Row compression using CLR and GZIP

Question

I want to compress a large table containing historical data that is rarely or not read at all. At first I try to use the built-in compressions ( row , page , column stored , column-stored archive ), but none of them can compress values ​​outside the line ( varchar(max) , nvarchar(max) ) and finally, I try to use the CLR solution.

SQL Server Compressed Row Set Solution Compresses the entire row set returned by this query using a custom CLR type.

For example:

 CREATE TABLE Archive ( [Date] DATETIME2 DEFAULT(GETUTCDATE()) ,[Data] [dbo].[CompressedRowset] ) INSERT INTO Archive([Data]) SELECT [dbo].[CompressQueryResults]('SELECT * FROM [dbo].[A]') 

It works, but I met the following problems:

• when I try to compress a large set of result lines, I get the following error :

  Msg 0, level 11, state 0, line 0 Severe error on the current command. Results, if any, should be discarded.

  In addition, the following statement works:

   SELECT [dbo].[CompressQueryResults] ('SELECT * FROM [dbo].[LargeA]') 

  but they are not:

   INSERT INTO Archive SELECT [dbo].[CompressQueryResults] ('SELECT * FROM [dbo].[LargeA]' DECLARE @A [dbo].[CompressedRowset] SELECT @A = [dbo].[CompressQueryResults] ('SELECT * FROM [dbo].[LargeA]') 

• to compress a rowset, t-sql type must be mapped to .net type ; Unfortunately, this does not apply to all types of sql - Displaying CLR parameter data ; I have already expanded the following function to handle more types , but how to handle types like geography , for example :

   static SqlDbType ToSqlType(Type t){ if (t == typeof(int)){ return SqlDbType.Int; } ... if (t == typeof(Byte[])){ return SqlDbType.VarBinary; } else { throw new NotImplementedException("CLR Type " + t.Name + " Not supported for conversion"); } } 

Here is the whole .net code:

 using System; using System.Data; using System.Data.SqlClient; using System.Data.SqlTypes; using Microsoft.SqlServer.Server; using System.IO; using System.Runtime.Serialization.Formatters.Binary; using System.IO.Compression; using System.Xml.Serialization; using System.Xml; [Serializable] [Microsoft.SqlServer.Server.SqlUserDefinedType ( Format.UserDefined ,IsByteOrdered = false ,IsFixedLength = false ,MaxByteSize = -1 ) ] public struct CompressedRowset : INullable, IBinarySerialize, IXmlSerializable { DataTable rowset; public DataTable Data { get { return this.rowset; } set { this.rowset = value; } } public override string ToString() { using (var sw = new StringWriter()) using (var xw = new XmlTextWriter(sw)) { WriteXml(xw); xw.Flush(); sw.Flush(); return sw.ToString(); } } public bool IsNull { get { return (this.rowset == null);} } public static CompressedRowset Null { get { CompressedRowset h = new CompressedRowset(); return h; } } public static CompressedRowset Parse(SqlString s) { using (var sr = new StringReader(s.Value)) using (var xr = new XmlTextReader(sr)) { var c = new CompressedRowset(); c.ReadXml(xr); return c; } } #region "Stream Wrappers" abstract class WrapperStream : Stream { public override bool CanSeek { get { return false; } } public override bool CanWrite { get { return false; } } public override void Flush() { } public override long Length { get { throw new NotImplementedException(); } } public override long Position { get { throw new NotImplementedException(); } set { throw new NotImplementedException(); } } public override long Seek(long offset, SeekOrigin origin) { throw new NotImplementedException(); } public override void SetLength(long value) { throw new NotImplementedException(); } } class BinaryWriterStream : WrapperStream { BinaryWriter br; public BinaryWriterStream(BinaryWriter br) { this.br = br; } public override bool CanRead { get { return false; } } public override bool CanWrite { get { return true; } } public override int Read(byte[] buffer, int offset, int count) { throw new NotImplementedException(); } public override void Write(byte[] buffer, int offset, int count) { br.Write(buffer, offset, count); } } class BinaryReaderStream : WrapperStream { BinaryReader br; public BinaryReaderStream(BinaryReader br) { this.br = br; } public override bool CanRead { get { return true; } } public override bool CanWrite { get { return false; } } public override int Read(byte[] buffer, int offset, int count) { return br.Read(buffer, offset, count); } public override void Write(byte[] buffer, int offset, int count) { throw new NotImplementedException(); } } #endregion #region "IBinarySerialize" public void Read(System.IO.BinaryReader r) { using (var rs = new BinaryReaderStream(r)) using (var cs = new GZipStream(rs, CompressionMode.Decompress)) { var ser = new BinaryFormatter(); this.rowset = (DataTable)ser.Deserialize(cs); } } public void Write(System.IO.BinaryWriter w) { if (this.IsNull) return; rowset.RemotingFormat = SerializationFormat.Binary; var ser = new BinaryFormatter(); using (var binaryWriterStream = new BinaryWriterStream(w)) using (var compressionStream = new GZipStream(binaryWriterStream, CompressionMode.Compress)) { ser.Serialize(compressionStream, rowset); } } #endregion /// <summary> /// This procedure takes an arbitrary query, runs it and compresses the results into a varbinary(max) blob. /// If the query has a large result set, then this procedure will use a large amount of memory to buffer the results in /// a DataTable, and more to copy it into a compressed buffer to return. /// </summary> /// <param name="query"></param> /// <param name="results"></param> //[Microsoft.SqlServer.Server.SqlProcedure] [SqlFunction(DataAccess = DataAccessKind.Read, SystemDataAccess = SystemDataAccessKind.Read, IsDeterministic = false, IsPrecise = false)] public static CompressedRowset CompressQueryResults(string query) { //open a context connection using (var con = new SqlConnection("Context Connection=true")) { con.Open(); var cmd = new SqlCommand(query, con); var dt = new DataTable(); using (var rdr = cmd.ExecuteReader()) { dt.Load(rdr); } //configure the DataTable for binary serialization dt.RemotingFormat = SerializationFormat.Binary; var bf = new BinaryFormatter(); var cdt = new CompressedRowset(); cdt.rowset = dt; return cdt; } } /// <summary> /// partial Type mapping between SQL and .NET /// </summary> /// <param name="t"></param> /// <returns></returns> static SqlDbType ToSqlType(Type t) { if (t == typeof(int)) { return SqlDbType.Int; } if (t == typeof(string)) { return SqlDbType.NVarChar; } if (t == typeof(Boolean)) { return SqlDbType.Bit; } if (t == typeof(decimal)) { return SqlDbType.Decimal; } if (t == typeof(float)) { return SqlDbType.Real; } if (t == typeof(double)) { return SqlDbType.Float; } if (t == typeof(DateTime)) { return SqlDbType.DateTime; } if (t == typeof(Int64)) { return SqlDbType.BigInt; } if (t == typeof(Int16)) { return SqlDbType.SmallInt; } if (t == typeof(byte)) { return SqlDbType.TinyInt; } if ( t == typeof(Guid)) { return SqlDbType.UniqueIdentifier; } //!!!!!!!!!!!!!!!!!!! if (t == typeof(Byte[])) { return SqlDbType.VarBinary; } else { throw new NotImplementedException("CLR Type " + t.Name + " Not supported for conversion"); } } /// <summary> /// This stored procedure takes a compressed DataTable and returns it as a resultset to the clinet /// or into a table using exec .... into ... /// </summary> /// <param name="results"></param> [Microsoft.SqlServer.Server.SqlProcedure] public static void UnCompressRowset(CompressedRowset results) { if (results.IsNull) return; DataTable dt = results.rowset; var fields = new SqlMetaData[dt.Columns.Count]; for (int i = 0; i < dt.Columns.Count; i++) { var col = dt.Columns[i]; var sqlType = ToSqlType(col.DataType); var colName = col.ColumnName; if (sqlType == SqlDbType.NVarChar || sqlType == SqlDbType.VarBinary) { fields[i] = new SqlMetaData(colName, sqlType, col.MaxLength); } else { fields[i] = new SqlMetaData(colName, sqlType); } } var record = new SqlDataRecord(fields); SqlContext.Pipe.SendResultsStart(record); foreach (DataRow row in dt.Rows) { record.SetValues(row.ItemArray); SqlContext.Pipe.SendResultsRow(record); } SqlContext.Pipe.SendResultsEnd(); } public System.Xml.Schema.XmlSchema GetSchema() { return null; } public void ReadXml(System.Xml.XmlReader reader) { if (rowset != null) { throw new InvalidOperationException("rowset already read"); } var ser = new XmlSerializer(typeof(DataTable)); rowset = (DataTable)ser.Deserialize(reader); } public void WriteXml(System.Xml.XmlWriter writer) { if (String.IsNullOrEmpty(rowset.TableName)) rowset.TableName = "Rows"; var ser = new XmlSerializer(typeof(DataTable)); ser.Serialize(writer, rowset); } } 

and here is the creation of the SQL objects:

 CREATE TYPE [dbo].[CompressedRowset] EXTERNAL NAME [CompressedRowset].[CompressedRowset]; GO CREATE FUNCTION [dbo].[CompressQueryResults] (@query [nvarchar](4000)) RETURNS [dbo].[CompressedRowset] AS EXTERNAL NAME [CompressedRowset].[CompressedRowset].[CompressQueryResults]; GO CREATE PROCEDURE [dbo].[UnCompressRowset] @results [dbo].[CompressedRowset] AS EXTERNAL NAME [CompressedRowset].[CompressedRowset].[UnCompressRowset]; GO 

Answer 1

It may be too late for the original question, but it may be worth considering that others are stumbling: SQL Server 2016 has compression and decompression functions (see here and here ) that can be useful here if the data you are trying to archive , contain large values ​​in the [N]VARCHAR and VARBINARY columns.

You will need to bake it at your business logic level or create some arrangement in SQL Server whereby you replicate your uncompressed table as a view to the support table (where the compressed values ​​are) and you get uncompressed data through DECOMPRESS and having INSTEAD OF triggers that update the support table (so that the view behaves like the original table for select / insert / update / delete, except for performance differences). A bit hacked, but it will work ...

For older versions of SQL, you can probably write a CLR function to complete the task.

This method, obviously, will not work for data sets consisting of small fields, of course, this compression style simply will not achieve anything on small values ​​(in fact, this will make them larger).

Answer 2

Instead, you decided to create a new Archive database (possibly configured for a simple recovery model), where do you dump all your old data? They can be easily accessed in queries, so no pain there, for example.

 SELECT * FROM archive..olddata 

When you create a db, place it on another disk and process it differently in your backup procedure - perhaps you perform the backup procedure once a week, and then after that you just need to substitute the backup - and after you crush it it is almost zero with 7zip / rar.

Do not try to compress db using NTFS compression, although the SQL server does not support it - I found out that I was very late in the evening :)