docs/design: Support Spilling Unparalleled HashAgg#25792
docs/design: Support Spilling Unparalleled HashAgg#25792ti-chi-bot merged 8 commits intopingcap:masterfrom
Conversation
ti-chi-bot
added
the
size/M
|
|
||
| ## Impacts & Risks | ||
|
|
||
| * Memory will still grow without increasing the number of new tuples in HashMap for distinct aggregate function. |
There was a problem hiding this comment.
I don't understand this. It's seem that there is a contradiction between memory still grow and without increasing the number of new tuples.
There was a problem hiding this comment.
In fact, it is not contradict. For the distinct agg function, it is necessary to record those values that have appeared. We are using a set to record this information. This set will still grow during the aggregation process without increasing the number of new tuples in aggPartialResultMapper.
For example,
type partialResult4CountDistinctInt struct {
valSet set.Int64SetWithMemoryUsage
}
| # Proposal: Support Spilling Unparalleled HashAgg | ||
|
|
||
| - Author(s): [@wshwsh12](https://github.com/wshwsh12) | ||
| - Discussion PR: N/A |
There was a problem hiding this comment.
| - Discussion PR: N/A | |
| - Discussion PR: https://github.com/pingcap/tidb/pull/25792 |
| * When the unparallel-agg exceeds the memory quota, this feature helps reduce memory usage and run the sql successfully. | ||
| * When the parallel-agg exceeds the memory quota, the SQL will be canceled before. After the agg-concurrency args are set to 1, the SQL can run successfully. | ||
| * When the ndv of the data is low, the SQL contains distinct function will be canceled before. After the agg-concurrency args are set to 1, the SQL can run successfully. | ||
| * When the ndv of the data is high, the SQL contains distinct function will be canceled before. After the agg-concurrency args are set to 1, the SQL can be canceled successfully if there is insufficient memory. |
There was a problem hiding this comment.
Why do we need to set the concurrency-related args when there exists an aggregation function with the keyword distinct.
|
[REVIEW NOTIFICATION] This pull request has been approved by:
To complete the pull request process, please ask the reviewers in the list to review by filling The full list of commands accepted by this bot can be found here. DetailsReviewer can indicate their review by submitting an approval review. |
ti-chi-bot
added
status/LGT2
|
/merge |
|
This pull request has been accepted and is ready to merge. DetailsCommit hash: d78daac |
ti-chi-bot
added
the
status/can-merge
XuHuaiyu
added
component/docs
and removed
status/can-merge
ti-chi-bot
added
the
status/can-merge
5 participants
What problem does this PR solve?
Issue Number: close #xxx
Problem Summary:
What is changed and how it works?
Proposal: xxx
What's Changed: Design docs.
How it Works:
Related changes
pingcap/docs/pingcap/docs-cn:Release note