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tablets: load_balancer: Determine resize decision from target tablet count

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The flow is simpler this way, since the decision cannot now be
mismatched with target tablet count.
This commit is contained in:
Tomasz Grabiec
2025-02-11 21:51:16 +01:00
parent 35192e2d6f
commit e4c5e2ab55
1 changed files with 8 additions and 10 deletions
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18
service/tablet_allocator.cc
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@@ -1074,7 +1074,6 @@ public:
table_sizing& table_plan = plan.tables[table];
table_plan.current_tablet_count = tablet_count;
locator::resize_decision_way decision;
auto target_tablet_count = tablet_count;
auto min_tablet_count = std::max<size_t>(1,
@@ -1092,7 +1091,6 @@ public:
(cur_decision.is_split() && avg_tablet_size >= _target_tablet_size)) {
// TODO: extend to n-way split when needed
target_tablet_count *= 2;
decision = resize_decision::split{};
} else if (target_tablet_count / 2 >= min_tablet_count) {
// Consider merge, as long as it wouldn't violate min_tablet_count.
// If the current resize_decision is merge, apply hysteresis,
@@ -1100,7 +1098,6 @@ public:
if (avg_tablet_size < target_min_tablet_size() ||
(cur_decision.is_merge() && avg_tablet_size <= _target_tablet_size)) {
target_tablet_count /= 2;
decision = resize_decision::merge{};
}
}
@@ -1110,16 +1107,17 @@ public:
// Increasing will always bring us closer to the true target count, since tablet_count_from_size
// can only increase the count above it, but decreasing may go against the true target count
// if tablet_count_from_size would demand more tablets.
if (tablet_count < min_tablet_count) {
// TODO: extend to n-way split when needed
target_tablet_count = min_tablet_count;
decision = resize_decision::split{};
}
target_tablet_count = std::max(target_tablet_count, min_tablet_count);
}
table_plan.target_tablet_count = target_tablet_count;
table_plan.target_tablet_count_aligned = 1u << log2ceil(target_tablet_count);
table_plan.resize_decision = decision;
table_plan.target_tablet_count_aligned = 1u << log2ceil(table_plan.target_tablet_count);
if (table_plan.target_tablet_count_aligned > table_plan.current_tablet_count) {
table_plan.resize_decision = locator::resize_decision::split();
} else if (table_plan.target_tablet_count_aligned < table_plan.current_tablet_count) {
table_plan.resize_decision = locator::resize_decision::merge();
}
lblogger.debug("make_sizing_plan: table={}.{}, id={}, tablet_count={}, avg_tablet_size={}, min_tablet_count={}, target_tablet_count={}: decision={}",
s->ks_name(), s->cf_name(), s->id(), tablet_count, table_plan.avg_tablet_size, min_tablet_count, target_tablet_count, table_plan.resize_decision);