If a vylog record doesn't get flushed to disk due to an error, objects
it refers to (index->key_def, range->begin and range->end) may get
destroyed, resulting in a crash. To avoid that, we must copy those
objects to vylog buffer.

Closes #2532

 - Remove tx and cursor latencies as they are useless - they actually
   account how long a tx/cursor was open, not latencies.
 - Remove vy_stat->get_latency as it doesn't account latency of select,
   besides we now have per index read latency.
 - Remove vy_stat->dumped_statements and dump_total as these statistics
   are reported per index as well.
 - VY_STAT_TX_OPS is currently unused (always 0). Let's use it for
   accounting the total number of statements committed in tx instead of
   vy_stat->write_count.

index.info() is supposed to show index stats, not options.
box.space.<space_name>.index.<index_name>.options looks like
a better place for reporting index options.

Needed for #1662

This patch adds 'latency' field to index.info. It shows the latency of
reads from the index. The latency is computed as 99-percentile of all
delays incurred by vy_read_iterator_next().

Needed for #1662

Replace box.info.vinyl().performance.upsert_{squashed,applied} with per
index index.info().upsert.{squashed,applied}.

Needed for #1662

Add the following counters to index.info:

  lookup                # number of lookups (read iter start)
  get                   # number of statements read (read iter next)
    rows
    bytes
  put                   # number of statements written
    rows
    bytes

Needed for #1662

closes gh-2516

This patch adds the following counters to index.info:

  txw
    count               # number of statements in the TX write set
      rows
      bytes
    iterator
      lookup            # number of lookups in the TX write set
      get               # number of statements returned by the iterator
        rows
        bytes

Needed for #1662

This patch adds the cache section to index.info with the following
counters in it:

  cache
    rows                # number of tuples in the cache
    bytes               # cache memory size
    lookup              # lookups in the cache
    get                 # reads from the cache
      rows
      bytes
    put                 # write to the cache
      rows
      bytes
    invalidate          # overwrites in the cache
      rows
      bytes
    evict               # evictions due to memory quota
      rows
      bytes

Needed for #1662

Using vy_quota, which was implemented to support watermarking,
throttling, timeouts, for accounting cached tuples is an overkill.
Replace it with mem_used and mem_quota counters.

This patch adds the following counters to the disk section index.info:

  dump                  # dump statistics:
    count               #   number of invocations
    in                  #   number of input statements
      rows
      bytes
    out                 #   number of output statements
      rows
      bytes

  compact               # compaction statistics:
    count               #   number of invocations
    in                  #   number of input statements
      rows
      bytes
    out                 #   number of output statements
      rows
      bytes

Needed for #1662

Replace box.info.vinyl().performance.iterator.{run,mem} global counters
with the following per index counters:

  memory
    iterator
      lookup            # number of lookups in the memory tree
      get               # number of statements returned by mem iterator
        rows
        bytes

  disk
    iterator
      lookup            # number of lookups in the page index
      get               # number of statements returned by run iterator
        rows
        bytes

      bloom             # number of times bloom filter
        hit             #   allowed to avoid a disk read
        miss            #   failed to prevent a disk read

      read              # number of statements actually read from disk
        rows
        bytes
        bytes_compressed
        pages

Needed for #1662

It's useless - it only checks that certain counters are present, but
doesn't give a damn about what they show. At the same time, I have to
update its output every time I modify vinyl statistics, which I'm doing
pretty often these days. So let's ditch it - I'll rewrite it from
scratch after I'm done reworking vinyl statistics.

gh-2520: add comments explaining the test case for gh-2520 (upsert
caching).

Use a tuple cache to turn an UPSERT in the PREPARE, if the cache
contains a tuple with the exact same key. The UPSERT can be applied
to the cached tuples, because
1. The cache always contains only REPLACE statements;
2. The cache always contains only newest statements.

Closes #2520

When an UPSERT is prepared, it can use a cached statement to be
turned into REPLACE. But now it doesn't use the cache.

Test for #2520

Minor style fixes to improve code readability. In scope of gh-2529.

Do not unlock endpoint until a flushing async message is sent and do not
destroy endpoint until last pipe release endpoint lock. Fixed #2529

* use name_len and sz consistently across all patches working with names
  and lengths
* do not delete user_def for a system user during init
* use calloc(), since we're using it for index_def as well.

Need for #944

In scope of gh-2547 (lost of space access control lists during truncate).

* use an existing index_def from the new space instead.

IMO makes the code a bit easier to follow.

In scope of work on gh-944 (variable length object names).

* we use name_len for name length in most of the places,
  len is a widespread abbreviation for length

* add comments

Needed for #944

Malformed MessagePack can cause `int k` counter overflow
inside mp_check()/mp_next().

See https://github.com/tarantool/nginx_upstream_module/issues/79
See https://github.com/rtsisyk/msgpuck/issues/16
Closes #2540

In case of default log output
flag o_NONBLOCK is not set to descriptor

Follow up 15a9af26

exp2(64) <= UINT64_MAX is true due to type conversion.
Use exp2(64) instead of UINT64_MAX (optimized out even on -O0).

Fixes buggy box/indices_any_type.test.lua on x86_64

Closes #2472

ffi.new('long', x) and ffi.new('unsigned long', x) uses arbitratry
user-defined ctypeid instead of built-in CTID_INT32 and CTID_UINT32.
Our tonumber64() implementation is not ready for that. Remove these
two test cases and move forward. Nobody cares.

Fixes box/misc.test.lua on i386 and armhf

Follow up #2459