[Tarantool-patches] Fwd: Re[2]: [PATCH 3/3] tuple: use calloc for service truncation tuples
Ilya Kosarev
i.kosarev at tarantool.org
Fri Jan 10 14:45:04 MSK 2020
Thanks for the review!
Well, yes, i first thought that it is something we don’t want to fix.
However, then i decided to try it in the present way, as far as i
didn't see all the trouble coming. Now i see it won't work this way.
Nevertheless i think this issue is quite uncomfortable for user. Sent
v2 of the patchset with approach inspired by your idea. It looks much
better, however, still not sure if it is worth implementing.
>Четверг, 19 декабря 2019, 3:31 +03:00 от Vladislav Shpilevoy < v.shpilevoy at tarantool.org >:
>
>Thanks for the patch!
>
>See 3 comments below.
>
>On 13/12/2019 08:05, Ilya Kosarev wrote:
>> Trying to perform space:truncate() while reaching memtx_memory limit we
>> could experience slab allocator failure on allocation for service tuple
>> being upserted into service space to keep record of truncations. This
>> behavior seems to be quite surprising for users. Now we are using
>> calloc() to allocate tuples in BOX_TRUNCATE_ID space.
>>
>> Closes: #3807
>> ---
>> src/box/memtx_engine.c | 50 ++++++++++++++++++++++++++++--------------
>> src/box/memtx_engine.h | 2 +-
>> src/box/memtx_space.c | 20 ++++++++++++-----
>> src/box/tuple.c | 16 ++++++++++----
>> src/box/tuple.h | 2 +-
>> src/box/tuple_format.c | 1 +
>> src/box/tuple_format.h | 10 ++++++++-
>> src/box/vy_stmt.c | 3 ++-
>> 8 files changed, 74 insertions(+), 30 deletions(-)
>>
>> diff --git a/src/box/memtx_engine.c b/src/box/memtx_engine.c
>> index 23ccc4703fe..59148059f2b 100644
>> --- a/src/box/memtx_engine.c
>> +++ b/src/box/memtx_engine.c
>> @@ -1113,7 +1113,7 @@ memtx_leave_delayed_free_mode(struct memtx_engine *memtx)
>> }
>>
>> struct tuple *
>> -memtx_tuple_new(struct tuple_format *format, const char *data, const char *end)
>> +memtx_tuple_new(struct tuple_format *format, const char *data, const char *end, bool use_calloc)
>
>1. Oh. No. Please. The whole point of format vtable is to avoid that.
>
>> {
>> struct memtx_engine *memtx = (struct memtx_engine *)format->engine;
>> assert(mp_typeof(*data) == MP_ARRAY);
>> @@ -1139,15 +1139,27 @@ memtx_tuple_new(struct tuple_format *format, const char *data, const char *end)
>> }
>>
>> struct memtx_tuple *memtx_tuple;
>> - while ((memtx_tuple = smalloc(&memtx->alloc, total)) == NULL) {
>> - bool stop;
>> - memtx_engine_run_gc(memtx, &stop);
>> - if (stop)
>> - break;
>> - }
>> - if (memtx_tuple == NULL) {
>> - diag_set(OutOfMemory, total, "slab allocator", "memtx_tuple");
>> - goto end;
>> + if (use_calloc) {
>> + memtx_tuple = calloc(1, total);
>> + if (memtx_tuple == NULL) {
>> + diag_set(OutOfMemory, total, "malloc",
>> + "memtx_tuple");
>> + goto end;
>> + }
>> + format->is_malloced = true;
>
>2. Sorry, we can't change format here. The only reason why format
>is not const in that function is because we need increment its
>reference counter. A tuple can't change its own format. Especially
>in such a hot path.
>
>> + } else {
>> + while ((memtx_tuple = smalloc(&memtx->alloc,
>> + total)) == NULL) {
>> + bool stop;
>> + memtx_engine_run_gc(memtx, &stop);
>> + if (stop)
>> + break;
>> + }
>> + if (memtx_tuple == NULL) {
>> + diag_set(OutOfMemory, total, "slab allocator",
>> + "memtx_tuple");
>> + goto end;
>> + }
>> }
>> tuple = &memtx_tuple->base;
>> tuple->refs = 0;
>> @@ -1177,16 +1189,20 @@ memtx_tuple_delete(struct tuple_format *format, struct tuple *tuple)
>> struct memtx_engine *memtx = (struct memtx_engine *)format->engine;
>> say_debug("%s(%p)", __func__, tuple);
>> assert(tuple->refs == 0);
>> - tuple_format_unref(format);
>> struct memtx_tuple *memtx_tuple =
>> container_of(tuple, struct memtx_tuple, base);
>> size_t total = tuple_size(tuple) + offsetof(struct memtx_tuple, base);
>> - if (memtx->alloc.free_mode != SMALL_DELAYED_FREE ||
>> - memtx_tuple->version == memtx->snapshot_version ||
>> - format->is_temporary)
>> - smfree(&memtx->alloc, memtx_tuple, total);
>> - else
>> - smfree_delayed(&memtx->alloc, memtx_tuple, total);
>> + if (format->is_malloced) {
>> + free(memtx_tuple);
>
>3. There is a certain purpose for these free_mode, version, blah
>blah. These attributes create a read view of the whole memtx engine
>to make a snapshot, but do not stop new requests. Tuples are not
>deleted during snapshot.
>
>Having ignored the free mode you get this:
>
>====================================================================
>
> box.cfg{}
> errinj = box.error.injection
> fiber = require('fiber')
>
> s = box.schema.create_space('test')
> pk = s:create_index('pk')
> s:truncate()
> s:replace{1}
> box.error.injection.set('ERRINJ_SNAP_WRITE_DELAY', true)
> f = fiber.create(box.snapshot)
> box.space._truncate:delete{s.id}
>
>-- The code below improves reproducibility. It creates and
>-- deletes several tuples to unref the blessed tuple
>-- (tuple_bless), rewrite some recently freed heap chunks.
>
> s:get{1}
> collectgarbage('collect')
> s:replace{1}
> s:get{1}
> collectgarbage('collect')
> s:replace{1}
> s:get{1}
> collectgarbage('collect')
> s:replace{1}
> s:get{1}
> collectgarbage('collect')
>
>--
>
> box.error.injection.set('ERRINJ_SNAP_WRITE_DELAY', false)
>
> tarantool> Process 94390 stopped
> * thread #2, name = 'snapshot', stop reason = EXC_BAD_ACCESS (code=2, address=0x105481000)
> frame #0: 0x00007fff5a964ce9 libsystem_platform.dylib`_platform_memmove$VARIANT$Haswell + 41
> libsystem_platform.dylib`_platform_memmove$VARIANT$Haswell:
> -> 0x7fff5a964ce9 <+41>: rep movsb (%rsi), %es:(%rdi)
> 0x7fff5a964ceb <+43>: popq %rbp
> 0x7fff5a964cec <+44>: retq
> 0x7fff5a964ced <+45>: cmpq %rdi, %rsi
> Target 0: (tarantool) stopped.
> (lldb) bt
> * thread #2, name = 'snapshot', stop reason = EXC_BAD_ACCESS (code=2, address=0x105481000)
> * frame #0: 0x00007fff5a964ce9 libsystem_platform.dylib`_platform_memmove$VARIANT$Haswell + 41
> frame #1: 0x00000001003f56ba tarantool`obuf_dup(buf=0x000000010f0ff8b0, data=0x0000000105157aa6, size=85071264) at obuf.c:161:2
> frame #2: 0x00000001003634e8 tarantool`xlog_write_row(log=0x000000010f0ff208, packet=0x000000010f0ff0d8) at xlog.c:1320:7
> frame #3: 0x0000000100038aef tarantool`checkpoint_write_row(l=0x000000010f0ff208, row=0x000000010f0ff0d8) at memtx_engine.c:431:20
> frame #4: 0x0000000100038a2e tarantool`checkpoint_write_tuple(l=0x000000010f0ff208, space_id=330, group_id=0, data="", size=85071264) at memtx_engine.c:459:9
> frame #5: 0x0000000100038811 tarantool`checkpoint_f(ap=0x000000010f000278) at memtx_engine.c:603:8
> frame #6: 0x0000000100005e5a tarantool`fiber_cxx_invoke(f=(tarantool`checkpoint_f at memtx_engine.c:577), ap=0x000000010f000278)(__va_list_tag*), __va_list_tag*) at fiber.h:762:10
> frame #7: 0x000000010018168b tarantool`fiber_loop(data=0x0000000000000000) at fiber.c:830:18
> frame #8: 0x00000001004165e7 tarantool`coro_init at coro.c:110:3
>
>====================================================================
>
>Snapshoting means that you can't solve the issue on the format
>level, or tuple level. You need to patch the engine level (IMO).
>
>Honestly, I thought about this issue for quite a long time already,
>and I don't have a plan how to fix it. All ways look bad. All of them
>assume special patching of _truncate space insertion and crutches for
>deletion. For me the most promising way was to introduce an analogue
>of vy_quota_force_use() somehow, for _truncate, and use it in a
>before_replace trigger of _truncate. Forced use of quota would allow
>to temporary overflow the memory limit. But it won't fix deletion.
>Maybe the key is in introduction of quota overuse for deletions. I
>don't know.
>
>Personally, I don't think the issue is worth fixing at all. If a
>user wants to delete/truncate, he can increase memtx memory, do
>cleanup, and decrease it back.
--
Ilya Kosarev
----------------------------------------------------------------------
--
Ilya Kosarev
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