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https://issues.apache.org/jira/browse/AVRO-220?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Scott Banachowski updated AVRO-220:
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Attachment: (was: AVRO-220.patch)
> Dynamic schema resolution from writer to reader
> -----------------------------------------------
>
> Key: AVRO-220
> URL: https://issues.apache.org/jira/browse/AVRO-220
> Project: Avro
> Issue Type: Improvement
> Components: c++
> Reporter: Scott Banachowski
> Attachments: AVRO-220.patch, AVRO-220.patch
>
>
> This introduces a new feature for C++, which enables data written by one
> schema to be read by a different schema.
> Before parse time, it examines the two schemas, and assembles a list of
> instructions on how to parse the data, and how to translate the parsed data
> to the expected schema (or skip it, as appropriate). The result of this
> operation is a sequence of instructions.
> At parse time, it basically follows the assembled list of instructions. The
> instructions can be created once, and then reused to read multiple messages
> (analogous to assembling a program that does the parsing, and then executing
> this program when you want to read the data).
> A structure is used when assembling the instructions, that holds a mapping of
> memory locations for primitives (relative to the start of some structure).
> This tells the parser where to copy the data to while parsing from the writer
> schema to a C++ structure. For non-primitive types, it stores the memory
> location for a functor that returns a destination address when invoked (for
> example, to add a map entry the functor will allocate the map entry, and
> return an address for the parser to write the actual data. Then the
> instruction for the map data type is invoked to populate this address).
> Setting up this offset structure is a chore, but using the code generator
> make it simple. The code generator correctly cranks out these structures for
> all the data types it generates.
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