Elect compression dictionary once per multi chunk writer session in compaction

commit_hash:356b41fe9f7f12a3263082a94070464f588b650b

Author: akozhikhov

yt/yt/client/table_client/config.cpp

@@ -289,6 +289,10 @@ void TDictionaryCompressionConfig::Register(TRegistrar registrar)
         .Default(0.7)
         .InRange(0, 1);
 
+    registrar.Parameter("elect_random_policy", &TThis::ElectRandomPolicy)
+        .Default(false)
+        .DontSerializeDefault();
+
     registrar.Postprocessor([] (TThis* config) {
         if (config->DesiredSampleCount > config->MaxProcessedSampleCount) {
             THROW_ERROR_EXCEPTION("\"desired_sample_count\" cannot be greater than \"max_processed_sample_count\"");

yt/yt/client/table_client/config.h

@@ -251,6 +251,9 @@ struct TDictionaryCompressionConfig
     //! Upper limit on acceptable compression ratio. No chunk compression is performed if this limit is exceeded.
     double MaxAcceptableCompressionRatio;
 
+    //! For testing purposes only.
+    bool ElectRandomPolicy;
+
     REGISTER_YSON_STRUCT(TDictionaryCompressionConfig);
 
     static void Register(TRegistrar registrar);