如上图所示IMDRelation作为Interface for relations in the metadata cache，其定义了Storage type of a relation表的存储类型，如下所示：
enum Erelstoragetype {
ErelstorageHeap,
ErelstorageAppendOnlyCols,
ErelstorageAppendOnlyRows,
ErelstorageAppendOnlyParquet,
ErelstorageExternal,
ErelstorageVirtual,
ErelstorageSentinel
};下面是ErelstorageHeap存储类型所涉及到的代码：
- CTranslatorQueryToDXL::TranslateCTASToDXL Translate a CTAS 设定CDXLLogicalCTAS类的存储类型
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据存储类型字符获取其Erelstoragetype枚举类型
- CXformUtils::PexprBuildIndexPlan Construct an expression representing a new access path using the given functors for operator constructors and rewritten access path. Non-heap tables not supported for GiST 非heap表不支持GiST判定
下面是ErelstorageAppendOnlyCols存储类型所涉及到的代码：
- CTranslatorQueryToDXL::GetDXLCtasOptionArray Translate CTAS storage options 根据存储选项判定存储类型
- CTranslatorRelcacheToDXL::RetrieveRelColumns Get relation columns AO表需要添加系统列
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据存储类型字符获取其Erelstoragetype枚举类型
- CTableDescriptor::IsAORowOrColTable 判定是否是AO表
下面是ErelstorageAppendOnlyRows存储类型所涉及到的代码：
- CTranslatorQueryToDXL::GetDXLCtasOptionArray Translate CTAS storage options 根据存储选项判定存储类型
- CTranslatorRelcacheToDXL::RetrieveRelColumns Get relation columns AO表需要添加系统列
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据存储类型字符获取其Erelstoragetype枚举类型
- CTableDescriptor::IsAORowOrColTable 判定是否是AO表
- CUtils::FGeneratePartOid generate part oid 判定InsertSortOnRows
- CPhysicalDML::FInsertSortOnRows Do we need to sort on insert
下面是ErelstorageAppendOnlyParquet存储类型所涉及到的代码：
- CTranslatorQueryToDXL::GetDXLCtasOptionArray Translate CTAS storage options 根据存储选项判定存储类型
- CUtils::FGeneratePartOid generate part oid 判定InsertSortOnParquet
- CPhysicalDML::FInsertSortOnParquet Do we need to sort on parquet table
下面是ErelstorageExternal存储类型所涉及到的代码：
- CTranslatorDXLToPlStmt::TranslateDXLTblScan Translates a DXL table scan node into a TableScan node
- CTranslatorQueryToDXL::TranslateRTEToDXLLogicalGet Returns a CDXLNode representing a from relation range table entry
- CTranslatorRelcacheToDXL::RetrieveRel Retrieve a relation from the relcache given its metadata id 不为外部表的情况下get partition keys；Retrieve full part constraints partitioned tables with indexes or external partitions, returns NULL for non-partitioned tables
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据存储类型字符获取其Erelstoragetype枚举类型
- COptTasks::PrintMissingStatsWarning Print warning messages for columns with missing statistics 不为外部表时打印missing statistic信息
下面是ErelstorageVirtual存储类型所涉及到的代码：CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据存储类型字符获取其Erelstoragetype枚举类型。该枚举类型应该是不用的。
GP6与GP7存储类型对比
enum Erelstoragetype{
ErelstorageHeap,
ErelstorageAppendOnlyCols,
ErelstorageAppendOnlyRows,
ErelstorageForeign,
ErelstorageMixedPartitioned,
ErelstorageCompositeType,
ErelstorageSentinel
};下面是ErelstorageHeap存储类型所涉及到的代码：
- CTranslatorQueryToDXL::TranslateCTASToDXL Translate a CTAS 设定CDXLLogicalCTAS类的存储类型
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type
- CTranslatorRelcacheToDXL::RetrieveStorageTypeForPartitionedTable 如果rel->rd_partdesc->nparts == 0，返回ErelstorageHeap存储类型
- CXformUtils::PexprBuildIndexPlan Construct an expression representing a new access path using the given functors for operator constructors and rewritten access path. Non-heap tables not supported for GiST 非heap表不支持GiST判定
下面是ErelstorageAppendOnlyCols存储类型所涉及到的代码：
- CTranslatorQueryToDXL::GetDXLCtasOptionArray Translate CTAS storage options 根据存储选项判定存储类型
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据AM获取其Erelstoragetype枚举类型
- CTableDescriptor::IsAORowOrColTable 判定是否是AO表
下面是ErelstorageAppendOnlyRows存储类型所涉及到的代码：
- CTranslatorQueryToDXL::GetDXLCtasOptionArray Translate CTAS storage options 根据存储选项判定存储类型
- CTranslatorRelcacheToDXL::RetrieveRelStorageType Get relation storage type根据AM获取其Erelstoragetype枚举类型
- CTableDescriptor::IsAORowOrColTable 判定是否是AO表
下面是ErelstorageForeign存储类型所涉及到的代码：
- CTranslatorDXLToPlStmt::TranslateDXLTblScan Translates a DXL table scan node into a TableScan node
- TranslatorQueryToDXL::TranslateRTEToDXLLogicalGet Returns a CDXLNode representing a from relation range table entry 新建CDXLLogicalForeignGet分支
- CTranslatorRelcacheToDXL::RetrieveRel Retrieve a relation from the relcache given its metadata id. root partitions don’t have a foreign server 重要
- CTranslatorRelcacheToDXL::RetrieveRelStorageType rel->rd_rel->relkind == RELKIND_FOREIGN_TABLE分支
- CTranslatorRelcacheToDXL::RetrieveStorageTypeForPartitionedTable for partitioned tables with foreign partitions, we want to ignore the foreign partitions for determining the storage-type (unless all of the partitions are foreign) as we’ll be separating them out to different scans later in CXformExpandDynamicGetWithForeignPartitions
- CTranslatorUtils::GetTableDescr Create a DXL table descriptor from a GPDB range table entry fall back to the planner for queries on coordinator-only table if they are disabled with Orca
- CTranslatorUtils::RelContainsForeignPartitions
- COptTasks::PrintMissingStatsWarning Print warning messages for columns with missing statistics 不为外部表时打印missing statistic信息
- CTranslatorDXLToExpr::PexprLogicalGet Create a Expr logical get from a DXL logical get store array of foreign partitions
下面是ErelstorageMixedPartitioned存储类型所涉及到的代码：
- CTranslatorRelcacheToDXL::RetrieveStorageTypeForPartitionedTable mark any partitioned table with supported partitions of mixed storage types, this is more conservative for certain skans (eg: we can’t do an index scan if any partition is ao, we must only do a sequential or bitmap scan)
- CXformIndexGet2IndexOnlyScan::Exfp 判定possible_ao_table
- CXformIndexGet2IndexScan::Exfp 判定possible_ao_table
- CXformUtils::FIndexApplicable Check if an index is applicable given the required, output and scalar expression columns 判定possible_ao_table
- CXformUtils::PexprBitmapSelectBestIndex Given conjuncts of supported predicates, select the best index and construct a bitmap index path expression. Return unused predicates as residuals 判定possible_ao_table
下面是ErelstorageCompositeType存储类型所涉及到的代码：CTranslatorRelcacheToDXL::RetrieveRelStorageType中对应RELKIND_COMPOSITE_TYPE获取存储类型ErelstorageCompositeType
从上面的对比可以看出AP7将分区表子分区混合存储这种情况单独作为了一种存储类型ErelstorageMixedPartitioned。