[IMPALA-12142] Default fetch_size of 10240 is suboptimal

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: Impala 4.3.0
• Component/s: Clients
• Labels: performance
• Epic Color: ghx-label-5
• Assignee: Unassigned
• Reporter: Csaba Ringhofer
• Created: 15/May/23 12:18
• Updated: 02/Jun/23 16:21
• Resolved: 16/May/23 10:09

Description

While working on IMPALA-12138 it turned out that the default settings of batch_size=1024 and fetch_size=10240 are not ideal for the coordinator (RowMaterializationTimer). My guess for the cause is that HS2 results vectors are rounded up to power of 2 sizes leading to extra allocations and copying.

query: select * from tpch_parquet.lineitem
RowMaterializationTimer (before and after IMPALA-12138)
fetch_size=10240: 3.6s ->3.2s
fetch_size=8192: 2.8s->2.6s

Issue Links

• relates to: IMPALA-9818 Add fetch size as option to impala shell
• relates to: IMPALA-12138 Suboptimal vector allocation of HS2 results