The SQL_FUNC_SLOCHNG flag was useful for datetime function
that are currently not supported. So it could be removed.

Needed for #2200, #4113, #2233

Renamed OP_Function opcode to OP_BuiltinFunction to introduce a
new OP_Function operation in a new meaning: a new OP_Function
would call Tarantool's function with new port-based API while
legacy OP_BuiltinFunction is an efficient implementation of
SQL Builtins functions.

Needed for #2200, #4113, #2233

Tarantool's SQL engine generates a different VDBE bytecode
for ..COUNT(*).. and ..COUNT(fieldname).. operations:
the first one produces a lightweight OP_Count operation that uses
native mechanism to report the count of record in index while
the second one pessimistically opens a space read iterator and
uses Count aggregate function.

A helper routine is_simple_count decides whether such
optimisation is correct. It used to use SQL_FUNC_COUNT flag to
mark a dummy (non-functional) function entry with 0 arguments.
This patch changes SQL_FUNC_COUNT semantics: now it is a marker
of any COUNT function, while is_simple_count relies on count
of arguments to distinguish aggregate and non-aggregate
functions.

Needed for #2200, #4113, #2233

A new dispatcher function trim_func calls corresponding trim_
function implementation in relation with number of argc - a count
of arguments.

This is an important step to get rid of function's name
overloading required for replace FuncDef cache with Tarantool's
function cache.

Needed for #2200, #4113, #2233

This patch does two things: renames existing scalar min/max
functions and reserves names for them in NoSQL cache.

Moreover it is an important step to get rid of function's name
overloading required for replace FuncDef cache with Tarantool's
function cache.

Closes #4405
Needed for #2200, #4113, #2233

@TarantoolBot document
Title: Scalar functions MIN/MAX are renamed to LEAST/GREATEST

The MIN/MAX functions are typically used only as aggregate
functions in other RDBMS(MSSQL, Postgress, MySQL, Oracle) while
Tarantool's SQLite legacy code use them also in meaning
GREATEST/LEAST scalar function. Now it fixed.

The SQL_PreferBuiltin flag is redundant (because builtin names
are forbidden for UDFs) so we may to remove it.

Needed for #4113, #2200, #2233

Vdbe field ref is a dynamic index over tuple fields storing
offsets to each field and filling the offset array on demand.
It is highly used in SQL, because it strongly relies on fast and
repetitive access to any field, not only indexed.

There is an optimisation for the case when a requested field
fieldno is indexed, and the tuple itself stores offset to the
field in its own small field map, used by indexes. vdbe_field_ref
then uses that map to retrieve offset value without decoding
anything. But when SQL requests any field > fieldno, then
vdbe_field_ref decodes the tuple from the beginning in the worst
case. Even having previously accessed fieldno. But it could
start decoding from the latter.

An updated vdbe_field_ref fetcher class uses a bitmask of
initialized slots to use pre-calculated offsets when possible.
This speed-ups SQL in some corner case and doesn't damage
performance in general scenarios.

Closes #4267

(cherry picked from commit 507f3721)

Before this patch, snapshot interval was set randomly within
checkpoint_interval period. However, after box.snapshot(), the next
snapshot was scheduled exactly checkpoint_interval from the current time.
Many orchestration scripts snapshot entire cluster right after deployment,
to take a backup. This kills randomness, since all instances begin to
count the next checkpoint time from the current time.

Randomize the next checkpoint time after a manual snapshot as well.

Fixes gh-4432

pretest_clean: preserve GREATEST and LEAST built-in functions.

Needed for #4405.

Originally, mask in struct Keyword served to reduce set of reserved
keywords for build-dependent features. For instance, it was allowed to
disable triggers as a compilation option, and in this case TRIGGER
wouldn't be reserved word. Nowadays, our build always comprises all
features, so there's no need in this option anymore. Hence, we can
remove mask alongside with related to it macros.

Closes #4155

It was forgotten to update result file of sql/bind.test.lua
in previous patch. Let's fix that and refresh sql/bind.result with
up-to-date results.

It was decided that for all integer literals we would return "INTEGER"
type, not "UNSIGNED". Accidentally, after substitution of unsigned
binding value type was set to "UNSIGNED". Let's fix that and set
"INTEGER" type.

https://github.com/LuaJIT/LuaJIT/issues/505

wal_sync() simply flushes the tx<->wal request queue, it doesn't
guarantee that all pending writes are successfully committed to disk.
This works for now, but in order to implement replica join off the
current read view, we need to make sure that all pending writes have
been persisted and won't be rolled back before we can use memtx
snapshot iterators. So this patch adds a return code to wal_sync():
since now on it returns -1 if rollback is in progress and hence
some in-memory changes are going to be rolled back. We will use
this method after opening memtx snapshot iterators used for feeding
a consistent read view a newly joined replica so as to ensure that
changes frozen by the iterators have made it to the disk.

Found that on high loaded hosts the test flaky fails at:

[004] --- app/socket.result	Mon Jul 15 07:18:57 2019
[004] +++ app/socket.reject	Tue Jul 16 16:37:35 2019
[004] @@ -1118,7 +1118,7 @@
[004]  ...
[004]  ch:get(1)
[004]  ---
[004] -- true
[004] +- null
[004]  ...
[004]  s:error()
[004]  ---

Found that the test in previous was used for testing the
the channel get() function timeout and the error occurred
on it, but later the checking error changed to:
"builtin/socket.lua: attempt to use closed socket" and the
test became not correct. Because for now it passes when the
socket read function runs before the socket closing, but in
this way read call doesn't wait. In the other way on high
loaded hosts the close call may occure before read call and
in this way read call halts and socket get call returns
'null'. As seen both ways are not correct to check the error.
Decided to remove this subtest.

Check commit ba7a4fee ("Add tests for socket:close closes #360")

Fixes #4354

We will reuse it to relay a snapshot to a newly joined replica.

Memtx iterators never fail, that's why the snapshot iterator interface
doesn't support failures. However, once we introduce snapshot iterator
support for vinyl, we will need a way to handle errors in the API.

It's pointless as we can always access the index via iterator->index.

Now, as vy_lsm and index are basically the same object, we can implement
reference counting right in struct index. This will allow us to prevent
an index from destruction when a space object it belongs to is freed
anywhere in the code, not just in vinyl.

There's no point in having vinyl_engine and vinyl_index wrapper structs
to bind vy_env and vy_lsm to struct engine and index. Instead we can
simply embed engine and index in vy_env and vy_lsm. This will simplify
further development, e.g. this will allow us to move reference counting
from vy_lsm up to struct index so that it can be used in the generic
code.

There's no point in having vinyl_engine and vinyl_index wrapper structs
to bind vy_env and vy_lsm to struct engine and index. Instead we can
simply embed engine and index in vy_env and vy_lsm. This will simplify
further development, e.g. this will allow us to move reference counting
from vy_lsm up to struct index so that it can be used in the generic
code.

Part of #4403

@TarantoolBol document
Title: Document decimal modulo operator

There is now a modulo operator for decimal numbers:
```
a = decimal.new(172.51)
a % 1
---
- '0.51'
...
a % 0.3
---
- '0.01'
...
a % 13.27
---
- '0.00'
...
a % 173
---
- '172.51'
...
a % 72
---
- '28.51'
...
720 % a
---
- '29.96'
...
```

JSON paths has no a strict standard, but definitely there is no
an implementation, allowing to omit '.' after [], if a next token
is a key. For example:

    [1]key

is invalid. It should be written like that:

    [1].key

Strangely, but we even had tests on the invalid case.

Closes #4419

Disable a check whether yaml responses are well-formed for 'core =
tarantool' tests in test-run. The check was unable to handle complex
(dictionary / list) keys in a dictionary, because pyyaml does not
support them.

See also https://github.com/yaml/pyyaml/issues/88

Fixes #4421.

In one place that test sends a packet and expects that it has
arrived two lines below. Under high load it may take more time.
The patch makes the test explicitly wait for the packet arrival.

Closes #4392

There is compile time option PACKAGE in cmake to define
current build distribution info. By default it's
"Tarantool" for the community version and "Tarantool Enterprise"
for the enterprise version.

It's displayed in console greeting and in `box.info().package`,
but, unfortunately, it can't be accessed from Lua before `box.cfg`.

This patch exposes `require('tarantool').package`.

Close #4408

@TarantoolBot document
Title: Extend module "tarantool" with the field "package"

Beside from build info and version, module "tarantool" now provides
"package" field. By default it equals string "Tarantool", but
can differ for other distributions like "Tarantool Enterprise".

Example:

```console
tarantool> require('tarantool')
---
- version: 2.3.0-3-g302bb3241
  build:
    target: Linux-x86_64-RelWithDebInfo
    options: cmake . -DCMAKE_INSTALL_PREFIX=/opt/tarantool-install
-DENABLE_BACKTRACE=ON
    mod_format: so
    flags: ' -fexceptions -funwind-tables -fno-omit-frame-pointer
-fno-stack-protector
      -fno-common -fopenmp -msse2 -std=c11 -Wall -Wextra
-Wno-strict-aliasing -Wno-char-subscripts
      -Wno-format-truncation -fno-gnu89-inline -Wno-cast-function-type'
    compiler: /usr/bin/cc /usr/bin/c++
  pid: 'function: 0x40016cd0'
  package: Tarantool
  uptime: 'function: 0x40016cb0'
...

```

The _func_index space trigger used to reject an insertion of a
tuple that defines an invalid functional index.
As insertion in _index space had been completed before, a garbage
is kept in _index space in such case.

We need to do something with the yelding _func_index trigger(that
rebuilds an index) to wrap all index creation operation in DDL
transaction in further patches (because only the first DDL
operation may yeld now).

This problem could be trivially solved with preparatory
initialization of index_def function ponter: the memtx_tree
index construction would perform all required job in such case.
Therefore the following index rebuild in _func_index trigger
becomes redundant and should be omitted.

In other words, a trivial prefetch operation makes possible
a transactional index creation (with space:create_index operation).

As for index construction during recovery (a lack of function
cache during recovery was the main motivation to introduce
_func_index space), it's workflow is kept unchanged.

Follow up #1250
Needed for #4348
Closes #4401

As per request by Kostja, commit an RFC document with a brief history of
the vinyl metadata log infrastructure, issues it was intended to solve,
problems we are facing now, and possible ways to solve them.

In case an error occurs between relay_start() and cord_costart() in
relay_subscribe(), the relay status won't be reset to STOPPED. As a
result, any further attempt to re-subscribe will fail with ER_CFG:
duplicate connection with the same replica UUID. This may happen, for
example, if the WAL directory happens to be temporarily inaccessible on
the master.

Closes #4399

The function

 | require('console').get_default_output()

requires no arguments. Make it explcicit and print
an error otherwise.

Part-of #3834

Instead of allocating a variable for optional args
testing we should use dot notation instead. Otherwise
it won't work for trivial test case as

```
require('console').set_default_output('lua,block')
require('decimal').new('1234.5678')
```

 | builtin/box/console.lua:47: expected decimal, number or string as 2 argument

and program exits.

Part-of #3834

In output_verify_opts and output_parse we return status variable
to point if function processed without error. This is redundant
we can simply return either error or nil, which is enough.

Part-of #3834

It was decided that null value in SQL by default should be of type
boolean. Justification of such change is that according to ANSI boolean
type in fact has three different values: true, false and unknown. The
latter is basically an alias to null value.

If during creation of constraint its name is not specified, then it is
generated automatically. Occasionally, default names for each type of
constraint turn out to be different. This patch makes them follow the
same pattern: "shortcut"_unnamed_"table_name"_"ordinal_numb". For
instance: fk_unnamed_T1_1 or ck_unnamed_T1_3 etc

If UNIQUE constraint is specified in CREATE TABLE statement and it has
given name, one is mangled with pattern "unique_%s_%d", where %s is
original name of constraint and %d - current iid. For instance:

CREATE TABLE t (id INT PRIMARY KEY, a INT CONSTRAINT i1 UNIQUE);

This statement results in secondary index creation with name
"unique_I1_1". Justification for mangling is that constraint namespace
should be independent from index namespace. However, ALTER TABLE ADD
CONSTRAINT UNIQUE which is alias to CREATE INDEX doesn't mangle name.
What is more, users may wonder why name of index is different from
name of created constraint. Hence, it has been decided to remove this
mangling and create index exactly with specified constraint's name.