally, if upgrading from 0.20.x, check your
.META. schema in the
shell. In the past we would recommend that users run with a 16kb
hbase> scan '-ROOT-' in the
shell. This will output the current
.META. schema. Check
MEMSTORE_FLUSHSIZE size. Is it 16kb (16384)? If so, you will need
to change this (The 'normal'/default value is 64MB (67108864)). Run the script
bin/set_meta_memstore_size.rb. This will make the necessary
edit to your
.META. schema. Failure to run this change will make for
a slow cluster  .