zeroshade commented on code in PR #35769:
URL: https://github.com/apache/arrow/pull/35769#discussion_r1207041723
##########
go/arrow/datatype_binary.go:
##########
@@ -83,16 +93,168 @@ func (t *LargeStringType) Layout() DataTypeLayout {
func (t *LargeStringType) OffsetTypeTraits() OffsetTraits { return Int64Traits
}
func (LargeStringType) IsUtf8() bool { return true }
+const (
+ StringHeaderPrefixLen = 4
+ stringHeaderInlineSize = 12
+)
+
+func IsStringHeaderInline(length int) bool {
+ return length < stringHeaderInlineSize
+}
+
+// StringHeader is a variable length string (utf8) or byte slice with
+// a 4 byte prefix and inline optimization for small values (12 bytes
+// or fewer). This is similar to Go's standard string but limited by
+// a length of Uint32Max and up to the first four bytes of the string
+// are copied into the struct. This prefix allows failing comparisons
+// early and can reduce CPU cache working set when dealing with short
+// strings.
+//
+// There are two situations:
+//
+// Short string |----|----|--------|
+// ^ ^ ^
+// | | |
+// size prefix remaining in-line portion, zero padded
+//
+// IO Long String |----|----|----|----|
+// ^ ^ ^ ^
+// | | | |
+// size prefix buffer index and offset to out-of-line portion
+//
+// Adapted from TU Munich's UmbraDB [1], Velox, DuckDB.
+//
+// [1]: https://db.in.tum.de/~freitag/papers/p29-neumann-cidr20.pdf
+type StringHeader struct {
+ size uint32
+ // the first 4 bytes of this are the prefix for the string
+ // if size <= StringHeaderInlineSize, then the entire string
+ // is in the data array and is zero padded.
+ // if size > StringHeaderInlineSize, the next 8 bytes are 2 uint32
+ // values which are the buffer index and offset in that buffer
+ // containing the full string.
+ data [stringHeaderInlineSize]byte
+}
+
+func (sh *StringHeader) IsInline() bool {
+ return sh.size <= uint32(stringHeaderInlineSize)
+}
+
+func (sh *StringHeader) Len() int { return int(sh.size) }
+func (sh *StringHeader) Prefix() [StringHeaderPrefixLen]byte {
+ return *(*[4]byte)(unsafe.Pointer(&sh.data))
+}
+
+func (sh *StringHeader) BufferIndex() uint32 {
+ return endian.Native.Uint32(sh.data[StringHeaderPrefixLen:])
+}
+
+func (sh *StringHeader) BufferOffset() uint32 {
+ return endian.Native.Uint32(sh.data[StringHeaderPrefixLen+4:])
+}
+
+func (sh *StringHeader) InlineBytes() (data []byte) {
+ debug.Assert(sh.IsInline(), "calling InlineBytes on non-inline
StringHeader")
+ return sh.data[:sh.size]
+}
+
+func (sh *StringHeader) InlineData() (data string) {
+ debug.Assert(sh.IsInline(), "calling InlineData on non-inline
StringHeader")
+ h := (*reflect.StringHeader)(unsafe.Pointer(&data))
+ h.Data = uintptr(unsafe.Pointer(&sh.data))
+ h.Len = int(sh.size)
+ return
+}
+
+func (sh *StringHeader) SetBytes(data []byte) int {
+ sh.size = uint32(len(data))
+ if sh.IsInline() {
+ return copy(sh.data[:], data)
+ }
+ return copy(sh.data[:4], data)
+}
+
+func (sh *StringHeader) SetString(data string) int {
+ sh.size = uint32(len(data))
+ if sh.IsInline() {
+ return copy(sh.data[:], data)
+ }
+ return copy(sh.data[:4], data)
+}
+
+func (sh *StringHeader) SetIndexOffset(bufferIndex, offset uint32) {
+ endian.Native.PutUint32(sh.data[StringHeaderPrefixLen:], bufferIndex)
+ endian.Native.PutUint32(sh.data[StringHeaderPrefixLen+4:], offset)
+}
+
+func (sh *StringHeader) Equals(buffers []*memory.Buffer, other *StringHeader,
otherBuffers []*memory.Buffer) bool {
+ if sh.sizeAndPrefixAsInt() != other.sizeAndPrefixAsInt() {
+ return false
+ }
+
+ if sh.IsInline() {
+ return sh.inlinedAsInt64() == other.inlinedAsInt64()
+ }
+
+ data := buffers[sh.BufferIndex()].Bytes()[sh.BufferOffset() :
sh.BufferOffset()+sh.size]
+ otherData :=
otherBuffers[other.BufferIndex()].Bytes()[other.BufferOffset() :
other.BufferOffset()+other.size]
+ return bytes.Equal(data, otherData)
+}
+
+func (sh *StringHeader) inlinedAsInt64() int64 {
+ s := unsafe.Slice((*int64)(unsafe.Pointer(sh)), 2)
+ return s[1]
+}
+
+func (sh *StringHeader) sizeAndPrefixAsInt() int64 {
+ s := unsafe.Slice((*int64)(unsafe.Pointer(sh)), 2)
+ return s[0]
+}
+
+type BinaryViewType struct{}
+
+func (*BinaryViewType) ID() Type { return BINARY_VIEW }
+func (*BinaryViewType) Name() string { return "binary_view" }
+func (*BinaryViewType) String() string { return "binary_view" }
+func (*BinaryViewType) IsUtf8() bool { return false }
+func (*BinaryViewType) binary() {}
+func (*BinaryViewType) view() {}
Review Comment:
convenience interfaces. in `datatype.go` there's `BinaryDataType` which
defines an interface adding `IsUtf8() bool` which requires a `binary()` method
so that you can easily write code that works for *all* of these binary
interfaces via type switches or interfaces.
Then I added this `view()` method for a `BinaryViewDataType` so you can
write code targeting both BinaryView and StringView without needing to
duplicate code by just using the interface in the type switch.
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