This commit drastically reduces the number of allocations needed to
deserialize a transaction and its scripts by using the combination of a
free list for initially deserializing the individual scripts along with
copying them into a single contiguous byte slice after the final size is
known and modifying each script in the transaction to point to its
location within the contiguous blob.
The end result is only a single allocation that holds all of the scripts
for a transaction regardless of the total number of scripts it has.
The script free list allows a maximum of 12,500 items with each buffer
being 512 bytes. This implies it will have a peak usage of 6.1MB. The
values were chosen based on profiling data and a desire to allow at
least 100 scripts per transaction to be simultaneously deserialized by
125 peers.
Also, while optimizing, decode directly into the existing previous
outpoint structure of each transaction input in order to avoid the extra
allocation per input that is otherwise caused when the local escapes to
the heap.
The following is a before and after comparison of the allocations
with the benchmarks that did not change removed:
benchmark old allocs new allocs delta
-----------------------------------------------------------
ReadTxOut 1 0 -100.00%
ReadTxIn 2 0 -100.00%
DeserializeTxSmall 7 5 -28.57%
DeserializeTxLarge 11146 6 -99.95%
The current code involves a ton of small allocations which is harsh on
the garbage collector and in turn causes a lot of addition runtime
overhead both in terms of additional memory and processing time.
In order to improve the situation, this drasticially reduces the number
of allocations by creating contiguous slices of objects and
deserializing into them. Since the final data structures consist of
slices of pointers to the objects, they are constructed by pointing them
into the appropriate offset of the contiguous slice.
This could be improved upon even further by converting all of the data
structures provided the wire package to be slices of contiguous objects
directly, however that would be a major breaking API change and would
end up requiring updating a lot more code in every caller. I do think
that ultimately the API should be changed, but the changes in this
commit already makes a massive difference and it doesn't require
touching any of the callers, so it is a good place to begin.
The following is a before and after comparison of the allocations
with the benchmarks that did not change removed:
benchmark old allocs new allocs delta
-----------------------------------------------------------
DeserializeTxLarge 16715 11146 -33.32%
DecodeGetHeaders 501 2 -99.60%
DecodeHeaders 2001 2 -99.90%
DecodeGetBlocks 501 2 -99.60%
DecodeAddr 3001 2002 -33.29%
DecodeInv 50003 3 -99.99%
DecodeNotFound 50002 3 -99.99%
DecodeMerkleBlock 107 3 -97.20%
This introduces a new binary free list which provides a concurrent safe
list of unused buffers for the purpose of serializing and deserializing
primitive integers to their raw binary bytes.
For convenience, the type also provides functions for each of the
primitive unsigned integers that automatically obtain a buffer from the
free list, perform the necessary binary conversion, read from or write
to the given io.Reader or io.Writer, and return the buffer to the free
list.
A global instance of the type has been introduced with a maximum number
of 1024 items. Since each buffer is 8 bytes, it will consume a maximum
of 8KB. Theoretically, this value would only allow up to 1024 peers
simultaneously reading and writing without having to resort to burdening
the garbage collector with additional allocations. However, due to the
fact the code is designed in such a way that the buffers are quickly
used and returned to the free list, in practice it can support much more
than 1024 peers without involving the garbage collector since it is
highly unlikely every peer would need a buffer at the exact same time.
The following is a before and after comparison of the allocations
with the benchmarks that did not change removed:
benchmark old allocs new allocs delta
-------------------------------------------------------------
WriteVarInt1 1 0 -100.00%
WriteVarInt3 1 0 -100.00%
WriteVarInt5 1 0 -100.00%
WriteVarInt9 1 0 -100.00%
ReadVarInt1 1 0 -100.00%
ReadVarInt3 1 0 -100.00%
ReadVarInt5 1 0 -100.00%
ReadVarInt9 1 0 -100.00%
ReadVarStr4 3 2 -33.33%
ReadVarStr10 3 2 -33.33%
WriteVarStr4 2 1 -50.00%
WriteVarStr10 2 1 -50.00%
ReadOutPoint 1 0 -100.00%
WriteOutPoint 1 0 -100.00%
ReadTxOut 3 1 -66.67%
WriteTxOut 2 0 -100.00%
ReadTxIn 5 2 -60.00%
WriteTxIn 3 0 -100.00%
DeserializeTxSmall 15 7 -53.33%
DeserializeTxLarge 33428 16715 -50.00%
SerializeTx 8 0 -100.00%
ReadBlockHeader 7 1 -85.71%
WriteBlockHeader 10 4 -60.00%
DecodeGetHeaders 1004 501 -50.10%
DecodeHeaders 18002 4001 -77.77%
DecodeGetBlocks 1004 501 -50.10%
DecodeAddr 9002 4001 -55.55%
DecodeInv 150005 50003 -66.67%
DecodeNotFound 150004 50002 -66.67%
DecodeMerkleBlock 222 108 -51.35%
TxSha 10 2 -80.00%
This commit removes the error returns from the BlockHeader.BlockSha,
MsgBlock.BlockSha, and MsgTx.TxSha functions since they can never fail and
end up causing a lot of unneeded error checking throughout the code base.
It also updates all call sites for the change.
This commit adds a new function which is similar to the DoubleSha256
function except it returns a ShaHash copy instead of a byte slice. It
also adds a new benchmark for it.
This can be a slight optimization in certain cases where the caller
ultimately wants a ShaHash since it can avoid a heap allocation and
additional copy to convert the result to a ShaHash (the function simply
performs a type cast against the returned array which is not possible
against a []byte).
existing: DoubleSha256 500000 3081 ns/op 32 B/op 1 allocs/op
new: DoubleSha256SH 500000 2939 ns/op 0 B/op 0 allocs/op
The hashing functions for blocks and transactions have also been updated
to make use of the new function since they directly return the ShaHash.
The transaction change in particular is quite useful since transactions
are frequently hashed and this change allows all of those hashes to avoid
an additional heap allocation.
This commit provides a new function named PkScriptLocs on the MsgTx type
which can be used to efficiently retrieve a list of offsets for the public
key scripts for the serialized form of the transaction.
This is useful for certain applications which store fully serialized
transactions and want to be able to quickly index into the serialized
transaction to extract a give public key script directly thereby avoiding
the need to deserialize the entire transaction.
This commit contains the entire btcwire repository along with several
changes needed to move all of the files into the wire directory in
order to prepare it for merging. This does NOT update btcd or any of the
other packages to use the new location as that will be done separately.
- All import paths in the old btcwire test files have been changed to the
new location
- All references to btcwire as the package name have been chagned to
wire
- The coveralls badge has been removed since it unfortunately doesn't
support coverage of sub-packages
This is ongoing work toward #214.
