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mdbx: minor refine/clarify estimation internals.

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This commit is contained in:
Leo Yuriev 2019-03-06 16:45:49 +03:00
parent 501eb8c6ad
commit 73f8839a97
1 changed files with 49 additions and 47 deletions
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92
src/mdbx.c
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@ -13180,78 +13180,79 @@ struct diff_result {
int root_nkeys; int root_nkeys;
}; };
static int cursor_diff(const MDBX_cursor *const __restrict first, /* calculates: r = x - y */
const MDBX_cursor *const __restrict last, __hot static int cursor_diff(const MDBX_cursor *const __restrict x,
struct diff_result *const __restrict dr) { const MDBX_cursor *const __restrict y,
dr->root_nkeys = 0; struct diff_result *const __restrict r) {
dr->level = 0; r->diff = 0;
dr->diff = 0; r->level = 0;
r->root_nkeys = 0;
if (unlikely(first->mc_signature != MDBX_MC_SIGNATURE || if (unlikely(y->mc_signature != MDBX_MC_SIGNATURE ||
last->mc_signature != MDBX_MC_SIGNATURE)) x->mc_signature != MDBX_MC_SIGNATURE))
return MDBX_EBADSIGN; return MDBX_EBADSIGN;
if (unlikely(first->mc_dbi != last->mc_dbi)) if (unlikely(y->mc_dbi != x->mc_dbi))
return MDBX_EINVAL; return MDBX_EINVAL;
if (unlikely(!(first->mc_flags & last->mc_flags & C_INITIALIZED))) if (unlikely(!(y->mc_flags & x->mc_flags & C_INITIALIZED)))
return MDBX_ENODATA; return MDBX_ENODATA;
while (likely(dr->level < first->mc_snum && dr->level < last->mc_snum)) { while (likely(r->level < y->mc_snum && r->level < x->mc_snum)) {
if (unlikely(first->mc_pg[dr->level] != last->mc_pg[dr->level])) if (unlikely(y->mc_pg[r->level] != x->mc_pg[r->level]))
return MDBX_PROBLEM; return MDBX_PROBLEM;
int nkeys = NUMKEYS(first->mc_pg[dr->level]); int nkeys = NUMKEYS(y->mc_pg[r->level]);
assert(nkeys > 0); assert(nkeys > 0);
if (dr->level == 0) if (r->level == 0)
dr->root_nkeys = nkeys; r->root_nkeys = nkeys;
int max_ki = nkeys - 1; const int limit_ki = nkeys - 1;
int last_ki = last->mc_ki[dr->level]; const int x_ki = x->mc_ki[r->level];
int first_ki = first->mc_ki[dr->level]; const int y_ki = y->mc_ki[r->level];
dr->diff = ((last_ki < max_ki) ? last_ki : max_ki) - r->diff = ((x_ki < limit_ki) ? x_ki : limit_ki) -
((first_ki < max_ki) ? first_ki : max_ki); ((y_ki < limit_ki) ? y_ki : limit_ki);
if (dr->diff == 0) { if (r->diff == 0) {
dr->level += 1; r->level += 1;
continue; continue;
} }
while (unlikely(dr->diff == 1) && likely(dr->level + 1 < first->mc_snum && while (unlikely(r->diff == 1) &&
dr->level + 1 < last->mc_snum)) { likely(r->level + 1 < y->mc_snum && r->level + 1 < x->mc_snum)) {
dr->level += 1; r->level += 1;
/* DB'PAGEs: 0------------------>MAX /* DB'PAGEs: 0------------------>MAX
* *
* CURSORs: first < last * CURSORs: y < x
* STACK[i ]: | * STACK[i ]: |
* STACK[+1]: ...f++N|0++l... * STACK[+1]: ...y++N|0++x...
*/ */
nkeys = NUMKEYS(first->mc_pg[dr->level]); nkeys = NUMKEYS(y->mc_pg[r->level]);
dr->diff = (nkeys - first->mc_ki[dr->level]) + last->mc_ki[dr->level]; r->diff = (nkeys - y->mc_ki[r->level]) + x->mc_ki[r->level];
assert(dr->diff > 0); assert(r->diff > 0);
} }
while (unlikely(dr->diff == -1) && likely(dr->level + 1 < first->mc_snum && while (unlikely(r->diff == -1) &&
dr->level + 1 < last->mc_snum)) { likely(r->level + 1 < y->mc_snum && r->level + 1 < x->mc_snum)) {
dr->level += 1; r->level += 1;
/* DB'PAGEs: 0------------------>MAX /* DB'PAGEs: 0------------------>MAX
* *
* CURSORs: last < first * CURSORs: x < y
* STACK[i ]: | * STACK[i ]: |
* STACK[+1]: ...l--N|0--f... * STACK[+1]: ...x--N|0--y...
*/ */
nkeys = NUMKEYS(last->mc_pg[dr->level]); nkeys = NUMKEYS(x->mc_pg[r->level]);
dr->diff = -(nkeys - last->mc_ki[dr->level]) - first->mc_ki[dr->level]; r->diff = -(nkeys - x->mc_ki[r->level]) - y->mc_ki[r->level];
assert(dr->diff < 0); assert(r->diff < 0);
} }
return MDBX_SUCCESS; return MDBX_SUCCESS;
} }
dr->diff = mdbx_cmp2int(last->mc_flags & C_EOF, first->mc_flags & C_EOF); r->diff = mdbx_cmp2int(x->mc_flags & C_EOF, y->mc_flags & C_EOF);
return MDBX_SUCCESS; return MDBX_SUCCESS;
} }
static ptrdiff_t estimate(const MDBX_db *db, __hot static ptrdiff_t estimate(const MDBX_db *db,
struct diff_result *const __restrict dr) { struct diff_result *const __restrict dr) {
/* root: branch-page => scale = leaf-factor * branch-factor(N-1) /* root: branch-page => scale = leaf-factor * branch-factor(N-1)
* level-1: branch-page(s) => scale = leaf-factor * branch-factor^2 * level-1: branch-page(s) => scale = leaf-factor * branch-factor^2
@ -13273,9 +13274,9 @@ static ptrdiff_t estimate(const MDBX_db *db,
return (ptrdiff_t)db->md_entries * dr->diff / (ptrdiff_t)dr->root_nkeys; return (ptrdiff_t)db->md_entries * dr->diff / (ptrdiff_t)dr->root_nkeys;
} }
/* average_branch_fillfactor = total(branch_entries) / branch_pages /* average_branchpage_fillfactor = total(branch_entries) / branch_pages
* total(branch_entries) = leaf_pages + branch_pages - 1 (root page) */ total(branch_entries) = leaf_pages + branch_pages - 1 (root page) */
const size_t log2_fixedpoint = 3; const size_t log2_fixedpoint = sizeof(size_t) - 1;
const size_t half = UINT64_C(1) << (log2_fixedpoint - 1); const size_t half = UINT64_C(1) << (log2_fixedpoint - 1);
const size_t factor = const size_t factor =
((db->md_leaf_pages + db->md_branch_pages - 1) << log2_fixedpoint) / ((db->md_leaf_pages + db->md_branch_pages - 1) << log2_fixedpoint) /
@ -13314,14 +13315,15 @@ static ptrdiff_t estimate(const MDBX_db *db,
} }
} }
int mdbx_estimate_distance(const MDBX_cursor *first, const MDBX_cursor *last, __hot int mdbx_estimate_distance(const MDBX_cursor *first,
const MDBX_cursor *last,
ptrdiff_t *distance_items) { ptrdiff_t *distance_items) {
if (unlikely(first == NULL || last == NULL || distance_items == NULL)) if (unlikely(first == NULL || last == NULL || distance_items == NULL))
return MDBX_EINVAL; return MDBX_EINVAL;
*distance_items = 0; *distance_items = 0;
struct diff_result dr; struct diff_result dr;
int rc = cursor_diff(first, last, &dr); int rc = cursor_diff(last, first, &dr);
if (unlikely(rc != MDBX_SUCCESS)) if (unlikely(rc != MDBX_SUCCESS))
return rc; return rc;