![]() ![]() Hiding data and funneling it through narrow pipes prevents saturation of the hardware, and only much smarter JIT compilation (better inlining, better at spotting and rewriting idioms) could compensate for this. Ultimately, we have APIs like this in Java because people (rightly) don’t want to copy data, but the language lacks const semantics. This seems like such a narrow conduit to pipe data through, and maximum efficiency is precluded by abstraction here. */ ByteProcessor FIND_LF = new IndexOfProcessor ( LINE_FEED ) 1 UTF-8 is capable of encoding all 1,112,064 a valid Unicode code points using one to four one- byte (8-bit) code units. Defined by the Unicode Standard, the name is derived from Unicode Transformation Format 8-bit. Here’s what this looks like in the MongoDB Java public String readCString () /** UTF-8 is a variable-length character encoding standard used for electronic communication. This means that extracting the name is linear in its length, rather than constant time. To save space, attribute names in BSON are null terminated, at the cost of one byte, rather than length-prefixed which would cost four. ![]() ![]() To write a BSON parser, you just need a jump table associating each value type with a parser.Īs you scan the input, you read the type byte, read the attribute name, then look up and invoke the parser for the current type.įlexibility comes at a price: the attribute names in documents represent significant overhead compared to relational database tuples. Finding Null Terminators without BranchesīSON has a very simple structure: except at the very top level, it is a list of triplets consisting of a type byte, a name, and a (recursively defined) BSON value.I compare the most obvious, but branchy, implementation with a branch-free implementation, and use the Vector API in Project Panama to improve performance. HTTP 1.1 headers are delimited by CRLF sequences ĬBOR arrays are terminated by the stop character 0xFF. While this problem is simple, it has many applications in parsing: This post considers the benefits of branch-free algorithms through the lens of a trivial problem: finding the first position of a byte within an array. Thanks to everybody who reviewed and made helpful suggestions to improve this post. ![]()
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