Pre-allocate buffer (#422)

If we let transcode to its own allocation it will allocate a small
vector, start filling it, resize the vector, fill it some more, resize
the vector, etc.

Instead in this commit we pre-allocate a vector of the corect size and
pass it to transcode().

Inspired by #399

Author: JoaoAparicio

Project.toml

@@ -33,6 +33,7 @@ PooledArrays = "2dfb63ee-cc39-5dd5-95bd-886bf059d720"
 SentinelArrays = "91c51154-3ec4-41a3-a24f-3f23e20d615c"
 Tables = "bd369af6-aec1-5ad0-b16a-f7cc5008161c"
 TimeZones = "f269a46b-ccf7-5d73-abea-4c690281aa53"
+TranscodingStreams = "3bb67fe8-82b1-5028-8e26-92a6c54297fa"
 UUIDs = "cf7118a7-6976-5b1a-9a39-7adc72f591a4"
 WorkerUtilities = "76eceee3-57b5-4d4a-8e66-0e911cebbf60"
 
@@ -48,6 +49,7 @@ PooledArrays = "0.5, 1.0"
 SentinelArrays = "1"
 Tables = "1.1"
 TimeZones = "1"
+TranscodingStreams = "0.9.12"
 WorkerUtilities = "1.1"
 julia = "1.6"
 

src/table.jl

@@ -521,10 +521,11 @@ function uncompress(ptr::Ptr{UInt8}, buffer, compression)
     len = unsafe_load(convert(Ptr{Int64}, ptr))
     ptr += 8 # skip past uncompressed length as Int64
     encodedbytes = unsafe_wrap(Array, ptr, buffer.length - 8)
+    decodedbytes = Vector{UInt8}(undef, len)
     if compression.codec === Meta.CompressionTypes.LZ4_FRAME
-        decodedbytes = transcode(LZ4FrameDecompressor, encodedbytes)
+        transcode(LZ4FrameDecompressor, encodedbytes, decodedbytes)
     elseif compression.codec === Meta.CompressionTypes.ZSTD
-        decodedbytes = transcode(ZstdDecompressor, encodedbytes)
+        transcode(ZstdDecompressor, encodedbytes, decodedbytes)
     else
         error("unsupported compression type when reading arrow buffers: $(typeof(compression.codec))")
     end