Replication reconfiguration used to work as follows: upon receiving a
new config disconnect from all the existing masters and try to connect
to all the masters from the new config.

This lead to instances doing extra work when old config and new config
had the same nodes in them: instead of doing nothing, tarantool
reinitialized the connection.

There was another problem: when an existing connection is broken, master
takes some time to notice that. So, when replica resets the connection,
it may try to reconnect faster than the master is able to notice its
absence. In this case replica wouldn't be able to reconnect due to
`duplicate connection with the same replica UUID`. So replication would
stop for a replication_timeout, which may be quite large (seconds or
tens of seconds).

Let's prevent tarantool from reconnecting to the same instance, if there
already is a working connection.

Closes #4669

Once an anonymous replica tries to register, it reconnects to every
other instance in its replication list in order to receive updated
ballots and choose someone to register on.

Make the instance wait until it connects to quorum before letting it
choose the node to register on.

Since the function arguments are always sequential in the array of all
VDBE MEMs, we don't need to store the position of each argument. The
position of the first MEM and the number of arguments are sufficient to
describe all the arguments.

Part of #4145

This patch removed MEM_TYPE_AGG, which is no longer used due to recent
changes.

Part of #4145

This patch removes copying of the result in the finalizers of the SQL
built-in aggregate functions.

Part of #4145

Part of #4145

Part of #4145

Part of #4145

Part of #4145

Part of #4145

Part of #4145

We don't need this function, since it is easier to call finalizers
directly. This patch also allows us to make further simplifications.

Needed for #4145

This patch introduces the mem_append() function. This function appends
the specified string to the end of the STRING or VARBINARY contained in
MEM. In case MEM needs to increase the size of allocated memory,
extra memory is allocated in an attempt to reduce the total number of
allocations.

Needed for #4145

This patch makes it easier to get a collation by a function.

Needed for #4145

This patch moves the initialization of sql_context out of the VDBE. This
allows us to remove the opcodes OP_BuiltinFunction0 and OP_AggStep0,
which work in a rather strange way. Moreover, due to the changes these
opcodes make to the VDBEs, it is possible that the estimated size of the
VDBE may change during execution of VDBE, which could lead to various
problems.

Needed for #4145

This patch makes OP_FunctionByName, OP_AggStep and OP_BuiltinFunction to
use register P1 for the number of arguments instead of register P5. This
makes it easier to use these opcodes.

Needed for #4145

This patch fixes possible undefined behavior during the implicit cast of
INTEGER to DOUBLE. The problem is, if the INTEGER is close enough to
2^64, it will be cast to 2^64 when it is cast to DOUBLE. Since we have a
check for loss of precision, this will cause this DOUBLE to be cast to
an INTEGER, which will result in undefined behavior since this DOUBLE is
outside the range of INTEGER.

This patch removes zeroblob optimization from SQL code. This
optimization complicates the code, and there is almost no profit from
it.

Closes #6113
Needed for #4145

This patch extends the 'integration.yml' workflow and adds a new
workflow call for running tests to verify integration between tarantool
and the avro-schema module.

Part of #5265
Part of #6056
Closes #6558

This patch extends the 'integration.yml' workflow and adds a new
workflow call for running tests to verify integration between tarantool
and the metrics module.

Part of tarantool/tarantool#5265
Part of tarantool/tarantool#6056
Closes tarantool/tarantool#6526

*.inprogress files shouldn't be deleted during normal GC, because they
may be in use. E.g. GC may happen to run while WAL is rotating xlog;
if GC removes the transient xlog.inprogress file created by WAL (see
xdir_create_xlog), WAL will fail to rename it and abort the current
transaction.

Initially, inprogress files were removed only after recovery. For this
reason, xdir_collect_inprogress, which is used for deleting inprogress
files, accesses FS directly, without COIO. This was changed by commit
5aa243de ("recovery: build secondary
index in hot standby mode") which moved xdir_collect_inprogress from
memtx_engine_end_recovery to memtx_engine_collect_garbage so that a hot
standby instance doesn't delete inprogress files of the master instance
by mistake.

To fix this issue, let's move xdir_collect_inprogress back where it
belongs, to engine_end_recovery, and introduce a new callback for memtx
to build its secondary keys before entering the hot standby mode -
engine_begin_hot_standby.

Let's also remove engine_collect_garbage from gc_init, which was added
there by the aforementioned commit, probably to make tests pass.

The bug was reported by the vinyl/deferred_delete test (#5089).

Closes #6554

Quorum.test.lua was migrated to luatest.
It was divided into several tests.

Delete quorum.test.lua, fix suite.ini in replication tests.

Part of tarantool/test-run#304

Use luatest for checking correctness behavioral for encode/decode
functions

Delete msgpack.test.lua.

Part of tarantool/test-run#304

The commit includes a few helpers files for luatest infrastructure.
'Server' based on luatest Server with additional functionality like
waiting Server for start, create Server's own env including box.cfg
provided by test.

Servers could be built and added in a cluster (cluster.lua file).

Asserts.lua is additional checks, which are useful for many tests.

Helpers are supportive function, could be also used for many tests.

Part of tarantool/test-run#304

Same as for local transactions, timeout for iproto transactions
was implemented. If timeout is not specified in client request
it's sets to box.cfg.txn_timeout, which specified on server side.

Closes #6177

@TarantoolBot document
Title: ability to set timeout for iproto transactions was implemented
A new `IPROTO_TIMEOUT 0x56` key has been added. Currently it is used to
set a timeout for transactions over iproto streams. It is stored in the
body of 'IPROTO_BEGIN' request. If user want's to specify timeout using
netbox (3s for example), he should use 'stream:begin({timeout = 3}).

Client code errors or manual mistakes can create transactions that are
never closed. Such transaction will work as a memory leak. Implement
timeout for transactions after which they are rolled back.

Part of #6177

@TarantoolBot document
Title: ability to set timeout for transactions was implemented
Previously transactions are never closed until commit or rollback.
Timeout for transactions was implemented after which they are rolled
back. For these purpose, in `box.begin` the optional table parameter
was added. For example if user want to start transaction with timeout
3s, he should use `box.begin({timeout = 3})`. Also was implement new
configuration option `box.cfg.txn_timeout` which determines timeout for
transactions, for which the timeout was not explicitly set. By default
this option is set to infinity (TIMEOUT_INFINITY = 365 * 100 * 86400).
Also in C API was added new function to set timeout for transaction -
'box_txn_set_timeout'.

Previously, if a yield occurs for a transaction that does not
support it, we roll back all its statements, but still process
its new statements (they will roll back with each yield). Also,
the transaction will be rolled back when a commit is attempted.
Now we stop processing any new statements right after first yield,
if transaction doesn't support it. This is done so that when we
implement timeout for transactions, the rollback of the transaction
at its expiration and at yield has the same behavior.

Part of #6177

We are going to implement timeout for transaction, after which it
will be rolled back. The timeout starts counting from the moment of
the first yield. Previously `txn_on_yield` trigger installed only
in case when engine does not support yields for transactions. Now it
is installed when transaction is created, but if transaction supports
yields it doesn't do anything. In the following patches, we will use
this trigger to start the transaction timeout countdown.

Part of #6177

There are different warnings after adding checks and luatest submodules.

Follows-up tarantool/test-run#304

This patch extends the 'integration.yml' workflow and adds a new
workflow call for running tests to verify integration between tarantool
and the smtp module.

Part of #5265
Part of #6056
Closes #6523

New function box.txn_id(), which returns the id of the current transaction if
called within a transaction, nil otherwise.

Closes #6396

@TarantoolBot document
Title: new function box.txn_id()
New function in module box:  box.txn_id(), which returns the id of the current
transaction if called within a transaction, nil otherwise.

A simple example is in the test-run source tree
(`test/test-luatest/smoke_check_test.lua`).

https://github.com/tarantool/test-run/issues/304
https://github.com/tarantool/test-run/pull/310

The idea of these changes is to run testing workflows on self-hosted
ubuntu-20.04 machines instead of GitHub ubuntu-20.04 runners. It is
planned to use GitHub ubuntu-20.04 runners only for integration testing
of tarantool with a module/connector where ephemeral environments will
allow us avoiding various cleanup pains on self-hosted runners like

    - if: always()
      run: sudo apt-get -y purge 'tarantool*'

or

    - if: always()
      run: rm -rf .rocks

or

    - if: always()
      run: rm -rf pytest-venv

Also, switch workflows running on GitHub ubuntu-18.04 runners to
self-hosted ubuntu-20.04 machines.

Bump debian/compat to 10 since 9 is deprecated. Bump minimal required
debhelper to 10 (except for Ubuntu Trusty and Xenial) since it is the
recommended practice for compatibility level setup.

Closes #6393

The maximal unix socket file length is 108 symbols on Linux, so
we should decrease file name to fit in this size.

The session can be closed while kharon is travelling between tx and
iproto. If this happens, kharon shouldn't go back to iproto when it
returns to tx, even if there are pending pushes, because the connection
is going to be freed soon.

Thanks to @Gerold103 for the simple fix.

Closes #6520

This patch removes the DECIMAL truncation in LIMIT and OFFSET, because
according to the implicit casting rules, DECIMAL with digits after the
decimal point cannot be implicitly cast to INTEGER.

Closes #6485

This patch fixes an assertion when casting DECIMAL value less than 0 and
greater than -1 to INTEGER.

Part of #6485

In case the DECIMAL value is implicitly cast to INTEGER during a search
using an index, it was possible that DECIMAL would be truncated, which
is not correct according to the implicit cast rules. This patch removes
this truncation.

Part of #6485

In case user enters invalid listen address, tarantool closes previous listen
socket, but bind on invalid address fails also, so tarantool becames blind -
no listening socket at all. This patch fixed this behaviour, now tarantool
still listen old listen address.

Closes #6092