Steve Lawrence created DAFFODIL-2851:
----------------------------------------
Summary: Excessive alloations in StringOfSpecifiedLengthMixin
Key: DAFFODIL-2851
URL: https://issues.apache.org/jira/browse/DAFFODIL-2851
Project: Daffodil
Issue Type: Bug
Components: Back End
Reporter: Steve Lawrence
The StringOfSpecifiedLengthMixin passes in the value of the
"maximumSimpleElementSizeInCharacters" tunable to the getSomeString function:
https://github.com/apache/daffodil/blob/main/daffodil-runtime1/src/main/scala/org/apache/daffodil/runtime1/processors/parsers/StringLengthParsers.scala#L89-L94
The getSomeString function calls withLocalCharBuffer which allocates a char
buffer of that size where it will decode the string. Currently, the tunable
defaults to 1MB. This size is pretty large, large enough to be a noticeable
contributor to allocations and cpu usage when profiling.
Fortunately, the allocated char buffer is cached and reused during the parse
(though each parse allocates a new one), so it's only a one time penalty per
parse. But most files are not going to have single strings nearly that large so
this large allocation is just a waste.
We should consider ways to reduce this allocation. Maybe simply decrease the
tunable? Or maybe change the logic so StringOfSpecifiedLength allocates a much
smaller amount, and grows the buffer if needed, maybe taking into account
bitLimit? Or maybe the buffer is shared among different parses in a
ThreadLocal, so we still allocate a large buffer, but the penalty is only once
per thread instead of once per parse? Likely other options...
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
