Support memory only mode for StorageJoin and StorageSet.

[Vxider]

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Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

Support for disabling persistency for StorageJoin and StorageSet, this feature is controlled by setting disable_set_and_join_persistency. And this PR solved issue #6318.

Detailed description / Documentation draft:

[alexey-milovidov]

Why support both query-level and table-level settings?
Usage of query-level settings is inconvenient for CREATE TABLE.

[alexey-milovidov]

I'd stick with table-level settings.

[Vxider]

I have pushed a new commit that only use table-level settings. And also add functional tests.

[alexey-milovidov]

Need to add a test.
A functional test with DEATCH/ATTACH TABLE should suffice.

[alexey-milovidov]

There is something related to DatabaseAtomic...

[alexey-milovidov]

Now we have two identical settings files for Set and Join.
This is reasonable if we expect to have more settings that will be distinct for Set and Join. Ok...

[alexey-milovidov]

What did I mean... we can insert some data,
validate that it will be present after DETACH/ATTACH if disable_persistency = 0
and validate that table will be empty after DETACH/ATTACH otherwise.

PS. Maybe better to name a setting persistent with default value 1?

[Vxider]

I have pushed a commit to rename disable_persistency to persistent with default value 1. And update the tests.

[alexey-milovidov]

@tavplubix about DETACH/ATTACH sequence in DatabaseAtomic - is there any caveats, what should we do?

[tavplubix]

@tavplubix about DETACH/ATTACH sequence in DatabaseAtomic - is there any caveats, what should we do?

Test failure can be fixed by using short attach syntax (ATTACH TABLE set; instead of ATTACH TABLE set (x String) ENGINE = Set() SETTINGS disable_persistency=1;). Another way to fix it is to specify table UUID explicitly (e.g. CREATE TABLE set UUID '00001493-1000-4000-8000-000000000001' (x String) ENGINE = Set() SETTINGS disable_persistency=1;) and use the same UUID in ATTACH query.

As for DETACH/ATTACH sequence, it should work fine if no queries are using the table after DETACH. Otherwise, Cannot attach table exception will be thrown to avoid race condition.

[tavplubix]

Probably we should allow attaching another instance of storage if it doesn't store data on disk, but I'm not sure.

[alexey-milovidov]

test_rename_column

Already fixed.