Closes #1488

Fixes #2190

Handle event loop for every 0.1M of restored snapshot rows. Issue #2108

vinyl expects that entry->res contains a correct signature of the
transaction. We used to sloppily assign it to some non-zero signature
of the last committed transaction in the batch in case of success.
Vinyl expects an exact value, growing monotonically for each next
transaction.

Optimistically promote writer vclock with replica vclock before
write, in hope that the same row is never applied twice. To be
covered with test and addressed in a separate patch (gh-2283).

Fix error code and error message for big tuples. Fixed #2236

Fixes #2092

Use luaL_checkuint64()/luaL_pushuint64() to work with uint64_t values.

Fixes #2096

The dump of index-wide run can start when compaction of one or more
ranges is in progress (see #2209). If we reset the max_dump_size and
compact_priority in compact_complete, there can be the following case:

   compact_prio = x      compact_prio = y > x   compact_prio = 0
    |                 |                       |    => y has lost.
    +-----------------|-----------------------+
    |                 compact                 |
    +-----------------|-----------------------+
         +------------+
         |    dump    |
         +------------+

Reset the compact_priority and max_dump_size in compact_new() and
restore the saved values on abort.

Needed for #2209

For all pages except the last we use its min_key as the left border
and min_key of the next page as the right border. The last page doesn't
have the right neighbour, so there is no way to determine its bounds.
This patch add a right border for the last page to vy_task.

This feature is needed to split correctly index-wide runs into ranges
during compaction (#2209).

                              Index-wide run
               +-------------------------------------------+
               |  page 1  |  page 2  |  page 3  |  page N  |  <--- max key
               +-------------------------------------------+
+-----------+-------------+---------------------+-------------+---------+
| range 1   |   range 2   |       range 3       |   range 4   | range 5 |
+-----------+-------------+---------------------+-------------+---------+

Page N uses dump_task.max_written_key as its right border.

First, the vy_range_get_dump_iterator(), to merge frozen in-memory
indexes.
Second, the vy_range_get_compact_iterator(), to merge fozen
in-memory indexes and some runs.

Needed for #2209

During transition process to the single mem per index architecture we plan
to use special ranges to handle index-wide runs. Add a flag to vy_log to
distinguish between regular ranges and ranges used for index-wide runs.

Needed for #2209

Follow up d08f494e
See #2225

Export API to create key definitions and tuple formats. Now modules
can create custom key defs and custom tuples formats to use
optimized tuple_compare.cc functions for fast tuple comparsion.

Closes #2225

Follow up the previous commit.

vy_log_record.index_id is actually LSN from the time of index creation
whereas vy_log_record.iid is original index_id from data dictionary.
Rename misleading index_id to index_lsn to match the actual state.

Instead of providing high-level helpers (vy_collect_garbage(),
vy_log_relay(), vy_log_backup()), expose vy_recovery API.
This eliminates encapsulation issues (like vy_log having to know
how to format run paths).

Both of the methods need it, but instead of receiving it as an argument,
they store it somewhere within the engine. This eases extraction of
vy_recovery from vy_log, done by the next patch.

vy_recovery_new() reads xlog, which blocks the current fiber, so we
call it from a coeio task. Let's make it use coeio internally.

Rename *.xctl to *.vylog

Moving vylog to the core and naming it xctl in order to store metadata
coming from all engines in it turned out to be a premature move, because
we don't exactly know what format to use, neither do we have a proper
infrastructure yet. Move it back for now. We will get back to it once we
figure out how to implement replication groups.

Introduce Engine::collectGarbage() and backup() callbacks for vinyl, and
call xctl_collect_garbage() and xctl_backup() from them. Also, move
xctl_init(), xctl_free(), xctl_{begin,end}_recovery(), xctl_rotate() to
vinyl. Needed to turn xctl into vinyl-private metadata log.

Introduce Engine::backup() callback and implement it for memtx.
Needed to turn xctl into vinyl-private metadata log.

Rewrite the test case in Lua.

Fixes #1667

* Add comments to all functions and enum members.
* Add XXX_name() functions to get enum names by a code and
  refactor Lua xlog reader.
* Use NULL instead of "" for missing values in XXX_type_strs
  to fix Lua xlog reader.
* Add missing strings to iproto_key_name_strs[].
* Rename row_index into page_index.

Remove map-in-a-map-in-a-map layout and use xrow->body instead.

See #2100

Follow up b3b89649

Follow up 987b20b5
Closes #2258

Fixes #2259

Follow up #2256

Rewrite test using TAP to avoid interference of test-run.

Fixes #2198

Fixes #2257

Now struct key_def contains only key definition - field numbers with types
and format-specific comparators. struct index_def contains corresponding key
definition and index parameters (type, name, and e.g.).

Needed for #2225

Remove unused functions key_list_add_key and key_list_del_key.
Prerequisite for #2225

A run can be deleted by a concurrent compaction task while a run
iterator is reading it via coeio. Currently, we detect this by checking
index and range versions after coeio task completes, which results in
vy_run_iterator being dependant on vy_range. Due to this dependency, we
can't add a run w/o a range to an iterator, which is required to make
in-memory levels per index rather than per range. Let's remove this
dependency by making vy_run_unref() return a boolean flag set if the
run was deleted, and using this to abort run iterator.

Fixes #2063

* remove dead code
* reduce scope of struct recovery *recovery

Fixes #2198