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From Ashutosh Chauhan <hashut...@apache.org>
Subject Re: One Schema Per Partition? (Multiple schemas per table?)
Date Thu, 25 Aug 2011 01:14:58 GMT
Hey Tim,

Hive does support different schema's for different partitions. If your data
comes out garbled, that seems to be a bug then. In your case, is the
following sequence of steps resemble what you did:

a) create table tbl (id: int, name: string, level: int) partitioned by date;
b) -- add partitions
c) alter table tbl replace columns (id: int, level: int, name_id: int)
d) -- add more partitions.

If you do select * from tbl, then this should work. You need not to rewrite
any of your data. Can you provide more info about what output you were
expecting and what you got. Are there any error logs?

Ashutosh


On Mon, Aug 22, 2011 at 14:34, Time Less <timelessness@gmail.com> wrote:

> I found a set of slides from Facebook online about Hive that claims you can
> have a schema per partition in the table, this is exciting to us, because we
> have a table like so:
>
> id     int
> name   string
> level  int
> date   string
>
> And it's broken up into partitions by date. However, on a particular date
> last year, the table dramatically changed its schema to:
>
> id       int
> level    int
> date     string
> name_id  int
>
> So now if I do "select * from table" in hive, the data is completely
> garbled for whichever portion of data doesn't fit the Hive schema. We are
> considering re-writing the datafiles so they're the same before/after that
> date, but if Hive supports having two entirely different schemas depending
> on the partition, that'd be really convenient, since these datafiles are
> hundreds of gigabytes in size (and we do sort of like the idea of knowing
> how the datafile looked back then...).
>
> This page:
> https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-AlterTable%2FPartitionStatementsdoesn't
seem to have an appropriate example, so I'm left wondering.
>
> Has anyone done anything like this?
>
> --
> Tim Ellis
> Data Architect, Riot Games
>
>

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