vy_run_iterator_load_page() keeps two most recently read pages. This
makes sense, because we often probe a page for a better match. Keeping
two pages rather than just one makes sure we won't throw out the current
page if probing fails to find a better match. What doesn't make sense
though is cache promotion logic: we keep promoting the page containing
the current key. The comment says:

        /*
         * The cache is at least two pages. Ensure that
         * subsequent read keeps the cur_key in the cache
         * by moving its page to the start of LRU list.
         */
        vy_run_iterator_cache_touch(itr, cur_key_page_no);

The comment is quite misleading. The "cache" contains at most two pages.
Proudly calling this travesty of a cache LRU is downright ridiculous.

Anyway, touching the current page will simply swap the two cached pages
if a key history spans less than two pages, resulting in no performance
gain or loss whatsoever. However, if a key history spans more than two
pages, it will evict a page that is about to be read.

That said, let's get rid of this piece of crap.

vy_run_iterator_next_key() has to special-case LE/LT for the first
and the last page. This is needed, because this function is used by
vy_read_iterator_seek() for starting iteration. Actually, there's no
point for vy_read_iterator_seek() to use vy_read_iterator_next_key() -
vy_read_iterator_next_pos() + vy_read_iterator_find_lsn() would be
enough. Bearing this in mind, simplify vy_run_iterator_next_key().

Inside a docker 'Connection refused' error turns into
'Cannot assign requested address' - because of it netbox test
fails, which searches for 'Connection refused' in logs.

Let search for both.

Follow up #3164

When reconnect fails, it prints error to log. But reconnect can
fail again and again very many times until the connection is
closed.

Lets print the first error message under warn log level, and the
following ones under verbose log level until error will not be
changed.

Closes #3175

If a connection has reconnect_after > 0, then it is never deleted
until it is explicitly closed or reconnect_after is reset. It is
because worker fiber of such connection holds all references
during yield.

Fix it by do not waiting for a next reconnection inside a state
machine - protocol_sm() function must not be infinite in a case
of error.

Closes #3164

When fio.read  from multiple fibers is performed, as fio.read yields before
performing actual read operation and ibuf shared among several fibers
may be corrupted and read data is mixed.

The fix is to create new ibuf for each fio.read call in case
buffer is not specified.

Closes #3187

* Add test on usage run_triggers inside before_replace.
Test verifies that other before_replace triggers within the
same space will be executed but other triggers won't.
* Add test on return old in before_replace.
Test verifies that other before_replace triggers will be executed,
but insertion won't take place and other triggers will be ignored.

Closes #3128

Fix problem: cannot connect to unix binary socket using authentication.
To solve this issue update our uri parser to support following schema:
 login:password@unix/:/path1/path2/path3
Add tests

Closes: #2933

If curl does not have SSL support, don't panic, honor CURL_FIND_REQUIRED
variable, and panic only if it's set.

Correct the grammar in the error message.

On MAC several old curl versions don't support SSL by default.
Try to check it and print error message if so.

Close #3065

Closes #2666

When a field type is specified as numbered key, and a name is
named key, then the type is ignored. For example:
{name = '<name>', '<type>'} - here the '<type>' is ignored and
result space format contains 'any' regardless of <type>.

Fix tuple format field parsing to take this case into account.

Closes #2895

ERRINJ_VY_READ_PAGE and ERRINJ_VY_READ_PAGE_TIMEOUT injections are
used by vinyl/errinj test to check that a page read error is handled
properly. The cache checks if these injections are enabled and bails
out if so. Since commit a31c2c10 ("vinyl: force read view in
iterator in autocommit mode"), this is not necessary, because cache
is not used unless SELECT is called from a transaction, and the above
mentioned test doesn't use transactions. So let's remove the checks.
If we ever enable cache for all SELECTs, we can disable cache in the
test with box.cfg.vinyl_cache instead of using error injections.

Currently, new entries are added to the cache even if the limit is set
to 0, which is obviously incorrect. Fix it. This might be useful for
debugging and/or performance evaluation.

Closes #3172

Make box.cfg.vinyl_cache option dynamically configured. If the new
value is less than the current cache usage, it will block until it
reclaims enough cache entries to fit in the new limit.

If the user terminates tarantool while compaction is in progress,
tarantool won't exit immediately - it will hang until all dump and
compaction tasks that are currently in progress are complete, which
may take quite a while on large data sets. What is especially funny,
once a task has been finished, vinyl will not commit the produced run
file in the vylog, because the event loop has already been stopped,
and so will delete it after restart and schedule the task anew.

This patch makes the scheduler forcefully abort all running tasks
as soon as possible.

Closes #3166

This is pointless as worker threads don't use coio.

vy_run_writer incapsulates logic of writing statements to a run.
It provides API to write statements one by one. It is needed so
that we can abort a run writing task before waiting for it to
finish writing the file.

Edited by @locker:
 - add region_truncate() wherever necessary
 - do not reallocate row index ibuf for each page
 - remove vy_run_write(), use vy_run_writer directly instead

Needed for #3166

If a replica receives some changes then corresponding wal events are
generated and relay fiber is waken up before heartbeat timeout.
But there may be nothing to send if all changes are from the current
relay peer. In this case an applier doesn't receive anything and break a
connection.

Fixes #3160

When iterating over a vinyl index, we move to the next range if the
minimal (in terms of the search criteria) statement among all sources
is outside the current range - see vy_read_iterator_next_key() and
vy_read_iterator_range_is_done(). This is OK for GE/GT/LE/LT, but for
EQ/REQ we should also make sure that the next range actually intersects
with the search key - if it doesn't, there's no point in iterating to
it. We used to have that check, but commit 5e414a73 ("vinyl: read
iterator: do not reopen all sources when range is changed") accidentally
removed it. As a result, unlimited EQ/REQ requests for partial keys read
runs of all ranges and therefore take much longer. This patch brings
this check back.

Add memory occupied by cached slabs to the size reported by
arena_size and arena_used_ratio respectively.

This should make memory monitoring easier:

if items_used_ratio > 0.9 and arena_used_ratio > 0.9 and quota_used_ratio > 0.9 then
    we run out of memory
end

On FreeBSD we have either system iconv (part of libc) or the one
in /usr/local. The first one is not fully compatible with Linux/
OSX iconv and both adds specific prefixes to function names.
So to use them via Lua FFI mechanism, specific names are required.
Proposal fix:
Under FreeBSD link with /usr/local/lib/libiconv.so and add prefix.

Closes gh-3073.

* Add parser of cookies from 'Set-Cookie' header.
* All cookies are stored in response object in cookie table.
* The format of each table element is following:
resp[key] = {value, {option, ...}},
where key, value is cookie key, value
options are array of strings, set-cookie header options,
e.g. HttpOnly, Expires=<date>.

Closes #2801

* delete old small parser with nginx tested one
* functionality is not changed

If a key is updated after a secondary index scan, but before a
primary index lookup, then ignore this update.

Closes #2442

If a column is nullable and is the last defined one (via index parts
or space format), it can be omited on insertion. Such absent fields
are treated as NULLs in comparators and are not stored.

Closes #2988