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 predicate/filter 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 filtering(*https://www.cloudera.com/documentation/enterprise/latest/topics/impala_runtime_filtering.html <https://www.cloudera.com/documentation/enterprise/latest/topics/impala_runtime_filtering.html>* ), 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.
