Test file to see why Esent takes big files

Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using Microsoft.Isam.Esent.Interop;

namespace EsentSize
{
	class Program
	{
		static void Main()
		{
			var database = "test";
			if (Directory.Exists(database))
				Directory.Delete(database, true);

			SystemParameters.MaxInstances = 1024;
			CreateDatabase(database);

			ReportDatabaseSize(database);

			WriteDocuments(database);

			ReportDatabaseSize(database);

		}

		private static void WriteDocuments(string database)
		{
			JET_INSTANCE instance = JET_INSTANCE.Nil;
			try
			{
				Configure(database, instance);
				Api.JetCreateInstance(out instance, database + Guid.NewGuid());
				Api.JetInit(ref instance);
				using (var session = new Session(instance))
				{
					JET_DBID dbid;
					Api.JetAttachDatabase(session, Path.Combine(database, "database"), AttachDatabaseGrbit.None);
					Api.JetOpenDatabase(session, Path.Combine(database, "database"), null, out dbid, OpenDatabaseGrbit.None);

					using (var tx = new Transaction(session))
					using (var documents = new Table(session, dbid, "documents", OpenTableGrbit.None))
					{
						var documentsColumns = Api.GetColumnDictionary(session, documents);
						for (int i = 0; i < 1024; i++)
						{
							using (var update = new Update(session, documents, JET_prep.Insert))
							{
								Api.SetColumn(session, documents, documentsColumns["key"], "tests/" + i, Encoding.Unicode);
								using (Stream stream = new BufferedStream(new ColumnStream(session, documents, documentsColumns["data"])))
								{
									stream.Write(new byte[1024], 0, 1024);
									stream.Flush();
								}

								Api.SetColumn(session, documents, documentsColumns["etag"], Guid.NewGuid().ToByteArray());
								Api.SetColumn(session, documents, documentsColumns["last_modified"], DateTime.UtcNow);

								using (Stream stream = new BufferedStream(new ColumnStream(session, documents, documentsColumns["metadata"])))
								{
									stream.Write(new byte[128], 0, 128);
									stream.Flush();
								}

								update.Save();
							}
						}
						tx.Commit(CommitTransactionGrbit.None);
					}

					Api.JetCloseDatabase(session, dbid, CloseDatabaseGrbit.None);
				}
			}
			finally
			{
				Api.JetTerm2(instance, TermGrbit.Complete);
			}
		}

		private static void ReportDatabaseSize(string database)
		{
			JET_INSTANCE instance = JET_INSTANCE.Nil;
			try
			{
				Configure(database, instance);
				Api.JetCreateInstance(out instance, database + Guid.NewGuid());
				Api.JetInit(ref instance);
				using (var session = new Session(instance))
				{
					JET_DBID dbid;
					Api.JetAttachDatabase(session, Path.Combine(database, "database"), AttachDatabaseGrbit.None);
					Api.JetOpenDatabase(session, Path.Combine(database, "database"), null, out dbid, OpenDatabaseGrbit.None);

					int value;
					Api.JetGetDatabaseInfo(session, dbid, out value, JET_DbInfo.Filesize);

					Console.WriteLine("File size is {0:#,#} kb", (value*SystemParameters.DatabasePageSize)/1024);

					Api.JetCloseDatabase(session, dbid, CloseDatabaseGrbit.None);
				}
			}
			finally
			{
				Api.JetTerm2(instance, TermGrbit.Complete);
			}
		}

		private static void CreateDatabase(string database)
		{
			JET_INSTANCE instance = JET_INSTANCE.Nil;
			try
			{
				Configure(database,instance);
				Api.JetCreateInstance(out instance, database + Guid.NewGuid());
				Api.JetInit(ref instance);
				using (var session = new Session(instance))
				{
					JET_DBID dbid;
					Api.JetCreateDatabase(session, Path.Combine(database, "database"), null, out dbid, CreateDatabaseGrbit.None);

					CreateDocumentsTable(session, dbid);
					Api.JetCloseDatabase(session, dbid, CloseDatabaseGrbit.None);
				}
			}
			finally
			{
				Api.JetTerm2(instance, TermGrbit.Complete);
			}
		}

		private static void Configure(string path, JET_INSTANCE jetInstance)
		{
			new InstanceParameters(jetInstance)
			{
				CircularLog = true,
				Recovery = true,
				NoInformationEvent = false,
				CreatePathIfNotExist = true,
				TempDirectory = Path.Combine(path, "temp"),
				SystemDirectory = Path.Combine(path, "system"),
				LogFileDirectory = Path.Combine(path, "logs"),
				MaxVerPages = 128 * SystemParameters.DatabasePageSize,
				BaseName = "RVN",
				EventSource = "Raven",
				LogBuffers = 2048,
				LogFileSize = 4098,
				MaxSessions = 256,
				MaxCursors = 2048,
				DbExtensionSize = 4098,
				AlternateDatabaseRecoveryDirectory = path
			};
		}

		private static void CreateDocumentsTable(JET_SESID session, JET_DBID dbid)
		{
			JET_TABLEID tableid;
			Api.JetCreateTable(session, dbid, "documents", 1, 80, out tableid);
			JET_COLUMNID columnid;

			Api.JetAddColumn(session, tableid, "id", new JET_COLUMNDEF
			{
				coltyp = JET_coltyp.Long,
				grbit = ColumndefGrbit.ColumnFixed | ColumndefGrbit.ColumnAutoincrement | ColumndefGrbit.ColumnNotNULL
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "key", new JET_COLUMNDEF
			{
				cbMax = 255,
				coltyp = JET_coltyp.Text,
				cp = JET_CP.Unicode,
				grbit = ColumndefGrbit.ColumnTagged
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "etag", new JET_COLUMNDEF
			{
				cbMax = 16,
				coltyp = JET_coltyp.Binary,
				grbit = ColumndefGrbit.ColumnFixed | ColumndefGrbit.ColumnNotNULL,
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "last_modified", new JET_COLUMNDEF
			{
				coltyp = JET_coltyp.DateTime,
				grbit = ColumndefGrbit.ColumnFixed | ColumndefGrbit.ColumnNotNULL,
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "locked_by_transaction", new JET_COLUMNDEF
			{
				cbMax = 16,
				coltyp = JET_coltyp.Binary,
				grbit = ColumndefGrbit.ColumnTagged,
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "data", new JET_COLUMNDEF
			{
				coltyp = JET_coltyp.LongBinary,
				grbit = ColumndefGrbit.ColumnTagged
			}, null, 0, out columnid);

			Api.JetAddColumn(session, tableid, "metadata", new JET_COLUMNDEF
			{
				coltyp = JET_coltyp.LongBinary,
				grbit = ColumndefGrbit.ColumnTagged
			}, null, 0, out columnid);


			var indexDef = "+key\0\0";
			Api.JetCreateIndex(session, tableid, "by_key", CreateIndexGrbit.IndexDisallowNull | CreateIndexGrbit.IndexUnique, indexDef, indexDef.Length,
							   80);

			indexDef = "+id\0\0";
			Api.JetCreateIndex(session, tableid, "by_id", CreateIndexGrbit.IndexPrimary, indexDef, indexDef.Length,
							   80);

			indexDef = "+etag\0\0";
			Api.JetCreateIndex(session, tableid, "by_etag", CreateIndexGrbit.IndexDisallowNull, indexDef, indexDef.Length,
							   80);
		}
	}
}