Blackhole is a very simple engine that allows to create spaces that may
written to, but not read from. It only supports INSERT/REPLACE requests.
It doesn't support any indexes hence SELECT is impossible. It does check
space format though and supports on_replace and before_replace triggers.

The whole purpose of this new engine is writing arbitrary rows to WAL
without storing them anywhere. In particular, we need this engine to
write deferred DELETEs generated for vinyl spaces to WAL.

Needed for #2129

Needed for blackhole spaces, which don't support indexes per se, but
still may have a before_replace trigger installed.

Currently, the way txn_stmt::old_tuple and new_tuple are referenced
depends on the engine. For vinyl, the rules are straightforward: if
txn_stmt::{old_tuple,new_tuple} is not NULL, then the reference to the
corresponding tuple is elevated. Hence when a transaction is committed
or rolled back, vinyl calls tuple_unref on both txn_stmt::old_tuple and
new_tuple. For memtx, things are different: the engine doesn't
explicitly increment the reference counter of the tuples - it simply
sets them to the newly inserted tuple and the replaced tuple. On commit,
the reference counter of the old tuple is decreased to delete the
replaced tuple, while on rollback the reference counter of the new tuple
is decreased to delete the new tuple.

Because of this, we can't implement the blackhole engine (aka /dev/null)
without implementing commit and rollback engine methods - even though
such an engine doesn't store anything it still has to set the new_tuple
for on_replace trigger and hence it is responsible for releasing it on
commit or rollback. Since commit/rollback are rather inappropriate for
this kind of engine, let's instead unify txn_stmt reference counting
rules and make txn.c unreference the tuples no matter what engine is.
This doesn't change vinyl, because it already conforms. For memtx, this
means that we need to increase the reference counter when we insert a
new tuple into a space - not a big deal as tuple_ref is almost free.

By now, replace function takes new tuple and old tuple as arguments, instead
of single txn_stmt. It has been done in order to avoid abusing txn_stmt:
the only usage was extracting tuples from it.
As a result, this function can be used by ephemeral tables
without any patching.

(cherry picked from commit 880712c9)

They are fairly small and closely related so let's merge them and call
the result sysview.[hc].

This should reduce maintenance burden and help us introduce a new
engine.

It will be used to check if a replica fell too much behind its peers and
so needs to be rebootstrapped.

Needed for #461

Not needed anymore as we now use the new IPROTO_VOTE command instead of
IPROTO_VOTE_DEPRECATED. Let's remove it altogether and reuse its code
for IPROTO_BALLOT (they are never decoded together so no conflict should
happen). Worst that can happen is we choose a read-only master when
bootstrapping an older version of tarantool.

This patch contains some follow-up fixes for fe8ae607
("Introduce IPROTO_VOTE command"):
 - Rename 'status' to 'ballot' everywhere in the comments.
 - Rename IPROTO_REQUEST_VOTE to IPROTO_VOTE_DEPRECATED and
   iproto_reply_request_vote to iproto_reply_vote_deprecated
   to emphasize the fact that this iproto command has been
   deprecated and IPROTO_VOTE should be used instead.
 - Only send an IPROTO_VOTE request to a master if it is
   running tarantool 1.10.1 or newer.

The new command is supposed to supersede IPROTO_REQUEST_VOTE, which is
difficult to extend, because it uses the global iproto key namespace.
The new command returns a map (IPROTO_BALLOT), to which we can add
various information without polluting the global namespace. Currently,
the map contains IPROTO_BALLOT_IS_RO and IPROTO_BALLOT_VCLOCK keys,
but soon it will be added info needed for replica rebootstrap feature.

Needed for #461

_say function was called with invalid arguments.
Thank @sorc1 for patch.

Closes #3433.

Strdup may silently fail without any message from tarantool.
Patch adds this checks.

Strings containing "true" and "false" were converted
to a boolean type when serializing. Fixed.
Example:
type(yaml.decode(yaml.encode('false'))) == string
type(yaml.decode(yaml.encode('true'))) == string

Closes #3476.

Function tonumber64 has worked incorrectly with values less
than INT64_MAX.
Now it works in the interval [INT64_MAX, UINT64_MAX] returning
nil otherwise.

Closes #3466.

Net.box didn't pass options containing iterator to
server side.
There were also invalid results for two :count tests in
net.box.result file.

Thanks @ademenev for contributing problem and help with
problem locating.

Closes #3262.

Currently, this function takes a single boolean argument, but I'm
planning to add another one. Since two bool arguments look rather
confusing, let's turn this arguments into flags.

Needed for #461

A small cleanup to avoid a potentially inefficient use of
gc_consumer_vclock().

Follow up on a patch for gh-461.

In order to check if a replica needs to be rebootstrapped, we need to
know the vclock of the oldest WAL stored on the master, but the garbage
collector works with signatures and hence can't report the vclock it was
last called for. Actually, all gc users have a vclock and can pass it
instead of signature so it's pretty easy to switch garbage collection
infrastructure to vclock.

Needed for #461

We will need it in other places.

 - Remove extra scan of the WAL directory from local_recovery() - we
   scan the directory in recovery_end_vclock() hence we can skip scan in
   recover_remaining_wals() by passing scan_dir = false.

 - Rename recovery_end_vclock() to recovery_scan() to emphasize the fact
   that this function scans the WAL directory. Write a comment to this
   function.

 - Add comments to wal.c explaining why we scan the WAL directory there.

Follow-up 0695fbbb ("box: retrieve end vclock before starting local
recovery").

To bring crash_expected option of "start server" command.

There were no checks for granting and revoking a non-existent
privilege or a privilege to a non-existent entity.
Added the checks, and a test case.

Closes #3417

Net.box didn't pass options containing iterator to
server side.
There were also invalid results for two :count tests in
net.box.result file.

Thanks @ademenev for contributing problem and help with
problem locating.

Closes #3262.

If is_first_insert flag is set and vy_stmt_type(rv->tuple) equals
IPROTO_DELETE, we free rv->tuple, but then we dereference it via
an on-stack variable to check if we need to turn a REPLACE into an
INSERT or vice versa. Fix this.

This is not necessary, as we can use fiber()->gc, as we usually do.

Move key_def creation to compare_write_iterator_results as it is the
same for all test cases. Performance is not an issue here, obviously, so
we can close our eyes to the fact that now we create a new key def for
each test cases.

The new function inserts a new item into the list at the specified
postion.

If a fiber pool reuses already canceled fiber then the fiber reports an
error for any next request. Now canceled fiber returns and fiber pool
creates a new one.

Fixes #3527

New commit in third_party/libyaml downgrades
required cmake version.

Need to update tests as with fixup in upstrem
commit baf636a74b4b6d055d93e2d01366d6097eb82d90
Author: Tina Müller <cpan2@tinita.de>
Date:   Thu Jun 14 19:27:04 2018 +0200

The closing single quote needs to be indented...
if it's on its own line.

Closes #3275.

Closes #3275.

Found by @ImeevMA

 - Factor out local_recovery() from box_cfg_xc(). Make it setup
   replication and handle local recovery and hot standby cases.
 - Move replication setup in case of initial bootstrap from box_cfg_xc()
   to bootstrap() to make bootstrap() consistent with local_recovery().
 - Move initial snapshot creation from bootstrap() to bootsrap_master()
   and bootstrap_from_master().

Needed for #461

box_sync_replication() can now be called before recovery, right after
box_listen(). This is a step toward detecting if the instance fell too
much behind its peers in the cluster and so needs to be rebootstrapped.

Needed for #461