2.7.3 is the second [stable][release_policy] version of the 2.7 release
series. It introduces six improvements and resolves 49 bugs since
2.7.2.

The "stable" label means that we have all planned features implemented, and we
see no high-impact issues. However, if you encounter an issue, feel free to
[report it][issues] on GitHub.

[release_policy]: https://www.tarantool.io/en/doc/latest/release/legacy-policy/
[issues]: https://github.com/tarantool/tarantool/issues

Tarantool 2.x is backward compatible with Tarantool 1.10.x in the binary data
layout, client-server protocol, and replication protocol.

[Upgrade][upgrade] using the `box.schema.upgrade()` procedure to unlock
all the new features of the 2.x series.

[upgrade]: https://www.tarantool.io/en/doc/latest/book/admin/upgrades/

* Provide information about state of synchronous replication via
  `box.info.synchro` interface (gh-5191).

* Introduced support for `LJ_DUALNUM` mode in `luajit-gdb.py` (gh-6224).

* The new method `table.equals` compares two tables by value with respect to the
  `__eq` metamethod.

* Descriptions of type mismatch error and inconsistent type error have become more
  informative (gh-6176).

* Removed explicit cast from `BOOLEAN` to numeric types and vice versa (gh-4770).

* Removed explicit cast from `VARBINARY` to numeric types and vice versa (gh-4772,
  gh-5852).

* Fixed a bug due to which a string that is not `NULL` terminated could not be
  cast to `BOOLEAN`, even if the conversion should be successful according to the
  rules.

* Fedora 34 builds are now supported. (gh-6074)

* Fedora 28 and 29 builds are no longer supported.

* **\[Breaking change\]** `fiber.wakeup()` in Lua and `fiber_wakeup()` in C became
  NOP on the currently running fiber. Previously they allowed to "ignore" the
  next yield or sleep, which resulted in unexpected spurious wake-ups.
  Calling these functions right before `fiber.create()` in Lua or `fiber_start()` in C
  could lead to a crash (in debug build) or undefined behaviour (in release build). (gh-6043)

  There was a single use case for the previous behaviour: rescheduling in the same event loop
  iteration, which is not the same as `fiber.sleep(0)` in Lua and
  `fiber_sleep(0)` in C. This could be done in the following way:

  in C:
  ```C
  fiber_wakeup(fiber_self());
  fiber_yield();
  ```
  and in Lua:
  ```Lua
  fiber.self():wakeup()
  fiber.yield()
  ```

  To get the same effect in C, one can now use `fiber_reschedule()`.
  In Lua it is now impossible to directly reschedule the current fiber in the same event loop
  iteration.
  There is a way to reschedule self through a second fiber, but we strongly discourage doing so:

  ```Lua
  -- don't use this code
  local self = fiber.self()
  fiber.new(function() self:wakeup() end)
  fiber.sleep(0)
  ```

* Fixed memory leak on each `box.on_commit()` and `box.on_rollback()` (gh-6025).

* `fiber_join()` now checks if the argument is a joinable fiber.
  Abscence of this check could lead to unpredictable results.
  Note that the issue affects C level only;
  in Lua interface `fiber:join()` the protection is
  turned on already.

* Now Tarantool yields when scanning `.xlog` files for the latest applied vclock
  and when finding the right place in `.xlog`s to start recovering. This means
  that the instance becomes responsive right after `box.cfg` call even when an empty
  `.xlog` was not created on the previous exit.

  This also prevents relay from timing out when a freshly subscribed replica
  needs rows from the end of a relatively long (hundreds of MBs) `.xlog`
  (gh-5979).

* The counter in `x.yM rows processed` log messages will no longer reset on each newly
  recovered `xlog`.

* Fixed invalid results produced by `json` module's `encode` function when it
  was used from the Lua garbage collector.
  For instance, this could happen in functions used as `ffi.gc()`. (gh-6050)

* Fixed a bug when memtx mvcc crashed during reading uncommitted DDL. (gh-5515)

* Fixed a bug when memtx mvcc crashed if an index was created in transaction (gh-6137)

* Fixed a crash in MVCC during simultaneous update of a key in different transactions (gh-6131)

* Fixed segmentation fault with mvcc when entire space was updated concurrently (gh-5892)

* Fixed crash in case of reloading a compiled module when the
  new module lacks some of functions which were present in the
  former code. In turn this event triggers a fallback procedure
  where we restore old functions but instead of restoring each
  function we process a sole entry only leading to the crash
  later when these restored functions are called (gh-5968).

* Fixed a bug with failed assertion after stress update of the same key. (gh-6193)

* Fixed a crash if you call box.snapshot during an incomplete transaction (gh-6229)

* Fixed console client connection breakage if request times out (gh-6249).

* Added missing broadcast to net.box.future:discard() so that now fibers
  waiting for a request result are woken up when the request is discarded
  (gh-6250).

* `box.info.uuid`, `box.info.cluster.uuid`, and `tostring(decimal)` with any
   decimal number in Lua sometimes could return garbage if `__gc` handlers are
  used in user's code (gh-6259).

* Fixed an error message that happened in very specific case
  during mvcc operation (gh-6247)

* Fixed a repeatable read violation after delete (gh-6206)

* Fixed a bug when hash select{} was not tracked by mvcc engine (gh-6040)

* Fixed a crash in mvcc after drop of a space with several indexes (gh-6274)

* Fixed a bug when GC at some state could leave tuples in secondary indexes  (gh-6234)

* Disallowed yields after DDL operations in MVCC mode. It fixes crash which takes
  place in case several transactions refer to system spaces (gh-5998).

* Fixed bug in MVCC connected which happens on rollback after
  DDL operation (gh-5998).

* Fixed a bug when rollback resulted in unserializable behaviour (gh-6325)

* Fixed possible keys divergence during secondary index build which might
  lead to missing tuples in it (gh-6045).

* Fixed a race between Vinyl garbage collection and compaction resulting in
  broken vylog and recovery (gh-5436).

* Fixed use after free in relay thread when using elections (gh-6031).

* Fixed a possible crash when a synchronous transaction was followed by an
  asynchronous transaction right when its confirmation was being written
  (gh-6057).

* Fixed an error when a replica, at attempt to subscribe to a foreign cluster
  (with different replicaset UUID), didn't notice it is not possible, and
  instead was stuck in an infinite retry loop printing an error about "too
  early subscribe" (gh-6094).

* Fixed an error when a replica, at attempt to join a cluster with exclusively
  read-only replicas available, instead of failing or retrying just decided to
  boot its own replicaset. Now it fails with an error about the other nodes
  being read-only so they can't register it (gh-5613).

* When an error happened during appliance of a transaction received from a
  remote instance via replication, it was always reported as "Failed to write
  to disk" regardless of what really happened. Now the correct error is shown.
  For example, "Out of memory", or "Transaction has been aborted by conflict",
  and so on (gh-6027).

* Fixed replication stopping occasionally with `ER_INVALID_MSGPACK` when replica
  is under high load (gh-4040).

* Fixed a cluster sometimes being unable to bootstrap if it contains nodes with
  `election_mode` `manual` or `voter` (gh-6018).

* Fixed a possible crash when `box.ctl.promote()` was called in a cluster with
  >= 3 instances, happened in debug build. In release build it could lead to
  undefined behaviour. It was likely to happen if a new node was added shortly
  before the promotion (gh-5430).

* Fixed a rare error appearing when MVCC (`box.cfg.memtx_use_mvcc_engine`) was
  enabled and more than one replica was joined to a cluster. The join could fail
  with the error `"ER_TUPLE_FOUND: Duplicate key exists in unique index
  'primary' in space '_cluster'"`. The same could happen at bootstrap of a
  cluster having >= 3 nodes (gh-5601).

* Fixed a rare crash with the leader election enabled (any mode except `off`),
  which could happen if a leader resigned from its role at the same time as some
  other node was writing something related to the elections to WAL. The crash
  was in debug build and in the release build it would lead to undefined
  behaviour (gh-6129).

* Fixed an error when a new replica in a Raft cluster could try to join from a
  follower instead of a leader and failed with an error `ER_READONLY` (gh-6127).

* Fixed optimization for single-char strings in `IR_BUFPUT` assembly routine.

* Fixed slots alignment in `lj-stack` command output when `LJ_GC64` is enabled
  (gh-5876).

* Fixed dummy frame unwinding in `lj-stack` command.

* Fixed detection of inconsistent renames even in the presence of sunk values
  (gh-4252, gh-5049, gh-5118).

* Fixed the order VM registers are allocated by LuaJIT frontend in case of
  `BC_ISGE` and `BC_ISGT` (gh-6227).

* When error is raised during encoding call results, auxiliary lightuserdata
  value is not removed from the main Lua coroutine stack. Prior to the fix it
  leads to undefined behaviour during the next usage of this Lua coroutine
  (gh-4617).

* Fixed Lua C API misuse, when the error is raised during call results encoding
  on unprotected coroutine and expected to be catched on the different one, that
  is protected (gh-6248).

* Fixed possibility crash in case when trigger removes itself.
  Fixed possibility crash in case when someone destroy trigger,
  when it's yield (gh-6266).

* User-defined functions can now return VARBINARY to SQL as result (gh-6024).

* Fixed assert on cast of DOUBLE value that greater than -1.0 and less than 0.0
  to INTEGER and UNSIGNED (gh-6255).

* Removed spontaneous conversion from INTEGER to DOUBLE in a field of type
  NUMBER (gh-5335).

* All arithmetic operations can now only accept numeric values (gh-5756).

* Fix MVCC interaction with ephemeral spaces: TX manager now ignores such
  spaces (gh-6095).

* Fixed a loss of tuple after a conflict exception (gh-6132)

* Fixed a segfault in update/delete of the same tuple (gh-6021)