[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/configcpp/configcpp.cpp

@@ -59,6 +59,9 @@ namespace fs = boost::filesystem;
 #include "installdir.h"
 #ifdef _MSC_VER
 #include "idbregistry.h"
+#include <unordered_map>
+#else
+#include <tr1/unordered_map>
 #endif
 
 #include "bytestream.h"
@@ -673,6 +676,24 @@ const vector<string> Config::enumSection(const string& section)
 
     return fParser.enumSection(fDoc, section);
 }
+std::string Config::getTempFileDir(Config::TempDirPurpose what)
+{
+  std::string prefix = getConfig("SystemConfig", "SystemTempFileDir");
+  if (prefix.empty())
+  {
+    prefix.assign("/tmp/columnstore_tmp_files");
+  }
+  prefix.append("/");
+  switch (what)
+  {
+  case TempDirPurpose::Joins:
+    return prefix.append("joins/");
+  case TempDirPurpose::Aggregates:
+    return prefix.append("aggregates/");
+  }
+  // NOTREACHED
+  return {};
+}
 
 } //namespace config
 // vim:ts=4 sw=4: