Use valid compression method in brin_form_tuple

tvondra · tvondra · commit 882b2cdc08c4 · 2021-03-21T00:28:34.000+01:00
When compressing the BRIN summary, we can't simply use the compression method from the indexed attribute. The summary may use a different data type, e.g. fixed-length attribute may have varlena summary, leading to compression failures. For the built-in BRIN opclasses this happens to work, because the summary uses the same data type as the attribute. When the data types match, we can inherit use the compression method specified for the attribute (it's copied into the index descriptor). Otherwise we don't have much choice and have to use the default one. Author: Tomas Vondra Reviewed-by: Justin Pryzby <pryzby@telsasoft.com> Discussion: https://postgr.es/m/e0367f27-392c-321a-7411-a58e1a7e4817%40enterprisedb.com
diff --git a/src/backend/access/brin/brin_tuple.c b/src/backend/access/brin/brin_tuple.c
@@ -213,10 +213,22 @@ brin_form_tuple(BrinDesc *brdesc, BlockNumber blkno, BrinMemTuple *tuple,
 				(atttype->typstorage == TYPSTORAGE_EXTENDED ||
 				 atttype->typstorage == TYPSTORAGE_MAIN))
 			{
+				Datum	cvalue;
+				char	compression;
 				Form_pg_attribute att = TupleDescAttr(brdesc->bd_tupdesc,
 													  keyno);
-				Datum		cvalue = toast_compress_datum(value,
-														  att->attcompression);
+
+				/*
+				 * If the BRIN summary and indexed attribute use the same data
+				 * type, we can use the same compression method. Otherwise we
+				 * have to use the default method.
+				 */
+				if (att->atttypid == atttype->type_id)
+					compression = att->attcompression;
+				else
+					compression = GetDefaultToastCompression();
+
+				cvalue = toast_compress_datum(value, compression);
 
 				if (DatumGetPointer(cvalue) != NULL)
 				{
