ldr: it is possible to truncate a table used by LDR

[jeffswenson]

It's possible to run truncate against a table that is the source or destination for LDR. This is a problem because truncate switches which index id is used by the primary key and LDR is not set up to handle that.

$ cockroach demo --insecure --empty

CREATE DATABASE db_a; CREATE DATABASE db_b;

CREATE TABLE db_a.test_table (id INT PRIMARY KEY, value STRING);

CREATE EXTERNAL CONNECTION conn_a AS 'postgresql://root@localhost:26257/db_a?sslmode=disable';
CREATE EXTERNAL CONNECTION conn_b AS 'postgresql://root@localhost:26257/db_b?sslmode=disable';

USE db_b;
CREATE LOGICALLY REPLICATED TABLE test_table
	FROM TABLE test_table
	ON 'external://conn_a'
	WITH BIDIRECTIONAL ON 'external://conn_b';

TRUNCATE db_a.test_db;
-- This should error

Jira issue: CRDB-57681

Epic CRDB-55074

[blathers-crl]

Hi @jeffswenson, please add a branch-* label to identify the earliest affected branch for this C-bug

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[blathers-crl]

cc @cockroachdb/disaster-recovery

[jeffswenson]

Seems to be related to the declaritive schema changer:

root@127.0.0.1:26257/demoapp/db_b> SET use_declarative_schema_changer = 'off';

root@127.0.0.1:26257/demoapp/db_b> truncate db_a.test_table;
ERROR: this schema change is disallowed because table "test_table" is locked and this operation cannot automatically unlock the table
SQLSTATE: 57000
DETAIL: To unlock the table, execute `ALTER TABLE test_table SET (schema_locked = false);`
After the schema change completes, we recommend setting it back to true with `ALTER TABLE test_table SET (schema_locked = true);`.
HINT: Locking the table improves changefeed performance; see https://www.cockroachlabs.com/docs/v26.1/changefeed-best-practices.html#lock-the-schema-on-changefeed-watched-tables

root@127.0.0.1:26257/demoapp/db_b> set use_declaritive_schema-changer = 'on';
root@127.0.0.1:26257/demoapp/db_b> truncate db_a.test_table;
NOTICE: waiting for job(s) to complete: 1131309239199825921
If the statement is canceled, jobs will continue in the background.
TRUNCATE

[msbutler]

looks like @fqazi has already attempted to fix this at least for changefeeds? #152932

[jeffswenson]

I audited the underlying code. This seems to only impact the declarative schema changer. The legacy truncate implementation has a check that eventually checks for LDR jobs.

I think the declarative schema changer implementation of truncate needs to call checkTableSchemaChangePrerequisites.

[blathers-crl]

This issue has multiple T-eam labels. Please make sure it only has one, or else issue synchronization will not work correctly.

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