[
https://issues.apache.org/jira/browse/PHOENIX-1940?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14521086#comment-14521086
]
James Taylor commented on PHOENIX-1940:
---------------------------------------
With write-once data, we could allow NOT NULL constraints, easily enforce them
from the client, and know when all columns in the scan are NOT NULL such that
we can access the List<Cell> positionally.
But a few observations come to mind, [~lhofhansl]:
- tho it's fine to optimize, write-once data is not the best use case for HBase
IHO.
- even with a best case 60% improvement for the all in block cache scenario,
where do you think we can get the order of magnitude improvement for scans that
we really need?
> Push expected List<Cell> ordinal position in KeyValueColumnExpression
> ---------------------------------------------------------------------
>
> Key: PHOENIX-1940
> URL: https://issues.apache.org/jira/browse/PHOENIX-1940
> Project: Phoenix
> Issue Type: Bug
> Reporter: James Taylor
>
> Looks like quite a bit of time is spent in the binary search done to get the
> latest Cell value when we're evaluating expressions on the server side (up to
> 60% is spent in KeyValueUtil.getColumnLatest()). Since we know the set of
> column qualifiers being projected into the scan, we could push the expected
> position (assuming all columns have values). If the Cell is not in that
> position, we could fall back to a binary search.
> Further enhancements could be to: allow a not null constraint on KeyValue
> columns and either a) require all non null values to be provided on an
> UPSERT, or b) do a check and put to enforce it (for transactional tables this
> could be enforced).
> Additionally, the table could declare that dynamic columns are not allowed.
> If both of the above are true, then we'd be able guaranteed positional access
> the List<Cell> that we get back from an HBase Scanner.
> One further enhancement would be to collect a set of all ColumnExpression
> instances on the server side for all expressions sent over. Then, we'd bind
> them once, outside of the general expression evaluation of all expressions in
> a statement for a given row. An example of where this would save time would
> be in evaluating the following TPCH-Q1 aggregate query:
> {code}
> SELECT
> l_returnflag,
> l_linestatus,
> sum(l_quantity) as sum_qty,
> sum(l_extendedprice) as sum_base_price,
> sum(l_extendedprice * (1 - l_discount)) as sum_disc_price,
> sum(l_extendedprice * (1 - l_discount) * (1 + l_tax)) as sum_charge,
> avg(l_quantity) as avg_qty,
> avg(l_extendedprice) as avg_price,
> avg(l_discount) as avg_disc,
> count(*) as count_order
> FROM
> lineitem
> WHERE
> l_shipdate <= date '1998-12-01' - interval '90' day
> GROUP BY
> l_returnflag,
> l_linestatus
> ORDER BY
> l_returnflag,
> l_linestatus;
> {code}
> During aggregation, the KeyValueColumnExpression for l_extendedprice would be
> evaluated four times currently, once per occurrence in different SELECT
> expressions. This enhancement would cut that down to once.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
