Details
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Bug
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Status: Resolved
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Major
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Resolution: Won't Fix
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None
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None
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Description
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:
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;
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.