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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (PHOENIX-4550) Declare maximum columns to ensure storage is dense when table has many views
Date Sun, 11 Feb 2018 17:35:00 GMT

     [ https://issues.apache.org/jira/browse/PHOENIX-4550?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

James Taylor updated PHOENIX-4550:
----------------------------------
    Description: 
By declaring the max number of columns on a base table, we can optimize the storage for SINGLE_CELL_ARRAY_WITH_OFFSETS
by not storing null values for the columns preceding the initial column of a view. This will
make a huge difference in storage when you have a base table with many views. For example:

{code}
-- Declare that the base table will have no more than 10 columns
CREATE IMMUTABLE TABLE base (k1 VARCHAR, prefix CHAR(3) v1 DATE,
    CONSTRAINT pk PRIMARY KEY (k1, prefix))
    MULTI_TENANT = true,
    MAX_COLUMNS = 10;
CREATE VIEW v1(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR)
    AS SELECT * FROM base WHERE prefix = 'A00';
CREATE VIEW v2(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR);
    AS SELECT * FROM base WHERE prefix = 'A10';
...
{code}

As the number of views grow, the difference between the base table column encoding (column
#1) and the starting column number of the view (since the starting offset is determined by
an incrementing value on the base table) will increase. This bloats the storage as we need
to store null values for column encodings between the base table column and the starting column
of the view.

Instead, we'll pass through the MAX_COLUMNS value for queries and anything column encoding
less than this we know it'll be at the start. Anything greater and we'll start the search
from <column encoding> - <minimum view column encoding>.

The downside of this approach is if you run out of columns in the base table, you're stuck.
A more flexible, but more difficult approach is outlined in PHOENIX-4596.

  was:
By declaring the max number of columns on a base table, we can optimize the storage for SINGLE_CELL_ARRAY_WITH_OFFSETS
by not storing null values for the columns preceding the initial column of a view. This will
make a huge difference in storage when you have a base table with many views. For example:

{code}
-- Declare that the base table will have no more than 10 columns
CREATE IMMUTABLE TABLE base (k1 VARCHAR, prefix CHAR(3) v1 DATE,
    CONSTRAINT pk PRIMARY KEY (k1, prefix))
    MULTI_TENANT = true,
    MAX_COLUMNS = 10;
CREATE VIEW v1(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR)
    AS SELECT * FROM base WHERE prefix = 'A00';
CREATE VIEW v2(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR);
    AS SELECT * FROM base WHERE prefix = 'A10';
...
{code}

As the number of views grow, the difference between the base table column encoding (column
#1) and the starting column number of the view (since the starting offset is determined by
an incrementing value on the base table) will increase. This bloats the storage as we need
to store null values for column encodings between the base table column and the starting column
of the view.

Instead, we'll pass through the MAX_COLUMNS value for queries and anything column encoding
less than this we know it'll be at the start. Anything greater and we'll start the search
from <column encoding> - <minimum view column encoding>.


> Declare maximum columns to ensure storage is dense when table has many views
> ----------------------------------------------------------------------------
>
>                 Key: PHOENIX-4550
>                 URL: https://issues.apache.org/jira/browse/PHOENIX-4550
>             Project: Phoenix
>          Issue Type: Improvement
>            Reporter: James Taylor
>            Priority: Major
>
> By declaring the max number of columns on a base table, we can optimize the storage for
SINGLE_CELL_ARRAY_WITH_OFFSETS by not storing null values for the columns preceding the initial
column of a view. This will make a huge difference in storage when you have a base table with
many views. For example:
> {code}
> -- Declare that the base table will have no more than 10 columns
> CREATE IMMUTABLE TABLE base (k1 VARCHAR, prefix CHAR(3) v1 DATE,
>     CONSTRAINT pk PRIMARY KEY (k1, prefix))
>     MULTI_TENANT = true,
>     MAX_COLUMNS = 10;
> CREATE VIEW v1(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR)
>     AS SELECT * FROM base WHERE prefix = 'A00';
> CREATE VIEW v2(k2 VARCHAR PRIMARY KEY, v2 VARCHAR, v3 VARCHAR);
>     AS SELECT * FROM base WHERE prefix = 'A10';
> ...
> {code}
> As the number of views grow, the difference between the base table column encoding (column
#1) and the starting column number of the view (since the starting offset is determined by
an incrementing value on the base table) will increase. This bloats the storage as we need
to store null values for column encodings between the base table column and the starting column
of the view.
> Instead, we'll pass through the MAX_COLUMNS value for queries and anything column encoding
less than this we know it'll be at the start. Anything greater and we'll start the search
from <column encoding> - <minimum view column encoding>.
> The downside of this approach is if you run out of columns in the base table, you're
stuck. A more flexible, but more difficult approach is outlined in PHOENIX-4596.



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