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Reduce encoder memory allocations #301

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Merged
nickva merged 1 commit into from
Jun 15, 2026
Merged

Reduce encoder memory allocations #301

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17 changes: 15 additions & 2 deletions c_src/encoder.c
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,12 @@

#define BIN_INC_SIZE 2048

// When we flush output buffer to an iolist double the next chunk size so a
// large doc is emitted in O(log n) segments. But we also limit it at 64KB
// size. This should reduce total number of memory allocations (those can
// become a bottleneck).
#define MAX_CHUNK_SIZE (64 * 1024)

#define MIN(X, Y) ((X) < (Y) ? (X) : (Y))

#define SMALL_TERMSTACK_SIZE 16
Expand Down Expand Up @@ -51,6 +57,7 @@ typedef struct {

ErlNifBinary buffer;
int have_buffer;
size_t chunk_size;

unsigned char* p;
size_t i;
Expand Down Expand Up @@ -169,8 +176,9 @@ enc_new(ErlNifEnv* env)
e->atoms = st;
e->bytes_per_red = DEFAULT_BYTES_PER_REDUCTION;
e->iolist = enif_make_list(env, 0);
e->chunk_size = BIN_INC_SIZE;

if(!enif_alloc_binary(BIN_INC_SIZE, &e->buffer)) {
if(!enif_alloc_binary(e->chunk_size, &e->buffer)) {
enif_release_resource(e);
return NULL;
}
Expand Down Expand Up @@ -246,6 +254,11 @@ enc_flush(Encoder* e)
e->iolist = enif_make_list_cell(e->env, bin, e->iolist);
e->iosize += e->i;

// Grow the next chunk geometrically so large outputs flush O(log n) times.
if(e->chunk_size < MAX_CHUNK_SIZE) {
e->chunk_size <<= 1;
}

return 1;
}

Expand All @@ -268,7 +281,7 @@ enc_ensure(Encoder* e, size_t req)
}
}

for(new_size = BIN_INC_SIZE; new_size < req; new_size <<= 1);
for(new_size = e->chunk_size; new_size < req; new_size <<= 1);

if(!enif_alloc_binary(new_size, &e->buffer)) {
return 0;
Expand Down
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