[PATCH v3 7/7] Add merger for tuple streams (Lua part)
Alexander Turenko
alexander.turenko at tarantool.org
Wed May 8 01:14:43 MSK 2019
Thanks!
I'll send 4th version of the patchset.
WBR, Alexander Turenko.
On Tue, Apr 30, 2019 at 08:37:24PM +0300, Vladimir Davydov wrote:
> On Wed, Apr 10, 2019 at 06:21:25PM +0300, Alexander Turenko wrote:
> > A merger is a special kind of a source, which is created from a key_def
> > object and a set of sources. It performs a kind of the merge sort:
> > chooses a source with a minimal / maximal tuple on each step, consumes
> > a tuple from this source and repeats. The API to create a merger is the
> > following:
> >
> > ```lua
> > local ctx = merger.context.new(key_def.new(<...>))
>
> Discussed verbally, agreed that a performance gain from using
> merger.context is somewhat dubious. It's compelling to drop it
> altogether and pass key_def to merger.new directly, creating
> a format every time (we can reuse formats if necessary in future).
> Alexander will think about it.
Okay. Removed.
I'll suggest to cache a key_def instead of a merge context in
tarantool-merger-examples.
>
> Other than that the API and the patch looks good to me.
>
> See a few minor comments below.
>
> > local sources = {<...>}
> > local merger_inst = merger.new(ctx, sources, {
> > -- Ascending (false) or descending (true) order.
> > -- Default is ascending.
> > reverse = <boolean> or <nil>,
> > })
> > ```
>
> > diff --git a/src/box/lua/merger.c b/src/box/lua/merger.c
> > new file mode 100644
> > index 000000000..ebe60bc8d
> > --- /dev/null
> > +++ b/src/box/lua/merger.c
> > @@ -0,0 +1,1184 @@
>
> > +static uint32_t merger_source_type_id = 0;
> > +static uint32_t merger_context_type_id = 0;
> > +static uint32_t ibuf_type_id = 0;
>
> We typically use upper case for naming variables storing Lua type ids,
> e.g. CTID_STRUCT_TUPLE_REF.
Changed to CTID_STRUCT_IBUF and CTID_STRUCT_MERGE_SOURCE_REF.
>
> > +static int
> > +lbox_merger_source_gc(struct lua_State *L)
> > +{
> > + struct merger_source *source;
> > + if ((source = luaT_check_merger_source(L, 1)) == NULL)
> > + return 0;
>
> Is it actually possible?
No. It was carried from the original shard/driver.c, but tarantool's
code don't perform such checks. Replaced with assert.
>
> > + merger_source_unref(source);
> > + return 0;
> > +}
>
> > +static struct merger_source **
> > +luaT_merger_new_parse_sources(struct lua_State *L, int idx,
> > + uint32_t *sources_count_ptr)
> > +{
> > + /* Allocate sources array. */
> > + uint32_t sources_count = lua_objlen(L, idx);
> > + const ssize_t sources_size =
> > + sources_count * sizeof(struct merger_source *);
> > + struct merger_source **sources =
> > + (struct merger_source **) malloc(sources_size);
>
> Pointless type conversion.
Removed. Also changed the order from `count * sizeof(...)` to
`sizeof(...) * count` where we allocate arrays to do the arithmetic in
size_t. There is no real reason, just to do things in the right way.
Also fixed the place (it is this function) where I mistakely save an
array size into a ssize_t (signed) variable.
>
> > + if (sources == NULL) {
> > + diag_set(OutOfMemory, sources_size, "malloc", "sources");
> > + return NULL;
> > + }
> > +
> > + /* Save all sources. */
> > + for (uint32_t i = 0; i < sources_count; ++i) {
> > + lua_pushinteger(L, i + 1);
> > + lua_gettable(L, idx);
> > +
> > + /* Extract a source from a Lua stack. */
> > + struct merger_source *source = luaT_check_merger_source(L, -1);
> > + if (source == NULL) {
> > + free(sources);
> > + diag_set(IllegalParams,
> > + "Unknown source type at index %d", i + 1);
> > + return NULL;
> > + }
> > + sources[i] = source;
> > + }
> > + lua_pop(L, sources_count);
> > +
> > + *sources_count_ptr = sources_count;
>
> source_count
Changed all *_count names in that way and also changed all *_cnt to
*_count.
>
> > +struct merger_source_buffer {
> > + struct merger_source base;
> > + /*
> > + * A reference to a Lua iterator to fetch a next chunk of
> > + * tuples.
> > + */
> > + struct luaL_iterator *fetch_it;
> > + /*
> > + * A reference a buffer with a current chunk of tuples.
>
> A reference to a buffer storing the current chunk of tuples.
I don't get why 'THE current chunk', but changed as you suggested
anyway.
>
> > + * It is needed to prevent LuaJIT from collecting the
> > + * buffer while the source consider it as the current
> > + * one.
> > + */
> > + int ref;
> > + /*
> > + * A buffer with a current chunk of tuples.
> > + */
> > + struct ibuf *buf;
> > + /*
> > + * A merger stops before end of a buffer when it is not
> > + * the last merger in the chain.
> > + */
> > + size_t remaining_tuples_cnt;
>
> Please rename to remaining_tuple_count.
Done.
>
> > +static int
> > +luaL_merger_source_buffer_fetch(struct merger_source_buffer *source)
> > +{
> > + struct lua_State *L = fiber()->storage.lua.stack;
> > + int nresult = luaL_iterator_next(L, source->fetch_it);
> > +
> > + /* Handle a Lua error in a gen function. */
> > + if (nresult == -1)
> > + return -1;
> > +
> > + /* No more data: do nothing. */
> > + if (nresult == 0)
> > + return 0;
> > +
> > + /* Handle incorrect results count. */
> > + if (nresult != 2) {
> > + diag_set(IllegalParams, "Expected <state>, <buffer>, got %d "
> > + "return values", nresult);
> > + return -1;
> > + }
> > +
> > + /* Set a new buffer as the current chunk. */
> > + if (source->ref > 0)
> > + luaL_unref(L, LUA_REGISTRYINDEX, source->ref);
> > + lua_pushvalue(L, -nresult + 1); /* Popped by luaL_ref(). */
> > + source->ref = luaL_ref(L, LUA_REGISTRYINDEX);
> > + source->buf = luaT_check_ibuf(L, -1);
> > + assert(source->buf != NULL);
>
> | tarantool> m = merger.new(c, {merger.new_buffer_source(box.space._space:pairs())})
> | ---
> | ...
> |
> | tarantool> m:select()
> | luaL_merger_source_buffer_fetch: Assertion `source->buf != NULL' failed.
>
> Please fail gracefully in this case.
Nice catch. Fixed. Added 'bad_chunks' test cases.
>
> > + lua_pop(L, nresult);
> > +
> > + /* Update remaining_tuples_cnt and skip the header. */
> > + if (decode_header(source->buf, &source->remaining_tuples_cnt) != 0) {
> > + diag_set(IllegalParams, "Invalid merger source %p",
> > + &source->base);
> > + return -1;
> > + }
> > + return 1;
> > +}
> > +
> > +/* Virtual methods */
> > +
> > +static void
> > +luaL_merger_source_buffer_delete(struct merger_source *base)
> > +{
> > + struct merger_source_buffer *source = container_of(base,
> > + struct merger_source_buffer, base);
> > +
> > + assert(source->fetch_it != NULL);
> > + luaL_iterator_delete(source->fetch_it);
> > + if (source->ref > 0)
> > + luaL_unref(tarantool_L, LUA_REGISTRYINDEX, source->ref);
> > +
> > + free(source);
> > +}
> > +
> > +static int
> > +luaL_merger_source_buffer_next(struct merger_source *base,
> > + box_tuple_format_t *format,
> > + struct tuple **out)
> > +{
> > + struct merger_source_buffer *source = container_of(base,
> > + struct merger_source_buffer, base);
> > +
> > + /*
> > + * Handle the case when all data were processed: ask a
> > + * next chunk until a non-empty chunk is received or a
> > + * chunks iterator ends.
> > + */
> > + while (source->remaining_tuples_cnt == 0) {
> > + int rc = luaL_merger_source_buffer_fetch(source);
> > + if (rc < 0)
> > + return -1;
> > + if (rc == 0) {
> > + *out = NULL;
> > + return 0;
> > + }
> > + }
> > + if (ibuf_used(source->buf) == 0) {
> > + diag_set(IllegalParams, "Unexpected msgpack buffer end");
> > + return -1;
> > + }
> > + const char *tuple_beg = source->buf->rpos;
> > + const char *tuple_end = tuple_beg;
> > + /*
> > + * mp_next() is faster then mp_check(), but can read bytes
> > + * outside of the buffer and so can cause segmentation
> > + * faults or an incorrect result.
> > + *
> > + * We check buffer boundaries after the mp_next() call and
> > + * throw an error when the boundaries are violated, but it
> > + * does not save us from possible segmentation faults.
> > + *
> > + * It is in a user responsibility to provide valid
> > + * msgpack.
>
> Ugh, I'd check the buffer with mp_check anyway. Would probably provide
> an option to skip the check if required ('unchecked'). Not sure if it's
> really necessary though.
Okay.
>
> > + */
> > + mp_next(&tuple_end);
> > + --source->remaining_tuples_cnt;
> > + if (tuple_end > source->buf->wpos) {
> > + diag_set(IllegalParams, "Unexpected msgpack buffer end");
> > + return -1;
> > + }
> > + source->buf->rpos = (char *) tuple_end;
> > + if (format == NULL)
> > + format = box_tuple_format_default();
>
> I'd pass tuple_format_runtime explicitly to the ->next callback.
> Special-casing NULL is kinda ugly.
NULL value for a format has the special meaning for source->next(): it
does not matter for a caller in which format a resulting tuple will be
(see the comment for next() in struct merge_source_vtab). It is not
always means that a tuple will be in the runtime format: say, for a
tuple source it means that it will return tuples in its original format.
The same is applicable for a table source when a chunk contains tuples
(not Lua tables).
This does not matter much for a buffer source, but it is the part of a
source contract in general. I'll leave it as is if you don't mind.
>
> > + struct tuple *tuple = box_tuple_new(format, tuple_beg, tuple_end);
> > + if (tuple == NULL)
> > + return -1;
> > +
> > + box_tuple_ref(tuple);
> > + *out = tuple;
> > + return 0;
> > +}
>
> > +static int
> > +encode_result_buffer(struct lua_State *L, struct merger_source *source,
> > + struct ibuf *obuf, uint32_t limit)
>
> Better rename 'obuf' to 'out' or 'buf' or something - we have struct
> obuf so 'struct ibuf *obuf' looks misleading.
We use 'buf' where reading from it, so I would use some another name
when writing. 'out' looks more appropriate for a scalar / pointer value
we'll replace in a function. I'll use 'output_buffer' here and in other
such places in C and Lua if you don't mind.
>
> > +{
> > + uint32_t result_len = 0;
> > + uint32_t result_len_offset = 4;
> > +
> > + /*
> > + * Reserve maximum size for the array around resulting
> > + * tuples to set it later.
> > + */
> > + encode_header(obuf, UINT32_MAX);
> > +
> > + /* Fetch, merge and copy tuples to the buffer. */
> > + struct tuple *tuple;
> > + int rc = 0;
> > + while (result_len < limit && (rc =
> > + source->vtab->next(source, NULL, &tuple)) == 0 &&
> > + tuple != NULL) {
> > + uint32_t bsize = tuple->bsize;
> > + ibuf_reserve(obuf, bsize);
> > + memcpy(obuf->wpos, tuple_data(tuple), bsize);
> > + obuf->wpos += bsize;
> > + result_len_offset += bsize;
> > + ++result_len;
> > +
> > + /* The received tuple is not more needed. */
> > + box_tuple_unref(tuple);
> > + }
> > +
> > + if (rc != 0)
> > + return luaT_error(L);
> > +
> > + /* Write the real array size. */
> > + mp_store_u32(obuf->wpos - result_len_offset, result_len);
> > +
> > + return 0;
> > +}
>
> > +static int
> > +lbox_merger_source_select(struct lua_State *L)
> > +{
> > + struct merger_source *source;
> > + int top = lua_gettop(L);
> > + bool ok = (top == 1 || top == 2) &&
> > + /* Merger source. */
> > + (source = luaT_check_merger_source(L, 1)) != NULL &&
> > + /* Opts. */
> > + (lua_isnoneornil(L, 2) == 1 || lua_istable(L, 2) == 1);
> > + if (!ok)
> > + return lbox_merger_source_select_usage(L, NULL);
> > +
> > + uint32_t limit = 0xFFFFFFFF;
>
> Hmm, UINT32_MAX?
Okay, changed.
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