* Item structure was changed to work with slab, where its last field
is used to access key, value, and ascii prefix, respectively.
* Item structured was worked to have a smaller footprint. It was
reduced from 104 bytes to 72 bytes.
* Reclaimer was temporarily disabled.
* Global LRU was removed from the cache. Now LRU eviction is done
on a per-slab-class basis, whenever the slab allocator runs out of
slab pages.
* Fragmentation issue is naturally solved with the slab algorithm,
where slab classes have chunks of the same size.
Expiration time is a 32-bit value as specified by memcached protocol.
Thus, no need to store it as a 64-bit value. When the value is needed,
convert it to the target type. Change intended to save space from
item structure.
In addition, there is no need to insert an entry into _alive when
expiration time is zero, meaning item will never expire.
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
Flashcached integration was done relying on certain similarities between
flashcached and memcached. Old assumptions no longer hold.
As a result, the current code is terrible to integrate the slab allocator
into it, while keeping flashcached alive.
This patch reverts flashcached from memcached. It should be re-integrated
in the future, but definitely in a better way.
httpd uses recursion for its read loop:
future<> read() {
_read_buf.consume().then([] {
...
if more work:
return read();
});
}
However, after error handling was added, it looks like this:
future<> read() {
_read_buf.consume().then([] {
...
if more work:
return read();
}).rescue(...);
}
The problem is that rescue() is called for every iteration of the loop,
instead of for the loop in its entirety. This means that a rescue
continuation is allocated for every processed request, but they will only
be called after the entire loop terminates. This results in tons of
allocated memory.
Fix by moving error handling to the end of the loop (and incidentally using
do_until() instead of recursion).
I found wrk sometimes sends RST instead a FIN to close a connection. In
this case, we will reset the connection and go to CLOSED state. However
httpd will not delete this, so we will have leaked connections in CLOSED
state.
Fix by handling the exception and sending an empty response as we do in
EOF case. Here we do not pass the exception to upper layer again,
otherwise httpd will be very noise.
The current shared_ptr implementation is efficient, but does not support
polymorphic types.
Rename it in order to make room for a polymorphic shared_ptr.
size of the sstring _ascii_prefix should also be added when computing
item footprint. Without this change, reclaimer would end up evicting
more than needed.
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
As thrift does not support pipelining, the server is very simple. It
implements the thrift framed transport, where each message is preceded
by a four-byte message size header.
Where possible, throw an exception instead of returning an uninitialized
value.
Where not possible (if the method does not throw), return a "dummy" string.
