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From William <yhxx...@163.com>
Subject Re:Can phoenix support HBase's TimeStamp?
Date Mon, 17 Oct 2016 02:24:29 GMT
Hi, Zhang Yang,
   I've implemented the multi-version feature in my own Phoenix branch. But this implementation
is supposed to be working in a very very limited scenario because there were so many things
to think about when designing it. Here are some primary problems that we must solve:
   * add new syntax to support select with timestamps, we should support select only one version
and multi version within a range and the number of versions too. For example:
     select * from test timestamps min, max;     // select all versions within the specified
time range
     select * from test timestamps ts;           // select a specified version
     select * from test version number;          // select specified number of versions
     select * from test version number timestamps min, max; // select specified number of
versions with a specified time range.
     Note that this is not standard SQL syntax, which is not recommended.
   * Timestamp is a Cell-level property in HBase, so we should support the same thing in Phoenix.
But how can we allow different timestamps for different columns in the same row? I modified
the ResultSet class and add some methods like 'public Map<Long, T> getAllT(index)' to
return all selected versions for a single column. One can call this method on different columns
for the same row to retrieve all the things he wants. Users must use PhoenixResultSet instead
of ResultSet, this is not recommended either.
   * How do we handle index updates/selects for multi-version? This is a messy problem, so
my implementation did not support multi-version for index tables.
   * do not support GROUP BY, ORDER BY or any nested query/upsert.
   * for batch commit, when you upsert the same row with different timestamps, Phoenix can
only commit the last timestamps you set. This is meaningless to do this. So I simply forbid
this scenario.
   * Phoenix encoded the KVs into one Cell at the RS side, but if we want to return multi-versions
for different columns, especially different timestamps for different columns, we must not
do the encoding. So we must modify the internals of Phoenix to support a brand new read path
to do this.


   Besides the huge efforts of implementing, IMHO, the primary problem is it's not easy to
implement this feature properly,  as each one may have a different requirement. You can implementing
this feature personally in your personal branch, but i don't know the best way to support
this in an official Phoenix release. What do you think of this? Any suggested design?


  Thanks.
  William.


At 2016-10-13 18:12:56, "Yang Zhang" <zhang.yang.dm@gmail.com> wrote:

Hello everyone


I saw that we can create a Phoenix table from an exist HBase table,(for detail)
My question is whether Phoenix can supprort the history version of my row? 


I am trying to  use Phoenix to store some info which have a lot of common columns,
such as a table "T1 ( c1, c2, c3, c4 )", many rows share the same c1,c2,c3,and the variable
column is c4,
Using HBase we can put  'T1',  'key1', ' f:c4', 'new value', timestamp,


And i can get previous version of this row,They all share the same c1,c2,c3 whice HBase only
store once.


Whether phoenix support to query history version of my row?


I got this jira link  , This is same as my question.


Hadoop is using for big data, and mlutiple version can help us reduce our date that unnecessary
I think phoenix should support this feature too.


If Phoenix shouldn't support multiple version, please tell me the reason.




Anyway thansks for your help, First 



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