Tutorial :Why can't I leverage 4GB of RAM in my computer to process less than 2GB of information in C#?


Scenario: over 1.5GB of text and csv files that I need to process mathematically. I tried using SQL Server Express, but loading the information, even with BULK import takes a very long time, and ideally I need to have the entire data set in memory, to reduce hard disk IO.

There are over 120,000,000 records, but even when I attempt to filter the information to just one column (in-memory), my C# console application is consuming ~3.5GB of memory to process just 125MB (700MB actually read-in) of text.

It seems that the references to the strings and string arrays are not being collected by the GC, even after setting all references to null and encapsulating IDisposables with the using keyword.

I think the culprit is the String.Split() method which is creating a new string for each comma separated value.

You may suggest that I shouldn't even read the unneeded* columns into a string array, but that misses the point: How can I place this entire data set in memory, so I can process it in parallel in C#?

I could optimize the statistical algorithms and coordinate tasks with a sophisticated scheduling algorithm, but this is something I was hoping to do before I ran into memory problems, and not because of.

I have included a full console application that simulates my environment and should help replicate the problem.

Any help is appreciated. Thanks in advance.

using System;  using System.Collections.Generic;  using System.Text;  using System.IO;    namespace InMemProcessingLeak  {      class Program      {          static void Main(string[] args)          {              //Setup Test Environment. Uncomment Once              //15000-20000 files would be more realistic              //InMemoryProcessingLeak.GenerateTestDirectoryFilesAndColumns(3000, 3);              //GC              GC.Collect();              //Demostrate Large Object Memory Allocation Problem (LOMAP)              InMemoryProcessingLeak.SelectColumnFromAllFiles(3000, 2);          }      }        class InMemoryProcessingLeak      {          public static List<string> SelectColumnFromAllFiles(int filesToSelect, int column)          {              List<string> allItems = new List<string>();              int fileCount = filesToSelect;              long fileSize, totalReadSize = 0;                for (int i = 1; i <= fileCount; i++)              {                  allItems.AddRange(SelectColumn(i, column, out fileSize));                  totalReadSize += fileSize;                  Console.Clear();                  Console.Out.WriteLine("Reading file {0:00000} of {1}", i, fileCount);                  Console.Out.WriteLine("Memory = {0}MB", GC.GetTotalMemory(false) / 1048576);                  Console.Out.WriteLine("Total Read = {0}MB", totalReadSize / 1048576);              }              Console.ReadLine();              return allItems;            }            //reads a csv file and returns the values for a selected column          private static List<string> SelectColumn(int fileNumber, int column, out long fileSize)          {              string fileIn;              FileInfo file = new FileInfo(string.Format(@"MemLeakTestFiles/File{0:00000}.txt", fileNumber));              fileSize = file.Length;              using (System.IO.FileStream fs = file.Open(FileMode.Open, FileAccess.Read, FileShare.Read))              {                  using (System.IO.StreamReader sr = new System.IO.StreamReader(fs))                  {                      fileIn = sr.ReadToEnd();                  }              }                string[] lineDelimiter = { "\n" };              string[] allLines = fileIn.Split(lineDelimiter, StringSplitOptions.None);                List<string> processedColumn = new List<string>();                string current;              for (int i = 0; i < allLines.Length - 1; i++)              {                  current = GetColumnFromProcessedRow(allLines[i], column);                  processedColumn.Add(current);              }                for (int i = 0; i < lineDelimiter.Length; i++) //GC              {                  lineDelimiter[i] = null;              }              lineDelimiter = null;                for (int i = 0; i < allLines.Length; i++) //GC              {                  allLines[i] = null;              }              allLines = null;              current = null;                return processedColumn;          }            //returns a row value from the selected comma separated string and column position          private static string GetColumnFromProcessedRow(string line, int columnPosition)          {              string[] entireRow = line.Split(",".ToCharArray());              string currentColumn = entireRow[columnPosition];              //GC              for (int i = 0; i < entireRow.Length; i++)              {                  entireRow[i] = null;              }              entireRow = null;              return currentColumn;          }            #region Generators          public static void GenerateTestDirectoryFilesAndColumns(int filesToGenerate, int columnsToGenerate)          {              DirectoryInfo dirInfo = new DirectoryInfo("MemLeakTestFiles");              if (!dirInfo.Exists)              {                  dirInfo.Create();              }              Random seed = new Random();                string[] columns = new string[columnsToGenerate];                StringBuilder sb = new StringBuilder();              for (int i = 1; i <= filesToGenerate; i++)              {                  int rows = seed.Next(10, 8000);                  for (int j = 0; j < rows; j++)                  {                      sb.Append(GenerateRow(seed, columnsToGenerate));                  }                  using (TextWriter tw = new StreamWriter(String.Format(@"{0}/File{1:00000}.txt", dirInfo, i)))                  {                      tw.Write(sb.ToString());                      tw.Flush();                  }                  sb.Remove(0, sb.Length);                  Console.Clear();                  Console.Out.WriteLine("Generating file {0:00000} of {1}", i, filesToGenerate);              }          }            private static string GenerateString(Random seed)          {              StringBuilder sb = new StringBuilder();              int characters = seed.Next(4, 12);              for (int i = 0; i < characters; i++)              {                  sb.Append(Convert.ToChar(Convert.ToInt32(Math.Floor(26 * seed.NextDouble() + 65))));              }              return sb.ToString();          }            private static string GenerateRow(Random seed, int columnsToGenerate)          {              StringBuilder sb = new StringBuilder();                sb.Append(seed.Next());              for (int i = 0; i < columnsToGenerate - 1; i++)              {                  sb.Append(",");                  sb.Append(GenerateString(seed));              }              sb.Append("\n");                return sb.ToString();          }          

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