diff options
-rw-r--r-- | erts/emulator/beam/erl_db_hash.c | 47 | ||||
-rw-r--r-- | erts/emulator/beam/erl_db_hash.h | 3 |
2 files changed, 39 insertions, 11 deletions
diff --git a/erts/emulator/beam/erl_db_hash.c b/erts/emulator/beam/erl_db_hash.c index 0302b9f1a1..bc2db86b3b 100644 --- a/erts/emulator/beam/erl_db_hash.c +++ b/erts/emulator/beam/erl_db_hash.c @@ -93,11 +93,9 @@ erts_flxctr_dec_read_centralized(&(DB)->common.counters, ERTS_DB_TABLE_NITEMS_COUNTER_ID) #define RESET_NITEMS(DB) \ erts_flxctr_reset(&(DB)->common.counters, ERTS_DB_TABLE_NITEMS_COUNTER_ID) -/* - * The following symbols can be manipulated to "tune" the linear hash array - */ + #define GROW_LIMIT(NACTIVE) ((NACTIVE)*1) -#define SHRINK_LIMIT(NACTIVE) ((NACTIVE) / 2) +#define SHRINK_LIMIT(TB) erts_atomic_read_nob(&(TB)->shrink_limit) /* ** We want the first mandatory segment to be small (to reduce minimal footprint) @@ -476,10 +474,8 @@ db_finalize_dbterm_hash(int cret, DbUpdateHandle* handle); static ERTS_INLINE void try_shrink(DbTableHash* tb) { - int nactive = NACTIVE(tb); int nitems = NITEMS(tb); - if (nactive > FIRST_SEGSZ && nitems < SHRINK_LIMIT(nactive) - && !IS_FIXED(tb)) { + if (nitems < SHRINK_LIMIT(tb) && !IS_FIXED(tb)) { shrink(tb, nitems); } } @@ -690,6 +686,7 @@ int db_create_hash(Process *p, DbTable *tbl) erts_atomic_init_nob(&tb->szm, FIRST_SEGSZ_MASK); erts_atomic_init_nob(&tb->nactive, FIRST_SEGSZ); + erts_atomic_init_nob(&tb->shrink_limit, 0); erts_atomic_init_nob(&tb->fixdel, (erts_aint_t)NULL); erts_atomic_init_nob(&tb->segtab, (erts_aint_t)NULL); SET_SEGTAB(tb, tb->first_segtab); @@ -2669,6 +2666,34 @@ static struct ext_segtab* alloc_ext_segtab(DbTableHash* tb, unsigned seg_ix) return est; } +static void calc_shrink_limit(DbTableHash* tb) +{ + erts_aint_t shrink_limit; + + if (tb->nslots >= (FIRST_SEGSZ + 2*EXT_SEGSZ)) { + /* + * Start shrink when we can remove one extra segment + * and still remain below 50% load. + */ + shrink_limit = (tb->nslots - EXT_SEGSZ) / 2; + } + else { + /* + * But don't shrink below two segments. + * Why? In order to have chance of getting rid of the last extra segment, + * and rehash it into the first small segment, we either have to start + * early and do speculative joining of buckets or we have to join a lot + * of buckets during each delete-op. + * + * Instead keep segment #2 once allocated. I also think it's a good bet + * a shrinking large table will grow large again. + */ + shrink_limit = 0; + } + erts_atomic_set_nob(&tb->shrink_limit, shrink_limit); +} + + /* Extend table with one new segment */ static void alloc_seg(DbTableHash *tb) @@ -2696,6 +2721,8 @@ static void alloc_seg(DbTableHash *tb) } #endif tb->nslots += EXT_SEGSZ; + + calc_shrink_limit(tb); } static void dealloc_ext_segtab(void* lop_data) @@ -2789,6 +2816,7 @@ static int remove_seg(DbTableHash *tb, int free_records, if (seg_ix < tb->nsegs) SEGTAB(tb)[seg_ix] = NULL; #endif + calc_shrink_limit(tb); return nrecords; } @@ -3003,7 +3031,7 @@ static void shrink(DbTableHash* tb, int nitems) if (!begin_resizing(tb)) return; /* already in progress */ nactive = NACTIVE(tb); - if (!(nactive > FIRST_SEGSZ && nitems < SHRINK_LIMIT(nactive))) { + if (!(nitems < SHRINK_LIMIT(tb))) { goto abort; /* already done (race) */ } src_ix = nactive - 1; @@ -3062,8 +3090,7 @@ static void shrink(DbTableHash* tb, int nitems) ds_ops.segp = NULL; } - } while (--loop_limit - && nactive > FIRST_SEGSZ && nitems < SHRINK_LIMIT(nactive)); + } while (--loop_limit && nitems < SHRINK_LIMIT(tb)); return; abort: diff --git a/erts/emulator/beam/erl_db_hash.h b/erts/emulator/beam/erl_db_hash.h index eae5537ba4..ecd2ca74a1 100644 --- a/erts/emulator/beam/erl_db_hash.h +++ b/erts/emulator/beam/erl_db_hash.h @@ -63,9 +63,10 @@ typedef struct db_table_hash_fine_locks { typedef struct db_table_hash { DbTableCommon common; - /* SMP: szm and nactive are write-protected by is_resizing or table write lock */ + /* szm, nactive, shrink_limit are write-protected by is_resizing or table write lock */ erts_atomic_t szm; /* current size mask. */ erts_atomic_t nactive; /* Number of "active" slots */ + erts_atomic_t shrink_limit; /* Shrink table when fewer objects than this */ erts_atomic_t segtab; /* The segment table (struct segment**) */ struct segment* first_segtab[1]; |