[KUDU-2226] Tablets with too many DRSs will cause a huge DMS memory overhead

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.3.0
• Fix Version/s: 1.12.0
• Environment: CentOS6.5 Linux 2.6.32-431 ; Kudu1.3.0 ; GitCommit 00813f96b9cb
• Assignee: Unassigned
• Reporter: ZhangZhen
• Created: 30/Nov/17 03:37
• Updated: 05/May/20 00:34
• Resolved: 05/May/20 00:34

Description

I have a table with 10M rows in total and has been hash partitioned to 16 buckets. Each tablet has about 100MB on disk size according to the /tablets Web UI. Everyday 50K new rows will be inserted into this table, and about 5M rows of this table will be updated, that's about half of rows in total, each row will be updated only once.

Then I found something strange, from the /mem-trackers UI of TS, I found every tablet of this table occupied about 900MB memory, mainly occupied by DeltaMemStore, the peak memory consumption is about 1.8G.

I don't understand why the DeltaMemStore will cost so much memory, 900MB DMS vs 100MB on disk size, that seems strange to me. What's more, I found these DMS will be flushed very slowly, so for a long time these memory are occupied, which cause "Soft memory limit exceeded" in the TS, and in result cause "Rejecting consensus request".