Disable parallelize_output_from_storages for all system tables

Signed-off-by: Azat Khuzhin <a.khuzhin@semrush.com>

src/Storages/IStorage.h

@@ -376,10 +376,11 @@ private:
     /// even when the storage returned only one stream of data for reading?
     /// It is beneficial, for example, when you read from a file quickly,
     /// but then do heavy computations on returned blocks.
-    /// This is enabled by default, but in some cases shouldn't be done.
-    /// For example, when you read from system.numbers instead of system.numbers_mt,
-    /// you still expect the data to be processed sequentially.
-    virtual bool parallelizeOutputAfterReading(ContextPtr) const { return true; }
+    ///
+    /// This is enabled by default, but in some cases shouldn't be done (for
+    /// example it is disabled for all system tables, since it is pretty
+    /// useless).
+    virtual bool parallelizeOutputAfterReading(ContextPtr) const { return !isSystemStorage(); }
 
 public:
     /// Other version of read which adds reading step to query plan.

src/Storages/System/IStorageSystemOneBlock.h

@@ -61,8 +61,6 @@ public:
 
     bool isSystemStorage() const override { return true; }
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
     static NamesAndAliases getNamesAndAliases() { return {}; }
 };
 

src/Storages/System/StorageSystemDisks.h

@@ -30,8 +30,6 @@ public:
         size_t num_streams) override;
 
     bool isSystemStorage() const override { return true; }
-
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
 };
 
 }

src/Storages/System/StorageSystemNumbers.h

@@ -40,8 +40,6 @@ public:
         size_t max_block_size,
         size_t num_streams) override;
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
     bool hasEvenlyDistributedRead() const override { return true; }
     bool isSystemStorage() const override { return true; }
     bool supportsTransactions() const override { return true; }

src/Storages/System/StorageSystemOne.h

@@ -30,8 +30,6 @@ public:
         size_t max_block_size,
         size_t num_streams) override;
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
     bool isSystemStorage() const override { return true; }
 
     bool supportsTransactions() const override { return true; }

src/Storages/System/StorageSystemPartsBase.h

@@ -69,8 +69,6 @@ public:
 
     bool isSystemStorage() const override { return true; }
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
 private:
     static bool hasStateColumn(const Names & column_names, const StorageSnapshotPtr & storage_snapshot);
 

src/Storages/System/StorageSystemRemoteDataPaths.h

@@ -22,8 +22,6 @@ public:
         QueryProcessingStage::Enum processed_stage,
         size_t max_block_size,
         size_t num_streams) override;
-
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
 };
 
 }

src/Storages/System/StorageSystemReplicas.h

@@ -28,8 +28,6 @@ public:
         size_t num_streams) override;
 
     bool isSystemStorage() const override { return true; }
-
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
 };
 
 }

src/Storages/System/StorageSystemStackTrace.h

@@ -37,8 +37,6 @@ public:
 
     bool isSystemStorage() const override { return true; }
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
 protected:
     mutable std::mutex mutex;
     Poco::Logger * log;

src/Storages/System/StorageSystemStoragePolicies.h

@@ -30,8 +30,6 @@ public:
         size_t num_streams) override;
 
     bool isSystemStorage() const override { return true; }
-
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
 };
 
 }

src/Storages/System/StorageSystemZeros.h

@@ -31,8 +31,6 @@ public:
         size_t max_block_size,
         size_t num_streams) override;
 
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
-
     bool hasEvenlyDistributedRead() const override { return true; }
     bool isSystemStorage() const override { return true; }
     bool supportsTransactions() const override { return true; }

src/Storages/System/StorageSystemZooKeeper.h

@@ -35,7 +35,6 @@ public:
     bool isSystemStorage() const override { return true; }
     bool supportsIndexForIn() const override { return true; }
     bool mayBenefitFromIndexForIn(const ASTPtr & node, ContextPtr, const StorageMetadataPtr &) const override;
-    bool parallelizeOutputAfterReading(ContextPtr) const override { return false; }
 };
 
 }