Live views aren't removed after disconnection (HTTP)

[loyd]

Description
If the WATCH statement is used via HTTP interface for live views with a timeout, the live view isn't removed after disconnection.

Steps to reproduce the bug

1. Create a live view:

echo 'CREATE LIVE VIEW lv_http WITH TIMEOUT AS SELECT 1' | curl 'http://127.0.0.1:8123/?allow_experimental_live_view=1' --data-binary @-

2. Watch it:

echo 'WATCH lv_http' | curl 'http://127.0.0.1:8123/?allow_experimental_live_view=1' --data-binary @-
1        1

3. Send SIGINT.
4. Check tables after at least 15s:

6c59ef6be4f2 :) SHOW TABLES;
┌─name────┐
│ lv_http │
└─────────┘

Which ClickHouse server version to use?
Checked 21.2.2.8.

Expected behavior
The live view should be removed after a timeout.

[vzakaznikov]

This most likely means that the HTTP connection is not closed on the server and the live output stream never gets destroyed.

[vzakaznikov]

@loyd, could you please try specifying JSONEachRowWithProgress as the output format? This will force the connection use heartbeats to keep HTTP connection alive. When client abruptly disappears it will force a fault on the next hearbeat and the output stream should close. So the max expected time for the table to be deleted will be heartbeat period + timeout period.

[loyd]

Yep, with JSONEachRowWithProgress it works as expected.

I write a library based on HTTP + RowBinary. I can switch to JSONEachRowWithProgress for WATCH, but it's not very convenient. Maybe I should shutdown the connection?

[loyd]

But emergencies are still possible, so the use of JSONEachRowWithProgress seems to be a more reliable method.

[vzakaznikov]

But emergencies are still possible, so the use of JSONEachRowWithProgress seems to be a more reliable method.

Yes, you should only use JSONEachRowWithProgress format for WATCH queries over the HTTP connection. First, because HTTP connection needs heartbeat messages send periodically from the server to the client, and second, that's the only way the server can detect abruptly terminated client connections.

[vzakaznikov]

@alexey-milovidov, we can close this issue as the behavior is not a bug in LIVE VIEW tables. The only potential issue is the inability of the ClickHouse server to detect dropped HTTP connections.

[loyd]

After #42173 it cannot be removed even with JSONEachRowWithProgress.

Should we reopen the issue or create a new one?

[vzakaznikov]

Hi @loyd, the WITH TIMEOUT has been removed and temporary LIVE VIEWs are not supported anymore.
That decision was made by the core team. I have not looked into if you can use TEMPORARY TABLEs instead. However, original WITH TIMEOUT live views were not session dependent and would be only automatically removed when there was no active WATCH queries.

#42173
#52333

[loyd]

@vzakaznikov, thx for the response. Do you know whether WINDOW VIEW can be used to emulate the semantic of LIVE VIEW?