Follow-up for compressed chunk collation #4236

Add a changelog message and add a check for broken chunks to the update
script.

CHANGELOG.md

@@ -6,6 +6,8 @@ accidentally triggering the load of a previous DB version.**
 
 ## Unreleased
 
+If you use compression with a non-default collation on a segmentby-column you might have to recompress the affected hypertable.
+
 **Features**
 * #4120 Add logging for retention policy
 * #4169 Add support for chunk exclusion on DELETE to PG14
@@ -15,6 +17,7 @@ accidentally triggering the load of a previous DB version.**
 * #3899 Fix segfault in Continuous Aggregates
 * #4225 Fix TRUNCATE error as non-owner on hypertable
 * #4259 Fix logic bug in extension update script
+* #4236 Fix potential wrong order of results for compressed hypertable with a non-default collation
 
 **Thanks**
 * @jsoref for fixing various misspellings in code, comments and documentation

scripts/test_update_from_tag.sh

@@ -88,7 +88,7 @@ docker_pgcmd() {
 
 docker_pgscript() {
     local database=${3:-single}
-    docker_exec $1 "psql -h localhost -U postgres -d $database $PGOPTS -v ON_ERROR_STOP=1 -f $2"
+    docker_exec $1 "psql --set VERBOSITY=verbose --set ECHO=all -h localhost -U postgres -d $database $PGOPTS -v ON_ERROR_STOP=1 -f $2"
 }
 
 docker_pgtest() {

sql/updates/latest-dev.sql

@@ -5,3 +5,70 @@ AS '@MODULE_PATHNAME@', 'ts_relation_size' LANGUAGE C VOLATILE;
 DROP VIEW IF EXISTS _timescaledb_internal.hypertable_chunk_local_size;
 DROP INDEX IF EXISTS _timescaledb_catalog.chunk_constraint_chunk_id_dimension_slice_id_idx;
 CREATE INDEX chunk_constraint_dimension_slice_id_idx ON _timescaledb_catalog.chunk_constraint (dimension_slice_id);
+
+-- Report the compressed chunks that have a wrong collation. See https://github.com/timescale/timescaledb/pull/4236
+DO $$
+DECLARE
+    _hypertable regclass;
+    _column_name text;
+    _chunks regclass[];
+BEGIN
+    FOR _hypertable,
+    _column_name,
+    _chunks IN
+-- We materialize this CTE so that the filter on dropped chunks works
+-- first, and we don't try to look up regclass for dropped chunks.
+WITH chunk AS MATERIALIZED (
+        SELECT
+            format('%I.%I', compressed_chunk.schema_name, compressed_chunk.table_name) compressed_chunk,
+            format('%I.%I', normal_chunk.schema_name, normal_chunk.table_name) normal_chunk,
+            normal_chunk.hypertable_id hypertable_id
+        FROM
+            _timescaledb_catalog.chunk normal_chunk,
+            _timescaledb_catalog.chunk compressed_chunk
+        WHERE
+            normal_chunk.compressed_chunk_id = compressed_chunk.id
+            AND NOT normal_chunk.dropped
+),
+col AS (
+    SELECT
+        hypertable_id,
+        normal_chunk,
+        normal_column.attname column_name
+    FROM
+        chunk,
+        pg_attribute normal_column,
+        pg_attribute compressed_column
+    WHERE
+        normal_column.attrelid = normal_chunk::regclass
+        AND compressed_column.attrelid = compressed_chunk::regclass
+        AND normal_column.attname = compressed_column.attname
+        AND compressed_column.atttypid != '_timescaledb_internal.compressed_data'::regtype
+        AND normal_column.attcollation != compressed_column.attcollation
+),
+report_rows AS (
+    SELECT
+        format('%I.%I', schema_name, table_name)::regclass hypertable,
+        normal_chunk::regclass chunk,
+        column_name
+    FROM
+        col,
+        _timescaledb_catalog.hypertable
+    WHERE
+        hypertable.id = hypertable_id
+)
+SELECT
+    hypertable,
+    column_name,
+    array_agg(chunk) chunks
+FROM
+    report_rows
+GROUP BY
+    hypertable,
+    column_name LOOP
+        RAISE warning 'some compressed chunks for hypertable "%" use a wrong collation for the column "%"', _hypertable, _column_name
+            USING detail = 'This may lead to wrong order of results if you are using an index on this column of the compessed chunk.',
+            hint = format('If you experience this problem, disable compression on the table and enable it again. This will require decompressing and compressing all chunks of the table. The affected chunks are "%s".', _chunks);
+END LOOP;
+END
+$$;