[MCOL-4709] Disk-based aggregation

* Introduce multigeneration aggregation

* Do not save unused part of RGDatas to disk
* Add IO error explanation (strerror)

* Reduce memory usage while aggregating
* introduce in-memory generations to better memory utilization

* Try to limit the qty of buckets at a low limit

* Refactor disk aggregation a bit
* pass calculated hash into RowAggregation
* try to keep some RGData with free space in memory

* do not dump more than half of rowgroups to disk if generations are
  allowed, instead start a new generation
* for each thread shift the first processed bucket at each iteration,
  so the generations start more evenly

* Unify temp data location

* Explicitly create temp subdirectories
  whether disk aggregation/join are enabled or not

utils/common/threadnaming.cpp

@@ -16,6 +16,7 @@
    MA 02110-1301, USA. */
 
 #include <sys/prctl.h>
+#include "threadnaming.h"
 
 namespace utils
 {
@@ -23,4 +24,11 @@ namespace utils
     {
         prctl(PR_SET_NAME, threadName, 0, 0, 0);
     }
+
+    std::string getThreadName()
+    {
+      char buf[32];
+      prctl(PR_GET_NAME, buf, 0, 0, 0);
+      return std::string(buf);
+    }
 } // end of namespace

utils/common/threadnaming.h

@@ -17,8 +17,11 @@
 #ifndef H_SETTHREADNAME
 #define H_SETTHREADNAME
 
+#include <string>
+
 namespace utils
 {
     void setThreadName(const char *threadName);
+    std::string getThreadName();
 } // end of namespace
 #endif