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mvcc: partition_snapshot_row_cursor: Handle non-evictable snapshots

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This is a prerequisite for using the cursor in memtable readers.

Non-evictable snapshots are those which live in memtables. Unlike
evictable snapshots, they don't have a dummy entry at position after
all clustering rows. In evictable snapshots, lookup always finds an
entry, not so with non-evictable snapshots. The cursor was not
prepared for this case, this patch handles it.
This commit is contained in:
Tomasz Grabiec
2022-11-21 18:23:18 +01:00
parent 091ad8f6ee
commit 6b7473be53
1 changed files with 31 additions and 12 deletions
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43
partition_snapshot_row_cursor.hh
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@@ -250,6 +250,19 @@ class partition_snapshot_row_cursor final {
if (pos) [[likely]] {
_heap.emplace_back(position_in_version{pos, std::move(rows), version_no, unique_owner, cont});
}
} else {
if (_reversed) [[unlikely]] {
if (!rows.empty()) {
pos = std::prev(rows.end());
} else {
_background_continuity = true;
}
} else {
_background_continuity = true; // Default continuity past the last entry
}
if (pos) [[likely]] {
_heap.emplace_back(position_in_version{pos, std::move(rows), version_no, unique_owner, is_continuous::yes});
}
}
++version_no;
first = false;
@@ -380,22 +393,28 @@ public:
_latest_it = it;
auto heap_i = boost::find_if(_heap, [](auto&& v) { return v.version_no == 0; });
is_continuous cont = it->continuous();
if (_reversed) [[unlikely]] {
if (!match) {
// lower_bound() in reverse order points to predecessor of it unless the keys are equal.
if (it == rows.begin()) {
_background_continuity |= bool(it->continuous());
it = {};
is_continuous cont;
if (it) {
if (_reversed) [[unlikely]] {
if (!match) {
// lower_bound() in reverse order points to predecessor of it unless the keys are equal.
if (it == rows.begin()) {
_background_continuity |= bool(it->continuous());
it = {};
} else {
cont = it->continuous();
--it;
}
} else {
cont = it->continuous();
--it;
// We can put anything in the match case since this continuity will not be used
// when advancing the cursor.
cont = is_continuous::no;
}
} else {
// We can put anything in the match case since this continuity will not be used
// when advancing the cursor.
cont = is_continuous::no;
cont = it->continuous();
}
} else {
_background_continuity = true; // Default continuity past the last entry.
}
if (!it) {