RFR: 8320215: HeapDumper can use DumpWriter buffer during merge

[Yi Yang]

On Fri, 19 Apr 2024 00:10:12 GMT, Alex Menkov <amenkov at openjdk.org> wrote:

> The fix updates HeapMerger to use writer buffer (no need to copy memory, also writer buffer is 1MB instead of 4KB).
> Additionally fixed small issue in FileWriter (looks like `ssize_t` instead of `size_t` is a typo, the argument should be unsigned)
> 
> Testing: all HeapDump-related tests on Oracle supported platforms

I remember experimenting with different buffer sizes and figuring out that 4KB was the sweet spot. We could potentially switch to 1MB, but it would be better if we had some benchmark numbers to back that up.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/18850#issuecomment-2136422628