[IMPALA-2568] ExecuteStatement RPC (and beeswax query() RPC) should not block

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: Impala 2.0
• Component/s: Clients
• Labels: usability
• Target Version: Product Backlog
• Assignee: Unassigned
• Reporter: casey
• Created: 19/Oct/15 23:21
• Updated: 6 days ago 22:35

Description

Even though the client api is intended to be non-blocking for statement execution requests, Impala still blocks for some part (or parts) of query execution. The client cannot know how long a request will block which makes setting a good timeout value very difficult.

Clients now have these two options:

1) Set an long enough timeout to allow for execution. The value could be 5 or more mins. But if a timeout occurs, the user needs to investigate if the query was still executing. Also a real network timeout means a very long wait interval before retrying the request.

2) Don't set a timeout. Most of the time this works well but when a real networking problem happens the client will hang forever.

https://github.com/cloudera/impyla/issues/7 shows an example of such problems. Impyla ended up going with option #2.

I've found #2 to be a big burden. To avoid hanging, any request to the server needs to be done in a separate thread which is then monitored and timed out. Option #1 is an easier way of avoiding hangs.

Issue Links

• blocks: IMPALA-718 ExecuteStatement (HS2) and query (beeswax) are supposed to be non-blocking RPC but for DDL, they block
• blocks: IMPALA-915 Ability to cancel queries while in the FE.
• is related to: IMPALA-7555 impala-shell can hang in connect in certain cases
• is related to: IMPALA-10811 RPC to submit query getting stuck for AWS NLB forever.
• relates to: IMPALA-7312 Non-blocking mode for Fetch() RPC
• relates to: IMPALA-9239 Add timeout for query analysis/planning

Sub-Tasks

• Return a profile for queries during planning: Open
• Admission control queuing should be asynchronous: Resolved
• ExecuteStatement (HS2) and query (beeswax) are supposed to be non-blocking RPC but for DDL, they block: Open
• Ability to cancel queries while in the FE.: In Progress
• Analysis and planning should happen asynchronously: Open
• Use an internal representation of query states in ClientRequestState: Resolved