fix: don't aggregate columns for clustered columnstore indexes in describe_indexes#745
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…cribe_indexes
A clustered columnstore index (type 5) stores the whole table and has no key
columns, so sys.index_columns lists every column for it. describe_indexes was
aggregating all of them into the `columns` field, which:
- is meaningless: reconciliation (index_config_changes) matches a CCI by
name and type only and never compares its columns, and
- was the underlying cause of the STRING_AGG 8000-byte overflow in dbt-msft#735 —
the nvarchar(max) cast merged there stops the *error* but still builds a
~25 KB column list on every reconcile of a wide table.
Guard the key-column aggregation with `i.[type] <> 5` so a CCI reports no
columns. The nvarchar(max) cast is kept as defense for wide *nonclustered*
columnstore indexes (type 6), whose columns are genuine user-chosen identity.
Extends the wide-columnstore functional test to assert describe_indexes
reports no columns for the CCI.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Follow-up to #735. Resolve #744
A clustered columnstore index (type 5) stores the whole table and has no key columns, so sys.index_columns lists every column for it. sqlserver__describe_indexes was aggregating all of them into the columns field, which is (a) meaningless — reconciliation matches a CCI by name/type and never compares its columns — and (b) the underlying cause of the STRING_AGG 8000-byte overflow.
Change: guard the key-column aggregation with i.[type] <> 5 so a CCI reports no columns. The nvarchar(max) cast is kept as defense for wide nonclustered columnstore indexes (type 6), whose columns are genuine user-chosen identity.
Testing: extends the existing wide-columnstore functional test with a run-operation that calls describe_indexes and asserts the CCI is described with zero columns. Existing reconcile-survival assertion unchanged. All 281 unit tests pass.
Scope is deliberately narrow: only type 5 is affected; types 1/2/6 are untouched.