More comments, better code

dbms/Storages/ColumnsDescription.cpp

@@ -1,6 +1,5 @@
 #include <Storages/ColumnsDescription.h>
 
-#include <boost/algorithm/string/replace.hpp>
 #include <Parsers/ASTLiteral.h>
 #include <Parsers/ExpressionElementParsers.h>
 #include <Parsers/ExpressionListParsers.h>

dbms/Storages/MergeTree/IMergeTreeReader.h

@@ -78,6 +78,7 @@ protected:
     MarkRanges all_mark_ranges;
 
     friend class MergeTreeRangeReader::DelayedStream;
+    /// Alter conversions, which must be applied on fly if required
     MergeTreeData::AlterConversions alter_conversions;
 };
 

dbms/Storages/StorageMergeTree.cpp

@@ -241,6 +241,11 @@ void StorageMergeTree::alter(
 
         DatabaseCatalog::instance().getDatabase(table_id.database_name)->alterTable(context, table_id.table_name, metadata);
 
+        String mutation_file_name;
+        Int64 mutation_version = -1;
+        if (!maybe_mutation_commands.empty())
+            mutation_version = startMutation(maybe_mutation_commands, mutation_file_name);
+
         /// We release all locks except alter_intention_lock which allows
         /// to execute alter queries sequentially
         table_lock_holder.releaseAllExceptAlterIntention();
@@ -248,7 +253,7 @@ void StorageMergeTree::alter(
         /// Always execute required mutations synchronously, because alters
         /// should be executed in sequential order.
         if (!maybe_mutation_commands.empty())
-            mutateImpl(maybe_mutation_commands, /* mutations_sync = */ 1);
+            waitForMutation(mutation_version, mutation_file_name);
     }
 }
 
@@ -351,43 +356,42 @@ public:
 };
 
 
-void StorageMergeTree::mutateImpl(const MutationCommands & commands, size_t mutations_sync)
+Int64 StorageMergeTree::startMutation(const MutationCommands & commands, String & mutation_file_name)
 {
     /// Choose any disk, because when we load mutations we search them at each disk
     /// where storage can be placed. See loadMutations().
     auto disk = getStoragePolicy()->getAnyDisk();
-    String file_name;
     Int64 version;
-
-    {
     std::lock_guard lock(currently_processing_in_background_mutex);
 
     MergeTreeMutationEntry entry(commands, disk, relative_data_path, insert_increment.get());
     version = increment.get();
     entry.commit(version);
-        file_name = entry.file_name;
-        auto insertion = current_mutations_by_id.emplace(file_name, std::move(entry));
+    mutation_file_name = entry.file_name;
+    auto insertion = current_mutations_by_id.emplace(mutation_file_name, std::move(entry));
     current_mutations_by_version.emplace(version, insertion.first->second);
 
-        LOG_INFO(log, "Added mutation: " << file_name);
+    LOG_INFO(log, "Added mutation: " << mutation_file_name);
     merging_mutating_task_handle->wake();
-    }
+    return version;
+}
 
-    /// We have to wait mutation end
-    if (mutations_sync > 0)
-    {
+void StorageMergeTree::waitForMutation(Int64 version, const String & file_name)
+{
     LOG_INFO(log, "Waiting mutation: " << file_name);
     auto check = [version, this]() { return shutdown_called || isMutationDone(version); };
     std::unique_lock lock(mutation_wait_mutex);
     mutation_wait_event.wait(lock, check);
     LOG_INFO(log, "Mutation " << file_name << " done");
-    }
-
 }
 
 void StorageMergeTree::mutate(const MutationCommands & commands, const Context & query_context)
 {
-    mutateImpl(commands, query_context.getSettingsRef().mutations_sync);
+    String mutation_file_name;
+    Int64 version = startMutation(commands, mutation_file_name);
+
+    if (query_context.getSettingsRef().mutations_sync > 0)
+        waitForMutation(version, mutation_file_name);
 }
 
 namespace

dbms/Storages/StorageMergeTree.h

@@ -120,7 +120,11 @@ private:
 
     BackgroundProcessingPoolTaskResult movePartsTask();
 
-    void mutateImpl(const MutationCommands & commands, size_t mutations_sync);
+    /// Allocate block number for new mutation, write mutation to disk
+    /// and into in-memory structures. Wake up merge-mutation task.
+    Int64 startMutation(const MutationCommands & commands, String & mutation_file_name);
+    /// Wait until mutation with version will finish mutation for all parts
+    void waitForMutation(Int64 version, const String & filename);
 
     /// Try and find a single part to mutate and mutate it. If some part was successfully mutated, return true.
     bool tryMutatePart();