MB-8496: Don't require a value for non-resident meta-data

This change removes the requirement that a non-resident item
needs to have a blob that contains the valur length. This
change introduces a new flag that signals if an item has been
deleted. This change will also reduce meta data by 16 bytes for
each non-resident meta item.

Change-Id: I0d8cbcfba6415c5ff1d61610c783ae517b48848c
Reviewed-on: http://review.couchbase.org/27034
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
MB-8497: Don't track alignment for stored value size function

This code was an attempt at making the sizeof memory accounting
more accurate. We don't use this type of accounting anymore and
this actually makes things much more difficult to keep track of
since we do not adjust for alignment everywhere. On top of this
not all memory allocations are done at 8 byte intervals so this
is technically not even correct code.

Change-Id: I2ddac215bab6803643123630dd146ccd4a49fc1e
Reviewed-on: http://review.couchbase.org/27035
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
MB-8497: Remove unnecessary memory accounting code

This extra code was needed because of the alignment stuff
in the previous commit. The new code actually gets the same
numbers but using less lines of code and less atomic ops.

Change-Id: Icb15a1d07d93058f3c3d0bdc2307ac6eee698342
Reviewed-on: http://review.couchbase.org/27036
Reviewed-by: Jin Lim <jin@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>
MB-8516: Change seqNum to revSeqno in QueuedItem class

We have two different sequence numbers that we will be working with
in ep-engine and it is very confusing to figure out which on we are
talking about when the variable name is specific. The xdcr sequence
number should be revSeqno when it is used in order to distiguish it
from the by sequence number.

Change-Id: I8e2a2764deb9ffc01d0dd43c9ee5d950196a88aa
Assign sequence number in ep-engine

Change-Id: I10e841e2c6f52d4543a1feb8c708a697226fea3f
Add the by sequence number to the tap engine specific section

Change-Id: I501bd9b044e929bda324dd8cb2c2370c9900029f
Backfills are only from disk

This removes the memory backfill that was used when more than 90%
of the items are resident in memory. We cannot use that mechanism
anymore because we need to ensure that items are sent in order of
increasing sequence number.

Change-Id: I6d1e1994ce558d3cba45693d82e7d51c280b0704
Add by sequence number to QueuedItem class

Change-Id: I09a5f6178e04899a413e9382272749ee79cd08f7