Re: [Tarantool-patches] [PATCH 5/9] util: introduce yielding table functions

[Oleg Babin via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Thanks for your patch 1 comment below.

On 10/02/2021 02:46, Vladislav Shpilevoy wrote:
> The patch adds functions table_copy_yield and table_minus_yield.
>
> Yielding copy creates a duplicate of a table but yields every
> specified number of keys copied.
>
> Yielding minus removes matching key-value pairs specified in one
> table from another table. It yields every specified number of keys
> passed.
>
> The functions should help to process huge Lua tables (millions of
> elements and more). These are going to be used on the storage in
> the new GC algorithm.
>
> The algorithm will need to keep a route table on the storage, just
> like on the router, but with expiration time for the routes. Since
> bucket count can be millions, it means GC will potentially operate
> on a huge Lua table and could use some yields so as not to block
> TX thread for long.
>
> Needed for #147
> ---
>   test/unit/util.result   | 113 ++++++++++++++++++++++++++++++++++++++++
>   test/unit/util.test.lua |  49 +++++++++++++++++
>   vshard/util.lua         |  40 ++++++++++++++
>   3 files changed, 202 insertions(+)
>
> diff --git a/test/unit/util.result b/test/unit/util.result
> index 096e36f..c4fd84d 100644
> --- a/test/unit/util.result
> +++ b/test/unit/util.result
> @@ -71,3 +71,116 @@ test_run:grep_log('default', 'reloadable_function has been started', 1000)
>   fib:cancel()
>   ---
>   ...
> +-- Yielding table minus.
> +minus_yield = util.table_minus_yield
> +---
> +...
> +minus_yield({}, {}, 1)
> +---
> +- []
> +...
> +minus_yield({}, {k = 1}, 1)
> +---
> +- []
> +...
> +minus_yield({}, {k = 1}, 0)
> +---
> +- []
> +...
> +minus_yield({k = 1}, {k = 1}, 0)
> +---
> +- []
> +...
> +minus_yield({k1 = 1, k2 = 2}, {k1 = 1, k3 = 3}, 10)
> +---
> +- k2: 2
> +...
> +minus_yield({k1 = 1, k2 = 2}, {k1 = 1, k2 = 2}, 10)
> +---
> +- []
> +...
> +-- Mismatching values are not deleted.
> +minus_yield({k1 = 1}, {k1 = 2}, 10)
> +---
> +- k1: 1
> +...
> +minus_yield({k1 = 1, k2 = 2, k3 = 3}, {k1 = 1, k2 = 222}, 10)
> +---
> +- k3: 3
> +  k2: 2
> +...
> +do                                                                              \
> +    t = {k1 = 1, k2 = 2, k3 = 3, k4 = 4}                                        \
> +    f = fiber.create(function()                                                 \
> +        minus_yield(t, {k2 = 2, k3 = 3, k5 = 5, k4 = 444}, 2)                   \
> +    end)                                                                        \
> +    yield_count = 0                                                             \
> +    while f:status() ~= 'dead' do                                               \
> +        yield_count = yield_count + 1                                           \
> +        fiber.yield()                                                           \
> +    end                                                                         \
> +end
> +---


Why can't you use "csw" of fiber.self() instead? Also it's it reliable 
enough to simply count yields?

Could scheduler skip this fiber at some loop iteration? In other words, 
won't this test be flaky?


> +...
> +yield_count
> +---
> +- 2
> +...
> +t
> +---
> +- k4: 4
> +  k1: 1
> +...
> +-- Yielding table copy.
> +copy_yield = util.table_copy_yield
> +---
> +...
> +copy_yield({}, 1)
> +---
> +- []
> +...
> +copy_yield({k = 1}, 1)
> +---
> +- k: 1
> +...
> +copy_yield({k1 = 1, k2 = 2}, 1)
> +---
> +- k1: 1
> +  k2: 2
> +...
> +do                                                                              \
> +    t = {k1 = 1, k2 = 2, k3 = 3, k4 = 4}                                        \
> +    res = nil                                                                   \
> +    f = fiber.create(function()                                                 \
> +        res = copy_yield(t, 2)                                                  \
> +    end)                                                                        \
> +    yield_count = 0                                                             \
> +    while f:status() ~= 'dead' do                                               \
> +        yield_count = yield_count + 1                                           \
> +        fiber.yield()                                                           \
> +    end                                                                         \
> +end
> +---
> +...
> +yield_count
> +---
> +- 2
> +...
> +t
> +---
> +- k3: 3
> +  k4: 4
> +  k1: 1
> +  k2: 2
> +...
> +res
> +---
> +- k3: 3
> +  k4: 4
> +  k1: 1
> +  k2: 2
> +...
> +t ~= res
> +---
> +- true
> +...
> diff --git a/test/unit/util.test.lua b/test/unit/util.test.lua
> index 5f39e06..4d6cbe9 100644
> --- a/test/unit/util.test.lua
> +++ b/test/unit/util.test.lua
> @@ -27,3 +27,52 @@ fib = util.reloadable_fiber_create('Worker_name', fake_M, 'reloadable_function')
>   while not test_run:grep_log('default', 'module is reloaded, restarting') do fiber.sleep(0.01) end
>   test_run:grep_log('default', 'reloadable_function has been started', 1000)
>   fib:cancel()
> +
> +-- Yielding table minus.
> +minus_yield = util.table_minus_yield
> +minus_yield({}, {}, 1)
> +minus_yield({}, {k = 1}, 1)
> +minus_yield({}, {k = 1}, 0)
> +minus_yield({k = 1}, {k = 1}, 0)
> +minus_yield({k1 = 1, k2 = 2}, {k1 = 1, k3 = 3}, 10)
> +minus_yield({k1 = 1, k2 = 2}, {k1 = 1, k2 = 2}, 10)
> +-- Mismatching values are not deleted.
> +minus_yield({k1 = 1}, {k1 = 2}, 10)
> +minus_yield({k1 = 1, k2 = 2, k3 = 3}, {k1 = 1, k2 = 222}, 10)
> +
> +do                                                                              \
> +    t = {k1 = 1, k2 = 2, k3 = 3, k4 = 4}                                        \
> +    f = fiber.create(function()                                                 \
> +        minus_yield(t, {k2 = 2, k3 = 3, k5 = 5, k4 = 444}, 2)                   \
> +    end)                                                                        \
> +    yield_count = 0                                                             \
> +    while f:status() ~= 'dead' do                                               \
> +        yield_count = yield_count + 1                                           \
> +        fiber.yield()                                                           \
> +    end                                                                         \
> +end
> +yield_count
> +t
> +
> +-- Yielding table copy.
> +copy_yield = util.table_copy_yield
> +copy_yield({}, 1)
> +copy_yield({k = 1}, 1)
> +copy_yield({k1 = 1, k2 = 2}, 1)
> +
> +do                                                                              \
> +    t = {k1 = 1, k2 = 2, k3 = 3, k4 = 4}                                        \
> +    res = nil                                                                   \
> +    f = fiber.create(function()                                                 \
> +        res = copy_yield(t, 2)                                                  \
> +    end)                                                                        \
> +    yield_count = 0                                                             \
> +    while f:status() ~= 'dead' do                                               \
> +        yield_count = yield_count + 1                                           \
> +        fiber.yield()                                                           \
> +    end                                                                         \
> +end
> +yield_count
> +t
> +res
> +t ~= res
> diff --git a/vshard/util.lua b/vshard/util.lua
> index d3b4e67..2362607 100644
> --- a/vshard/util.lua
> +++ b/vshard/util.lua
> @@ -153,6 +153,44 @@ local function version_is_at_least(major_need, middle_need, minor_need)
>       return minor >= minor_need
>   end
>   
> +--
> +-- Copy @a src table. Fiber yields every @a interval keys copied.
> +--
> +local function table_copy_yield(src, interval)
> +    local res = {}
> +    -- Time-To-Yield.
> +    local tty = interval
> +    for k, v in pairs(src) do
> +        res[k] = v
> +        tty = tty - 1
> +        if tty <= 0 then
> +            fiber.yield()
> +            tty = interval
> +        end
> +    end
> +    return res
> +end
> +
> +--
> +-- Remove @a src keys from @a dst if their values match. Fiber yields every
> +-- @a interval iterations.
> +--
> +local function table_minus_yield(dst, src, interval)
> +    -- Time-To-Yield.
> +    local tty = interval
> +    for k, srcv in pairs(src) do
> +        if dst[k] == srcv then
> +            dst[k] = nil
> +        end
> +        tty = tty - 1
> +        if tty <= 0 then
> +            fiber.yield()
> +            tty = interval
> +        end
> +    end
> +    return dst
> +end
> +
>   return {
>       tuple_extract_key = tuple_extract_key,
>       reloadable_fiber_create = reloadable_fiber_create,
> @@ -160,4 +198,6 @@ return {
>       async_task = async_task,
>       internal = M,
>       version_is_at_least = version_is_at_least,
> +    table_copy_yield = table_copy_yield,
> +    table_minus_yield = table_minus_yield,
>   }