Add 2 new TabletReader APIs: stripesMetadata and stripeGroupsMetadata (facebookincubator#126)

Summary:

These 2 new APIs will allow clients to get insights into stripes and stripe groups metadata, e.g., offset, size, etc.

This information can be useful in use cases like `nimble_dump` where we want to know the sizes of these sections in the Nimble file.

Differential Revision: D67957498

Author: Chongfeng Hu

dwio/nimble/tablet/TabletReader.cpp

@@ -26,7 +26,9 @@
 #include "folly/io/Cursor.h"
 
 #include <algorithm>
+#include <iterator>
 #include <limits>
+#include <memory>
 #include <numeric>
 #include <optional>
 #include <tuple>
@@ -325,6 +327,10 @@ TabletReader::TabletReader(
     NIMBLE_CHECK(
         stripes->offset() + readSize >= fileSize,
         "Incomplete stripes metadata.");
+    stripesMetadata_ = std::make_unique<MetadataSection>(
+        stripes->offset(),
+        stripes->size(),
+        static_cast<CompressionType>(stripes->compression_type()));
     stripes_ = std::make_unique<MetadataBuffer>(
         memoryPool_,
         footerIOBuf,
@@ -340,6 +346,16 @@ TabletReader::TabletReader(
             (stripeGroups->size() ==
              *stripesRoot->group_indices()->rbegin() + 1),
         "Unexpected stripe group count");
+    std::transform(
+        stripeGroups->cbegin(),
+        stripeGroups->cend(),
+        std::back_inserter(stripeGroupsMetadata_),
+        [](const auto& stripeGroup) {
+          return MetadataSection{
+              stripeGroup->offset(),
+              stripeGroup->size(),
+              static_cast<CompressionType>(stripeGroup->compression_type())};
+        });
 
     // Always eagerly load if it's the only stripe group and is already
     // fetched

dwio/nimble/tablet/TabletReader.h

@@ -14,7 +14,10 @@
  * limitations under the License.
  */
 #pragma once
+
+#include <memory>
 #include <span>
+#include <vector>
 
 #include "dwio/nimble/common/Checksum.h"
 #include "dwio/nimble/common/Types.h"
@@ -252,6 +255,14 @@ class TabletReader {
       const StripeIdentifier& stripe,
       std::span<const uint32_t> streamIdentifiers) const;
 
+  const MetadataSection* stripesMetadata() const {
+    return stripesMetadata_.get();
+  }
+
+  std::span<const MetadataSection> stripeGroupsMetadata() const {
+    return stripeGroupsMetadata_;
+  }
+
   std::unordered_map<std::string, MetadataSection> optionalSections() const {
     return optionalSections_;
   }
@@ -354,6 +365,8 @@ class TabletReader {
   uint32_t stripeCount_{0};
   const uint32_t* stripeRowCounts_{nullptr};
   const uint64_t* stripeOffsets_{nullptr};
+  std::unique_ptr<MetadataSection> stripesMetadata_;
+  std::vector<MetadataSection> stripeGroupsMetadata_;
   std::unordered_map<std::string, MetadataSection> optionalSections_;
   mutable folly::Synchronized<
       std::unordered_map<std::string, std::unique_ptr<MetadataBuffer>>>