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* [PATCH] doc/design.txt: add a few more notes on compromises
@ 2015-01-15  7:49 Eric Wong
  0 siblings, 0 replies; only message in thread
From: Eric Wong @ 2015-01-15  7:49 UTC (permalink / raw)
  To: cmogstored-public

In case I forget, writing this down while my mind is on
the subject for other projects.
 doc/design.txt | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/doc/design.txt b/doc/design.txt
index f873834..495e1bf 100644
--- a/doc/design.txt
+++ b/doc/design.txt
@@ -1,4 +1,3 @@
 object relationships
@@ -26,3 +25,35 @@ mog_cfg[0] -- mog_svc[0] --- mog_mgmt[N]
 mog_cfg[1] -- mog_svc[1] --- mog_mgmt[M]
                          \-- mog_http[M]
+memory management
+cmogstored avoids dynamic memory allocation in common cases.
+Each file descriptor is mapped to a 128-byte (on 64-bit systems)
+slot of memory which maps all the critical data needed for most
+connections.  See fdmap.c for details.
+Userspace socket read buffers are per-thread in the common case (rather
+than per-client), as most request buffers do not need to live longer
+than a single event loop step (iteration).
+performance compromises
+We still use snprintf to generate HTTP response headers, and we use
+Ragel-generated code for the HTTP parser.  These choices were made for
+maintainability and readability rather than performance.
+Even with these performance compromises, cmogstored performance is
+expected to be competitive in the best-case (hot cache[1]) scenarios
+with other HTTP servers.
+Where cmogstored (and the original Perl mogstored) shines is in avoiding
+pathological head-of-line blocking when serving files from multiple
+mountpounts.  See queues.txt for more on the unique queue design for
+to take advantage of multiple cores and disks.
+[1] cmogstored does not do any caching on its own, it relies on the
+    operating system kernel.

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