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Merged
rtjohnso merged 2 commits into from
Apr 2, 2026
Merged

Dynamically size btree scratch in order to shrink memtable contexts #661

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e6e2406
make btree scratch dynamically sized in order to shrink memtable cont…
rtjohnso Apr 2, 2026
11c0250
fix tests
rtjohnso Apr 2, 2026
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13 changes: 7 additions & 6 deletions src/btree.h
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Original file line number Diff line number Diff line change
Expand Up @@ -93,18 +93,19 @@ typedef struct btree_node {
} btree_node;

typedef struct {
char merged_data[MAX_INLINE_MESSAGE_SIZE(MAX_PAGE_SIZE)];
} scratch_btree_add_tuple;

typedef struct {
char scratch_node[MAX_PAGE_SIZE];
char scratch_node[1]; // Actual size is btree_scratch_size(cfg)
} scratch_btree_defragment_node;

typedef struct { // Note: not a union
scratch_btree_add_tuple add_tuple;
scratch_btree_defragment_node defragment_node;
} PLATFORM_CACHELINE_ALIGNED btree_scratch;

static inline uint64
btree_scratch_size(const btree_config *cfg)
{
return cache_config_page_size(cfg->cache_cfg);
}

/*
* *************************************************************************
* BTree pivot data: Disk-resident structure
Expand Down
34 changes: 30 additions & 4 deletions src/memtable.c
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Expand Up @@ -207,6 +207,13 @@ memtable_add_tuple(memtable_context *ctxt)
ctxt->is_empty = FALSE;
}

static btree_scratch *
get_btree_scratch(memtable_context *ctxt, uint64 tid)
{
return (btree_scratch *)(ctxt->btree_scratches
+ tid * ctxt->btree_scratch_sz);
}

platform_status
memtable_insert(memtable_context *ctxt,
memtable *mt,
Expand All @@ -218,10 +225,11 @@ memtable_insert(memtable_context *ctxt,
const threadid tid = platform_get_tid();
bool32 was_unique;

platform_status rc = btree_insert(ctxt->cc,
btree_scratch *scratch = get_btree_scratch(ctxt, tid);
platform_status rc = btree_insert(ctxt->cc,
ctxt->cfg.btree_cfg,
heap_id,
&ctxt->scratch[tid],
scratch,
mt->root_addr,
&mt->mini,
tuple_key,
Expand Down Expand Up @@ -311,15 +319,31 @@ memtable_context_init(memtable_context *ctxt,
ZERO_CONTENTS(ctxt);
ctxt->cc = cc;
ctxt->cfg = *cfg;
ctxt->hid = hid;

if (MAX_MEMTABLES < cfg->max_memtables) {
platform_error_log("Configured number of memtables (%lu) exceeds max "
"supported memtables (%d)\n",
cfg->max_memtables,
MAX_MEMTABLES);
return STATUS_BAD_PARAM;
}

rc = platform_mutex_init(
&ctxt->incorporation_mutex, platform_get_module_id(), hid);
if (!SUCCESS(rc)) {
return rc;
}
batch_rwlock_init(&ctxt->rwlock);

platform_assert(cfg->max_memtables <= MAX_MEMTABLES);
ctxt->btree_scratch_sz = btree_scratch_size(cfg->btree_cfg);
ctxt->btree_scratches = TYPED_MANUAL_ZALLOC(
hid, ctxt->btree_scratches, ctxt->btree_scratch_sz * MAX_THREADS);
if (ctxt->btree_scratches == NULL) {
platform_mutex_destroy(&ctxt->incorporation_mutex);
return STATUS_NO_MEMORY;
}

batch_rwlock_init(&ctxt->rwlock);

for (uint64 mt_no = 0; mt_no < cfg->max_memtables; mt_no++) {
uint64 generation = mt_no;
Expand Down Expand Up @@ -348,6 +372,8 @@ memtable_context_deinit(memtable_context *ctxt)

platform_mutex_destroy(&ctxt->incorporation_mutex);
batch_rwlock_deinit(&ctxt->rwlock);

platform_free(ctxt->hid, ctxt->btree_scratches);
}

void
Expand Down
10 changes: 6 additions & 4 deletions src/memtable.h
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Expand Up @@ -110,9 +110,10 @@ typedef struct memtable_config {
} memtable_config;

typedef struct memtable_context {
cache *cc;
memtable_config cfg;
task_system *ts;
cache *cc;
memtable_config cfg;
task_system *ts;
platform_heap_id *hid;

process_fn process;
void *process_ctxt;
Expand All @@ -136,7 +137,8 @@ typedef struct memtable_context {
bool32 is_empty;

// Effectively thread local, no locking at all:
btree_scratch scratch[MAX_THREADS];
uint64 btree_scratch_sz;
char *btree_scratches;

memtable mt[MAX_MEMTABLES];
} memtable_context;
Expand Down
19 changes: 13 additions & 6 deletions tests/unit/btree_stress_test.c
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Expand Up @@ -104,7 +104,7 @@ CTEST_DATA(btree_stress)
allocator_config allocator_cfg;
clockcache_config cache_cfg;
task_system_config task_cfg;
btree_scratch test_scratch;
btree_scratch *test_scratch;
btree_config dbtree_cfg;

// To create a heap for io, allocator, cache and splinter
Expand Down Expand Up @@ -152,6 +152,11 @@ CTEST_SETUP(btree_stress)
{
ASSERT_TRUE(FALSE, "Failed to init heap\n");
}

data->test_scratch = TYPED_MANUAL_ZALLOC(
data->hid, data->test_scratch, btree_scratch_size(&data->dbtree_cfg));
ASSERT_NOT_NULL(data->test_scratch);

// Setup execution of concurrent threads
data->io = io_handle_create(&data->io_cfg, data->hid);
if (data->io == NULL
Expand Down Expand Up @@ -217,7 +222,7 @@ CTEST2(btree_stress, iterator_basics)
btree_insert((cache *)&data->cc,
&data->dbtree_cfg,
data->hid,
&data->test_scratch,
data->test_scratch,
root_addr,
&mini,
gen_key(&data->dbtree_cfg, i, keybuf, sizeof(keybuf)),
Expand Down Expand Up @@ -251,11 +256,13 @@ CTEST2(btree_stress, test_random_inserts_concurrent)
insert_thread_params *params = TYPED_ARRAY_ZALLOC(hid, params, nthreads);
platform_thread *threads = TYPED_ARRAY_ZALLOC(hid, threads, nthreads);

uint64 bt_sc_sz = btree_scratch_size(&data->dbtree_cfg);
for (uint64 i = 0; i < nthreads; i++) {
params[i].cc = (cache *)&data->cc;
params[i].cfg = &data->dbtree_cfg;
params[i].hid = data->hid;
params[i].scratch = TYPED_MALLOC(data->hid, params[i].scratch);
params[i].cc = (cache *)&data->cc;
params[i].cfg = &data->dbtree_cfg;
params[i].hid = data->hid;
params[i].scratch =
TYPED_MANUAL_MALLOC(data->hid, params[i].scratch, bt_sc_sz);
params[i].mini = &mini;
params[i].root_addr = root_addr;
params[i].start = i * (nkvs / nthreads);
Expand Down
11 changes: 7 additions & 4 deletions tests/unit/btree_test.c
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Expand Up @@ -66,7 +66,7 @@ CTEST_DATA(btree)
io_config io_cfg;
allocator_config allocator_cfg;
clockcache_config cache_cfg;
btree_scratch test_scratch;
btree_scratch *test_scratch;
btree_config dbtree_cfg;
platform_heap_id hid;
};
Expand Down Expand Up @@ -106,6 +106,9 @@ CTEST_SETUP(btree)
{
ASSERT_TRUE(FALSE, "Failed to parse args\n");
}

data->test_scratch = TYPED_MANUAL_ZALLOC(
data->hid, data->test_scratch, btree_scratch_size(&data->dbtree_cfg));
}

// Optional teardown function for suite, called after every test in suite
Expand All @@ -120,7 +123,7 @@ CTEST_TEARDOWN(btree)
*/
CTEST2(btree, test_leaf_hdr)
{
int rc = leaf_hdr_tests(&data->dbtree_cfg, &data->test_scratch, data->hid);
int rc = leaf_hdr_tests(&data->dbtree_cfg, data->test_scratch, data->hid);
ASSERT_EQUAL(0, rc);
}

Expand All @@ -138,7 +141,7 @@ CTEST2(btree, test_leaf_hdr_search)
*/
CTEST2(btree, test_index_hdr)
{
int rc = index_hdr_tests(&data->dbtree_cfg, &data->test_scratch, data->hid);
int rc = index_hdr_tests(&data->dbtree_cfg, data->test_scratch, data->hid);
ASSERT_EQUAL(0, rc);
}

Expand All @@ -158,7 +161,7 @@ CTEST2(btree, test_leaf_split)
{
for (int nkvs = 2; nkvs < 100; nkvs++) {
int rc = leaf_split_tests(
&data->dbtree_cfg, &data->test_scratch, nkvs, data->hid);
&data->dbtree_cfg, data->test_scratch, nkvs, data->hid);
ASSERT_EQUAL(0, rc);
}
}
Expand Down
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