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From Ming Li <...@pivotal.io>
Subject [Propose] More data skipping technology for IO intensive performance enhancement
Date Sat, 02 Jul 2016 15:19:10 GMT
Data skipping technology can extremely avoiding unnecessary IO,  so it can
extremely enhance performance for IO intensive query. Including eliminating
query on unnecessary table partition according to the partition key range ,
I think more options are available now:

(1) Parquet / ORC format introduce a lightweight meta data info like
Min/Max/Bloom filter for each block, such meta data can be exploited when
predicate/filter info can be fetched before executing scan.

However now in HAWQ, all data in parquet need to be scanned into memory
before processing predicate/filter. We don't generate the meta info when
INSERT into parquet table, the scan executor doesn't utilize the meta info
neither. Maybe some scan API need to be refactored so that we can get
info before executing base relation scan.

(2) Base on (1) technology,  especially with Bloom filter, more optimizer
technology can be explored furthur. E.g. Impala implemented Runtime
),  which can be used at
- dynamic partition pruning
- converting join predicate to base relation predicate

It tell the executor to wait for one moment(the interval time can be set in
guc) before executing base relation scan, if the interested values(e.g. the
column in join predicate only have very small set) arrived in time, it can
use these value to filter this scan, if doesn't arrived in time, it scan
without this filter, which doesn't impact result correctness.

Unlike (1) technology, this technology cannot be used in any case, it only
outperform in some cases. So it just add some more query plan
choices/paths, and the optimizer need based on statistics info to calculate
the cost, and apply it when cost down.

All in one, maybe more similar technology can be adoptable for HAWQ now,
let's start to think about performance related technology, moreover we need
to instigate how these technology can be implemented in HAWQ.

Any ideas or suggestions are welcomed? Thanks.

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