Alternator request sizes can be up to 16 MB, but the current implementation
had the Seastar HTTP server read the entire request as a contiguous string,
and then processed it. We can't avoid reading the entire request up-front -
we want to verify its integrity before doing any additional processing on it.
But there is no reason why the entire request needs to be stored in one big
*contiguous* allocation. This always a bad idea. We should use a non-
contiguous buffer, and that's the goal of this patch.
We use a new Seastar HTTPD feature where we can ask for an input stream,
instead of a string, for the request's body. We then begin the request
handling by reading lthe content of this stream into a
vector<temporary_buffer<char>> (which we alias "chunked_content"). We then
use this non-contiguous buffer to verify the request's signature and
if successful - parse the request JSON and finally execute it.
Beyond avoiding contiguous allocations, another benefit of this patch is
that while parsing a long request composed of chunks, we free each chunk
as soon as its parsing completed. This reduces the peak amount of memory
used by the query - we no longer need to store both unparsed and parsed
versions of the request at the same time.
Although we already had tests with requests of different lengths, most
of them were short enough to only have one chunk, and only a few had
2 or 3 chunks. So we also add a test which makes a much longer request
(a BatchWriteItem with large items), which in my experiment had 17 chunks.
The goal of this test is to verify that the new signature and JSON parsing
code which needs to cross chunk boundaries work as expected.
Fixes#7213.
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <20210309222525.1628234-1-nyh@scylladb.com>
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