Fix right offset for reading LowCardinality dictionary from remote fs in case if right mark was in the middle of compressed block.

src/Formats/MarkInCompressedFile.h

@@ -28,6 +28,11 @@ struct MarkInCompressedFile
         return !(*this == rhs);
     }
 
+    auto asTuple() const
+    {
+        return std::make_tuple(offset_in_compressed_file, offset_in_decompressed_block);
+    }
+
     String toString() const
     {
         return "(" + DB::toString(offset_in_compressed_file) + "," + DB::toString(offset_in_decompressed_block) + ")";

src/Storages/MergeTree/MergeTreeReaderStream.cpp

@@ -135,7 +135,7 @@ void MergeTreeReaderStream::init()
 }
 
 
-size_t MergeTreeReaderStream::getRightOffset(size_t right_mark_non_included)
+size_t MergeTreeReaderStream::getRightOffset(size_t right_mark)
 {
     /// NOTE: if we are reading the whole file, then right_mark == marks_count
     /// and we will use max_read_buffer_size for buffer size, thus avoiding the need to load marks.
@@ -144,70 +144,83 @@ size_t MergeTreeReaderStream::getRightOffset(size_t right_mark_non_included)
     if (marks_count == 0)
         return 0;
 
-    assert(right_mark_non_included <= marks_count);
+    assert(right_mark <= marks_count);
 
-    size_t result_right_offset;
-    if (0 < right_mark_non_included && right_mark_non_included < marks_count)
+    if (0 < right_mark && right_mark < marks_count)
     {
         /// Find the right border of the last mark we need to read.
         /// To do that let's find the upper bound of the offset of the last
         /// included mark.
 
-        /// In LowCardinality dictionary and in values of Sparse columns
-        /// several consecutive marks can point to the same offset.
-        ///
-        /// Example:
-        ///  Mark 186, points to [2003111, 0]
-        ///  Mark 187, points to [2003111, 0]
-        ///  Mark 188, points to [2003111, 0] <--- for example need to read until 188
-        ///  Mark 189, points to [2003111, 0] <--- not suitable, because have same offset
-        ///  Mark 190, points to [2003111, 0]
-        ///  Mark 191, points to [2003111, 0]
-        ///  Mark 192, points to [2081424, 0] <--- what we are looking for
-        ///  Mark 193, points to [2081424, 0]
-        ///  Mark 194, points to [2081424, 0]
+        if (is_low_cardinality_dictionary)
+        {
 
-        /// Also, in some cases, when one granule is not-atomically written (which is possible at merges)
-        /// one granule may require reading of two dictionaries which starts from different marks.
-        /// The only correct way is to take offset from at least next different granule from the right one.
-        /// So, that's why we have to read one extra granule to the right,
-        /// while reading dictionary of LowCardinality.
+            /// In LowCardinality dictionary several consecutive marks can point to the same offset.
+            ///
+            /// Also, in some cases, when one granule is not-atomically written (which is possible at merges)
+            /// one granule may require reading of two dictionaries which starts from different marks.
+            /// The only correct way is to take offset from at least next different granule from the right one.
+            /// So, that's why we have to read one extra granule to the right,
+            /// while reading dictionary of LowCardinality.
+            ///
+            /// Example:
+            /// Mark 0, points to [0, 8]
+            /// Mark 1, points to [0, 8]
+            /// Mark 2, points to [0, 8]
+            /// Mark 3, points to [0, 8]
+            /// Mark 4, points to [42336, 2255]
+            /// Mark 5, points to [42336, 2255]  <--- for example need to read until 5
+            /// Mark 6, points to [42336, 2255]  <--- not suitable, because have same offset
+            /// Mark 7, points to [84995, 7738]  <--- next different mark
+            /// Mark 8, points to [84995, 7738]
+            /// Mark 9, points to [126531, 8637] <--- what we are looking for
 
-        /// If right_mark_non_included has non-zero offset in decompressed block, we have to
-        /// read its compressed block in a whole, because it may consist data from previous granule.
+            auto indices = collections::range(right_mark, marks_count);
+            auto next_different_mark = [&](auto lhs, auto rhs)
+            {
+                return marks_loader.getMark(lhs).asTuple() < marks_loader.getMark(rhs).asTuple();
+            };
+            auto it = std::upper_bound(indices.begin(), indices.end(), right_mark, std::move(next_different_mark));
+
+            if (it == indices.end())
+                return file_size;
+
+            right_mark = *it;
+        }
+
+        /// This is a good scenario. The compressed block is finished witin the right mark,
+        /// and previous mark was different.
+        if (marks_loader.getMark(right_mark).offset_in_decompressed_block == 0
+            && marks_loader.getMark(right_mark) != marks_loader.getMark(right_mark - 1))
+            return marks_loader.getMark(right_mark).offset_in_compressed_file;
+
+        /// If right_mark has non-zero offset in decompressed block, we have to
+        /// read its compressed block in a whole, because it may consist of data from previous granule.
         ///
         /// For example:
-        /// Mark 10: (758287, 0)      <--- right_mark_included
-        /// Mark 11: (908457, 53477)  <--- right_mark_non_included
-        /// Mark 12: (1064746, 20742) <--- what we are looking for
-        /// Mark 13: (2009333, 40123)
+        /// Mark 6, points to [42336, 2255]
+        /// Mark 7, points to [84995, 7738]  <--- right_mark
+        /// Mark 8, points to [84995, 7738]
+        /// Mark 9, points to [126531, 8637] <--- what we are looking for
         ///
-        /// Since mark 11 starts from offset in decompressed block 53477,
-        /// it has some data from mark 10 and we have to read
-        /// compressed block  [908457; 1064746 in a whole.
+        /// Since mark 7 starts from offset in decompressed block 7738,
+        /// it has some data from mark 6 and we have to read
+        /// compressed block  [84995; 126531 in a whole.
 
-        size_t right_mark_included = right_mark_non_included - 1;
-        if (is_low_cardinality_dictionary || marks_loader.getMark(right_mark_non_included).offset_in_decompressed_block != 0)
-            ++right_mark_included;
-
-        auto indices = collections::range(right_mark_included, marks_count);
-        auto it = std::upper_bound(indices.begin(), indices.end(), right_mark_included,
-            [&](auto lhs, auto rhs)
-            {
-                return marks_loader.getMark(lhs).offset_in_compressed_file < marks_loader.getMark(rhs).offset_in_compressed_file;
-            });
+        auto indices = collections::range(right_mark, marks_count);
+        auto next_different_compressed_offset = [&](auto lhs, auto rhs)
+        {
+            return marks_loader.getMark(lhs).offset_in_compressed_file < marks_loader.getMark(rhs).offset_in_compressed_file;
+        };
+        auto it = std::upper_bound(indices.begin(), indices.end(), right_mark, std::move(next_different_compressed_offset));
 
         if (it != indices.end())
-            result_right_offset = marks_loader.getMark(*it).offset_in_compressed_file;
-        else
-            result_right_offset = file_size;
+            return marks_loader.getMark(*it).offset_in_compressed_file;
     }
-    else if (right_mark_non_included == 0)
-        result_right_offset = marks_loader.getMark(right_mark_non_included).offset_in_compressed_file;
-    else
-        result_right_offset = file_size;
+    else if (right_mark == 0)
+        return marks_loader.getMark(right_mark).offset_in_compressed_file;
 
-    return result_right_offset;
+    return file_size;
 }
 
 void MergeTreeReaderStream::seekToMark(size_t index)

src/Storages/MergeTree/MergeTreeReaderStream.h

@@ -49,7 +49,7 @@ public:
 
 private:
     void init();
-    size_t getRightOffset(size_t right_mark_non_included);
+    size_t getRightOffset(size_t right_mark);
 
     const MergeTreeReaderSettings settings;
     const ReadBufferFromFileBase::ProfileCallback profile_callback;

tests/integration/test_s3_low_cardinality_right_border/test.py

@@ -132,3 +132,24 @@ def test_s3_right_border_2(started_cluster):
     node1.query("optimize table s3_low_cardinality final")
     res = node1.query("select * from s3_low_cardinality where key = 9000")
     assert res == "9000\t9000\n"
+
+def test_s3_right_border_3(started_cluster):
+    node1.query("drop table if exists s3_low_cardinality")
+    node1.query("create table s3_low_cardinality (x LowCardinality(String)) engine = MergeTree order by tuple() settings min_bytes_for_wide_part=0, storage_policy = 's3', max_compress_block_size=10000")
+    node1.query("insert into s3_low_cardinality select toString(number % 8000) || if(number < 8192 * 3, 'aaaaaaaaaaaaaaaa', if(number < 8192 * 6, 'bbbbbbbbbbbbbbbbbbbbbbbb', 'ccccccccccccccccccc')) from numbers(8192 * 9)")
+    # Marks are:
+    # Mark 0, points to 0, 8, has rows after 8192, decompressed size 0.
+    # Mark 1, points to 0, 8, has rows after 8192, decompressed size 0.
+    # Mark 2, points to 0, 8, has rows after 8192, decompressed size 0.
+    # Mark 3, points to 0, 8, has rows after 8192, decompressed size 0.
+    # Mark 4, points to 42336, 2255, has rows after 8192, decompressed size 0.
+    # Mark 5, points to 42336, 2255, has rows after 8192, decompressed size 0.
+    # Mark 6, points to 42336, 2255, has rows after 8192, decompressed size 0.
+    # Mark 7, points to 84995, 7738, has rows after 8192, decompressed size 0.
+    # Mark 8, points to 84995, 7738, has rows after 8192, decompressed size 0.
+    # Mark 9, points to 126531, 8637, has rows after 0, decompressed size 0.
+
+    res = node1.query("select uniq(x) from s3_low_cardinality settings max_threads=2, merge_tree_min_rows_for_concurrent_read_for_remote_filesystem=1, merge_tree_min_bytes_for_concurrent_read_for_remote_filesystem=1")
+    # Reading ranges [0, 5) and [5, 9)
+
+    assert res == "23999\n"