Some changes

src/Storages/MergeTree/MergeTreeData.cpp

@@ -3055,6 +3055,36 @@ MergeTreeData::selectTTLEntryForTTLInfos(const IMergeTreeDataPart::TTLInfos & tt
     return max_max_ttl ? *best_entry_it : std::optional<TTLDescription>();
 }
 
+
+CompressionCodecPtr MergeTreeData::getCompressionCodecForPart(size_t part_size_compressed, const IMergeTreeDataPart::TTLInfos & ttl_infos, time_t current_time) const
+{
+
+    time_t max_max_ttl = 0;
+    TTLDescriptions::const_iterator best_entry_it;
+    auto metadata_snapshot = getInMemoryMetadataPtr();
+
+    const auto & recompression_ttl_entries = metadata_snapshot->getRecompressionTTLs();
+    for (auto ttl_entry_it = recompression_ttl_entries.begin(); ttl_entry_it != recompression_ttl_entries.end(); ++ttl_entry_it)
+    {
+        auto ttl_info_it = ttl_infos.recompression_ttl.find(ttl_entry_it->result_column);
+        /// Prefer TTL rule which went into action last.
+        if (ttl_info_it != ttl_infos.recompression_ttl.end()
+                && ttl_info_it->second.max <= current_time
+                && max_max_ttl <= ttl_info_it->second.max)
+        {
+            best_entry_it = ttl_entry_it;
+            max_max_ttl = ttl_info_it->second.max;
+        }
+    }
+
+    if (max_max_ttl)
+        return CompressionCodecFactory::instance().get(best_entry_it->recompression_codec, {});
+
+    return global_context.chooseCompressionCodec(
+        part_size_compressed,
+        static_cast<double>(part_size_compressed) / getTotalActiveSizeInBytes());
+}
+
 MergeTreeData::DataParts MergeTreeData::getDataParts(const DataPartStates & affordable_states) const
 {
     DataParts res;

src/Storages/MergeTree/MergeTreeData.h

@@ -669,6 +669,9 @@ public:
 
     std::optional<TTLDescription> selectTTLEntryForTTLInfos(const IMergeTreeDataPart::TTLInfos & ttl_infos, time_t time_of_move) const;
 
+
+    CompressionCodecPtr getCompressionCodecForPart(size_t part_size_compressed, const IMergeTreeDataPart::TTLInfos & ttl_infos, time_t current_time) const;
+
     /// Limiting parallel sends per one table, used in DataPartsExchange
     std::atomic_uint current_table_sends {0};
 

src/Storages/MergeTree/MergeTreeDataMergerMutator.cpp

@@ -284,6 +284,7 @@ bool MergeTreeDataMergerMutator::selectPartsToMerge(
                 current_time,
                 data_settings->merge_with_ttl_timeout,
                 data_settings->ttl_only_drop_parts);
+
         parts_to_merge = merge_selector.select(partitions, max_total_size_to_merge);
     }
 

src/Storages/MergeTree/MergeTreeDataMergerMutator.h

@@ -249,6 +249,7 @@ private:
 
     /// Stores the next TTL merge due time for each partition (used only by TTLMergeSelector)
     TTLMergeSelector::PartitionIdToTTLs next_ttl_merge_times_by_partition;
+
     /// Performing TTL merges independently for each partition guarantees that
     /// there is only a limited number of TTL merges and no partition stores data, that is too stale
 };

src/Storages/MergeTree/MergeTreeDataPartTTLInfo.cpp

@@ -16,6 +16,12 @@ void MergeTreeDataPartTTLInfos::update(const MergeTreeDataPartTTLInfos & other_i
         updatePartMinMaxTTL(ttl_info.min, ttl_info.max);
     }
 
+    for (const auto & [name, ttl_info] : other_infos.recompression_ttl)
+    {
+        recompression_ttl[name].update(ttl_info);
+        updatePartMinMaxTTL(ttl_info.min, ttl_info.max);
+    }
+
     for (const auto & [expression, ttl_info] : other_infos.moves_ttl)
     {
         moves_ttl[expression].update(ttl_info);
@@ -77,6 +83,7 @@ void MergeTreeDataPartTTLInfos::read(ReadBuffer & in)
             ttl_info.max = move["max"].getUInt();
             String expression = move["expression"].getString();
             recompression_ttl.emplace(expression, ttl_info);
+            updatePartMinMaxTTL(ttl_info.min, ttl_info.max);
         }
     }
 }