Hi Sreeparna,
As suggested in the earlier e-mail, we would not expect to see different
performance in UNION ALL than in a simple scan. Clearly you've found some kind
of issue. The next step is to investigate that issue, which is a bit hard to do
over e-mail.
Please file a JIRA ticket to describe the issue and provide a reproducible test
case including query and data. If your data is sensitive, please create a dummy
data set, or use the provided TPC-H data set to recreate the issue. We can then
take a look to see what might be happening.
Thanks,
- Paul
On Thursday, April 23, 2020, 10:18:13 AM PDT, sreeparna bhabani
<[email protected]> wrote:
Hi Team,
In addition to the below mail I have another finding. Please consider below
scenarios. The first 2 scenarios are giving expected results in terms of
performance. But we are not getting expected performance for 3rd scenario which
is UNION ALL with 2 different types of datasets.
Scenario 1- Parquet UNION ALL Parquet
Individual execution time of 1st query - 5 secsIndividual execution time of 2nd
query - 5 secsUNION ALL of both queries execution time - 10 secs
Scenario 2 - DB query UNION ALL DB queryIndividual execution time of 1st query
- 5 secsIndividual execution time of 2nd query - 5 secsUNION ALL of both
queries execution time - 10 secs
Scenario 3 - Parquet UNION ALL DB query
Individual execution time of 1st query - 5 secsIndividual execution time of 2nd
query - 1 secUNION ALL execution time - 20 secsIdeally the execution time
should not be more than 6 secs.
May I request you to check whether the UNION ALL performance of 3rd scenario is
expected with different dataset types.
Please suggest if there is any specific way to bring down the execution time of
3rd scenario.
Thanks in advance.
Sreeparna Bhabani
On Thu, 23 Apr 2020, 12:18 sreeparna bhabani, <[email protected]>
wrote:
Hi Team,
Apart from the below issue I have another question.
Is there any relation between number of row groups and performance ?
In the below query the number of files is 13 and numRowGroups is 69. Is the
UNION ALL takes more time if the number of rowgroup is high like that.
Please note that the individual Parquet query takes 6 secs. But UNION ALL takes
20 secs. Details are given in trail mail.
Thanks,Sreeparna Bhabani
On Thu, 23 Apr 2020, 11:08 sreeparna bhabani, <[email protected]> wrote:
Hi Paul,
Please find the details below. We are using 2 drillbits. Heap memory 16 G, Max
direct memory 32 G. One query selects from Parquet. Another one selects fron
JDBC. The parquet file size is 849 MB. It is UNION ALL. There is not sorting.
Single parquet query-Total execution time - 6.6 secScan time - 0.152 secScreen
wait time - 5.3 sec
Single JDBC query-Total execution time - 0.261 secJDBC scan - 0.152 secScreen
wait - 0.004 sec
Union all query -Execution time - 21. 118 secScreen wait time - 5.351
secParquet scan - 15.368 secUnordered receiver wait time - 14.41 sec
Thanks,Sreeparna Bhabani
On Thu, 23 Apr 2020, 10:43 Paul Rogers, <[email protected]> wrote:
Hi Sreeparna,
The short answer is it *should* work: a UNION ALL is simply an append. (Be sure
you are not using a plain UNION as that needs to do more work to remove
duplicates.)
Since you are seeing unexpected behavior, we may have some kind of issue to
investigate and perhaps fix. Always hard to do over e-mail, but let's see what
we can do.
The first question is to understand the full query: are you doing more than a
simple scan of two files and a UNION ALL? Are there sorts or joins involved?
The best place to start to investigate performance issues is the query profile,
which it looks like you are doing. What is the time for the scans if you run
each of the two scans separately? You said that they take 8 and 1 seconds. Is
that for the whole query or just the scan operators?
Then, when you run the UNION ALL, again looking at the scan operators, is there
any difference in run times? If the scans take longer, that is one thing to
investigate. If the scans take the same amount of time, what other operator(s)
are taking the rest of the time? Your note suggests that it is the scan taking
the time. But, there should be two scan operators: one for each file. How is
the time divided between them?
How large are the data files? Using what storage system? How many Drillbits?
How much memory?
Thanks,
- Paul
On Wednesday, April 22, 2020, 11:32:24 AM PDT, sreeparna bhabani
<[email protected]> wrote:
Hi Team,
I reach out to you for a specific problem regarding UNION ALL. There is one
UNION ALL statement which combines 2 queries. The individual queries are
taking 8 secs and 1 sec respectively. But UNION ALL takes 30 secs.
PARQUET_SCAN_ROW_GROUP takes the maximum time. Apache drill version is 1.17.
Please help to suggest how to improve this UNION ALL performance. We are
using parquet file.
Thanks,
Sreeparna Bhabani
