morningman commented on pull request #3694:
URL: https://github.com/apache/incubator-doris/pull/3694#issuecomment-634526451
> Hi, @morningman I have some question about olap_scan_node, could you plz
help me figure it out?
>
> 1. what's the relationship between scanner and tablet, one tablet can be
scanned by many scanner?they are n:1 or 1:1?
> 2. what's the relationship between TPaloScanRange and ColumnValueRange, is
ColumnValueRange to deal with predicate case and TPaloScanRange can indicate
that the range a scanner need to scan from StorageEngine's prefix index?
> 3. What's the usage of function `extend_scan_key` and the config variable
`doris_scanner_row_num`?
> I would appreciate your reply, thanks~
1. scanner and tablet is `n:m` relation
2. I am not familiar with `TPaloScanRange`, need a further look...
3. `extend_scan_key` is used to extend the scan keys. `scan keys` are used
to determine the number of scanners.
For example, `WHERE a in (1,2,3) and b > 5` and `a`, `b` are key columns of
the table.
First, for `a in (1,2,3)`, the `scan keys` become: `(a=1),(a=2),(a=3)`
Second, for `b > 5`, the `scan keys` extends to `(a=1, b>5), (a=2, b>5),
(a=3, b>5)`
4. `doris_scanner_row_num` is used for priority scheduling of scanner. Doris
has a scanner thread pool that is shared by all scanners. Therefore, a
scheduling strategy is needed to prevent a scanner from occupying threads for a
long time. `doris_scanner_row_num` can control the maximum number of rows a
scanner can read in one scheduling. The details of the algorithm that are not
specific need to be understood by reading the code.
@chaoyli may understand this better. If I said something wrong, he can help
correct it.
----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
For queries about this service, please contact Infrastructure at:
[email protected]
---------------------------------------------------------------------
To unsubscribe, e-mail: [email protected]
For additional commands, e-mail: [email protected]
