public bool TryCompression(Table table, TableSchema schema)
{
try
{
var tx = table._tx;
int maxSpace = ZstdLib.GetMaxCompression(RawBuffer.Length);
_compressedScope = tx.Allocator.Allocate(maxSpace + OverheadSize, out CompressedBuffer);
Compressed = false;
var compressionDictionary = tx.LowLevelTransaction.Environment.CompressionDictionariesHolder
.GetCompressionDictionaryFor(tx, table.CurrentCompressionDictionaryId);
CompressionTried = true;
var size = ZstdLib.Compress(RawBuffer.ToReadOnlySpan(), CompressedBuffer.ToSpan(), compressionDictionary);
size += WriteVariableSizeIntInReverse(CompressedBuffer.Ptr + size, compressionDictionary.Id);
CompressedBuffer.Truncate(size);
var compressionRatio = GetCompressionRatio(size, RawBuffer.Length);
if (compressionRatio > compressionDictionary.ExpectedCompressionRatio + 10)
{
// training dictionaries is expensive, only do that if we see that the current compressed
// value is significantly worse than the previous one
var etagTree = table.GetFixedSizeTree(schema.CompressedEtagSourceIndex);
if (ShouldRetrain(etagTree))
{
MaybeTrainCompressionDictionary(table, etagTree);
}
}
if (CompressedBuffer.Length >= RawBuffer.Length)
{
// we compressed too large, so we skip compression here
_compressedScope.Dispose();
// Explicitly not disposing this, we need to have the raw buffer
// when we do update then insert and the size is too large
// RawScope.Dispose();
Compressed = false;
return(false);
}
Compressed = true;
return(true);
}
catch
{
_compressedScope.Dispose();
RawScope.Dispose();
throw;
}
}
