Line data Source code
1 : use crate::{SegmentMethod, SegmentSizeResult, SizeResult, StorageModel};
2 :
3 : //
4 : // *-g--*---D--->
5 : // /
6 : // /
7 : // / *---b----*-B--->
8 : // / /
9 : // / /
10 : // -----*--e---*-----f----* C
11 : // E \
12 : // \
13 : // *--a---*---A-->
14 : //
15 : // If A and B need to be retained, is it cheaper to store
16 : // snapshot at C+a+b, or snapshots at A and B ?
17 : //
18 : // If D also needs to be retained, which is cheaper:
19 : //
20 : // 1. E+g+e+f+a+b
21 : // 2. D+C+a+b
22 : // 3. D+A+B
23 :
24 : /// `Segment` which has had its size calculated.
25 : #[derive(Clone, Debug)]
26 : struct SegmentSize {
27 : method: SegmentMethod,
28 :
29 : // calculated size of this subtree, using this method
30 : accum_size: u64,
31 :
32 : seg_id: usize,
33 : children: Vec<SegmentSize>,
34 : }
35 :
36 : struct SizeAlternatives {
37 : /// cheapest alternative if parent is available.
38 : incremental: SegmentSize,
39 :
40 : /// cheapest alternative if parent node is not available
41 : non_incremental: Option<SegmentSize>,
42 : }
43 :
44 : impl StorageModel {
45 8 : pub fn calculate(&self) -> SizeResult {
46 : // Build adjacency list. 'child_list' is indexed by segment id. Each entry
47 : // contains a list of all child segments of the segment.
48 8 : let mut roots: Vec<usize> = Vec::new();
49 8 : let mut child_list: Vec<Vec<usize>> = Vec::new();
50 8 : child_list.resize(self.segments.len(), Vec::new());
51 :
52 71 : for (seg_id, seg) in self.segments.iter().enumerate() {
53 71 : if let Some(parent_id) = seg.parent {
54 63 : child_list[parent_id].push(seg_id);
55 63 : } else {
56 8 : roots.push(seg_id);
57 8 : }
58 : }
59 :
60 8 : let mut segment_results = Vec::new();
61 8 : segment_results.resize(
62 8 : self.segments.len(),
63 8 : SegmentSizeResult {
64 8 : method: SegmentMethod::Skipped,
65 8 : accum_size: 0,
66 8 : },
67 : );
68 :
69 8 : let mut total_size = 0;
70 16 : for root in roots {
71 8 : if let Some(selected) = self.size_here(root, &child_list).non_incremental {
72 8 : StorageModel::fill_selected_sizes(&selected, &mut segment_results);
73 8 : total_size += selected.accum_size;
74 8 : } else {
75 0 : // Couldn't find any way to get this root. Error?
76 0 : }
77 : }
78 :
79 8 : SizeResult {
80 8 : // If total_size is 0, it means that the tenant has all timelines offloaded; we need to report 1
81 8 : // here so that the data point shows up in the s3 files.
82 8 : total_size: total_size.max(1),
83 8 : segments: segment_results,
84 8 : }
85 8 : }
86 :
87 71 : fn fill_selected_sizes(selected: &SegmentSize, result: &mut Vec<SegmentSizeResult>) {
88 71 : result[selected.seg_id] = SegmentSizeResult {
89 71 : method: selected.method,
90 71 : accum_size: selected.accum_size,
91 71 : };
92 : // recurse to children
93 71 : for child in selected.children.iter() {
94 63 : StorageModel::fill_selected_sizes(child, result);
95 63 : }
96 71 : }
97 :
98 : //
99 : // This is the core of the sizing calculation.
100 : //
101 : // This is a recursive function, that for each Segment calculates the best way
102 : // to reach all the Segments that are marked as needed in this subtree, under two
103 : // different conditions:
104 : // a) when the parent of this segment is available (as a snaphot or through WAL), and
105 : // b) when the parent of this segment is not available.
106 : //
107 71 : fn size_here(&self, seg_id: usize, child_list: &Vec<Vec<usize>>) -> SizeAlternatives {
108 71 : let seg = &self.segments[seg_id];
109 : // First figure out the best way to get each child
110 71 : let mut children = Vec::new();
111 71 : for child_id in &child_list[seg_id] {
112 63 : children.push(self.size_here(*child_id, child_list))
113 : }
114 :
115 : // Method 1. If this node is not needed, we can skip it as long as we
116 : // take snapshots later in each sub-tree
117 71 : let snapshot_later = if !seg.needed {
118 53 : let mut snapshot_later = SegmentSize {
119 53 : seg_id,
120 53 : method: SegmentMethod::Skipped,
121 53 : accum_size: 0,
122 53 : children: Vec::new(),
123 53 : };
124 :
125 53 : let mut possible = true;
126 54 : for child in children.iter() {
127 54 : if let Some(non_incremental) = &child.non_incremental {
128 40 : snapshot_later.accum_size += non_incremental.accum_size;
129 40 : snapshot_later.children.push(non_incremental.clone())
130 : } else {
131 14 : possible = false;
132 14 : break;
133 : }
134 : }
135 53 : if possible { Some(snapshot_later) } else { None }
136 : } else {
137 18 : None
138 : };
139 :
140 : // Method 2. Get a snapshot here. This assumed to be possible, if the 'size' of
141 : // this Segment was given.
142 71 : let snapshot_here = if !seg.needed || seg.parent.is_none() {
143 53 : if let Some(snapshot_size) = seg.size {
144 49 : let mut snapshot_here = SegmentSize {
145 49 : seg_id,
146 49 : method: SegmentMethod::SnapshotHere,
147 49 : accum_size: snapshot_size,
148 49 : children: Vec::new(),
149 49 : };
150 57 : for child in children.iter() {
151 57 : snapshot_here.accum_size += child.incremental.accum_size;
152 57 : snapshot_here.children.push(child.incremental.clone())
153 : }
154 49 : Some(snapshot_here)
155 : } else {
156 4 : None
157 : }
158 : } else {
159 18 : None
160 : };
161 :
162 : // Method 3. Use WAL to get here from parent
163 71 : let wal_here = {
164 71 : let mut wal_here = SegmentSize {
165 71 : seg_id,
166 71 : method: SegmentMethod::Wal,
167 71 : accum_size: if let Some(parent_id) = seg.parent {
168 63 : seg.lsn - self.segments[parent_id].lsn
169 : } else {
170 8 : 0
171 : },
172 71 : children: Vec::new(),
173 : };
174 134 : for child in children {
175 63 : wal_here.accum_size += child.incremental.accum_size;
176 63 : wal_here.children.push(child.incremental)
177 : }
178 71 : wal_here
179 : };
180 :
181 : // If the parent is not available, what's the cheapest method involving
182 : // a snapshot here or later?
183 71 : let mut cheapest_non_incremental: Option<SegmentSize> = None;
184 71 : if let Some(snapshot_here) = snapshot_here {
185 49 : cheapest_non_incremental = Some(snapshot_here);
186 49 : }
187 71 : if let Some(snapshot_later) = snapshot_later {
188 : // Use <=, to prefer skipping if the size is equal
189 39 : if let Some(parent) = &cheapest_non_incremental {
190 35 : if snapshot_later.accum_size <= parent.accum_size {
191 34 : cheapest_non_incremental = Some(snapshot_later);
192 34 : }
193 4 : } else {
194 4 : cheapest_non_incremental = Some(snapshot_later);
195 4 : }
196 32 : }
197 :
198 : // And what's the cheapest method, if the parent is available?
199 71 : let cheapest_incremental = if let Some(cheapest_non_incremental) = &cheapest_non_incremental
200 : {
201 : // Is it cheaper to use a snapshot here or later, anyway?
202 : // Use <, to prefer Wal over snapshot if the cost is the same
203 53 : if wal_here.accum_size < cheapest_non_incremental.accum_size {
204 32 : wal_here
205 : } else {
206 21 : cheapest_non_incremental.clone()
207 : }
208 : } else {
209 18 : wal_here
210 : };
211 :
212 71 : SizeAlternatives {
213 71 : incremental: cheapest_incremental,
214 71 : non_incremental: cheapest_non_incremental,
215 71 : }
216 71 : }
217 : }
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