TLA Line data Source code
1 : use anyhow::Context;
2 : use once_cell::sync::OnceCell;
3 :
4 : use tokio::sync::Semaphore;
5 : use utils::lsn::Lsn;
6 :
7 : use std::sync::atomic::{AtomicI64, Ordering as AtomicOrdering};
8 : use std::sync::Arc;
9 :
10 : /// Internal structure to hold all data needed for logical size calculation.
11 : ///
12 : /// Calculation consists of two stages:
13 : ///
14 : /// 1. Initial size calculation. That might take a long time, because it requires
15 : /// reading all layers containing relation sizes at `initial_part_end`.
16 : ///
17 : /// 2. Collecting an incremental part and adding that to the initial size.
18 : /// Increments are appended on walreceiver writing new timeline data,
19 : /// which result in increase or decrease of the logical size.
20 : pub(super) struct LogicalSize {
21 : /// Size, potentially slow to compute. Calculating this might require reading multiple
22 : /// layers, and even ancestor's layers.
23 : ///
24 : /// NOTE: size at a given LSN is constant, but after a restart we will calculate
25 : /// the initial size at a different LSN.
26 : pub initial_logical_size: OnceCell<u64>,
27 :
28 : /// Semaphore to track ongoing calculation of `initial_logical_size`.
29 : pub initial_size_computation: Arc<tokio::sync::Semaphore>,
30 :
31 : /// Latest Lsn that has its size uncalculated, could be absent for freshly created timelines.
32 : pub initial_part_end: Option<Lsn>,
33 :
34 : /// All other size changes after startup, combined together.
35 : ///
36 : /// Size shouldn't ever be negative, but this is signed for two reasons:
37 : ///
38 : /// 1. If we initialized the "baseline" size lazily, while we already
39 : /// process incoming WAL, the incoming WAL records could decrement the
40 : /// variable and temporarily make it negative. (This is just future-proofing;
41 : /// the initialization is currently not done lazily.)
42 : ///
43 : /// 2. If there is a bug and we e.g. forget to increment it in some cases
44 : /// when size grows, but remember to decrement it when it shrinks again, the
45 : /// variable could go negative. In that case, it seems better to at least
46 : /// try to keep tracking it, rather than clamp or overflow it. Note that
47 : /// get_current_logical_size() will clamp the returned value to zero if it's
48 : /// negative, and log an error. Could set it permanently to zero or some
49 : /// special value to indicate "broken" instead, but this will do for now.
50 : ///
51 : /// Note that we also expose a copy of this value as a prometheus metric,
52 : /// see `current_logical_size_gauge`. Use the `update_current_logical_size`
53 : /// to modify this, it will also keep the prometheus metric in sync.
54 : pub size_added_after_initial: AtomicI64,
55 : }
56 :
57 : /// Normalized current size, that the data in pageserver occupies.
58 UBC 0 : #[derive(Debug, Clone, Copy)]
59 : pub(super) enum CurrentLogicalSize {
60 : /// The size is not yet calculated to the end, this is an intermediate result,
61 : /// constructed from walreceiver increments and normalized: logical data could delete some objects, hence be negative,
62 : /// yet total logical size cannot be below 0.
63 : Approximate(u64),
64 : // Fully calculated logical size, only other future walreceiver increments are changing it, and those changes are
65 : // available for observation without any calculations.
66 : Exact(u64),
67 : }
68 :
69 : impl CurrentLogicalSize {
70 CBC 779585 : pub(super) fn size(&self) -> u64 {
71 779585 : *match self {
72 717 : Self::Approximate(size) => size,
73 778868 : Self::Exact(size) => size,
74 : }
75 779585 : }
76 : }
77 :
78 : impl LogicalSize {
79 617 : pub(super) fn empty_initial() -> Self {
80 617 : Self {
81 617 : initial_logical_size: OnceCell::with_value(0),
82 617 : // initial_logical_size already computed, so, don't admit any calculations
83 617 : initial_size_computation: Arc::new(Semaphore::new(0)),
84 617 : initial_part_end: None,
85 617 : size_added_after_initial: AtomicI64::new(0),
86 617 : }
87 617 : }
88 :
89 685 : pub(super) fn deferred_initial(compute_to: Lsn) -> Self {
90 685 : Self {
91 685 : initial_logical_size: OnceCell::new(),
92 685 : initial_size_computation: Arc::new(Semaphore::new(1)),
93 685 : initial_part_end: Some(compute_to),
94 685 : size_added_after_initial: AtomicI64::new(0),
95 685 : }
96 685 : }
97 :
98 1808627 : pub(super) fn current_size(&self) -> anyhow::Result<CurrentLogicalSize> {
99 1808627 : let size_increment: i64 = self.size_added_after_initial.load(AtomicOrdering::Acquire);
100 1808627 : // ^^^ keep this type explicit so that the casts in this function break if
101 1808627 : // we change the type.
102 1808627 : match self.initial_logical_size.get() {
103 1806418 : Some(initial_size) => {
104 1806418 : initial_size.checked_add_signed(size_increment)
105 1806418 : .with_context(|| format!("Overflow during logical size calculation, initial_size: {initial_size}, size_increment: {size_increment}"))
106 1806418 : .map(CurrentLogicalSize::Exact)
107 : }
108 : None => {
109 2209 : let non_negative_size_increment = u64::try_from(size_increment).unwrap_or(0);
110 2209 : Ok(CurrentLogicalSize::Approximate(non_negative_size_increment))
111 : }
112 : }
113 1808627 : }
114 :
115 1029042 : pub(super) fn increment_size(&self, delta: i64) {
116 1029042 : self.size_added_after_initial
117 1029042 : .fetch_add(delta, AtomicOrdering::SeqCst);
118 1029042 : }
119 :
120 : /// Make the value computed by initial logical size computation
121 : /// available for re-use. This doesn't contain the incremental part.
122 : pub(super) fn initialized_size(&self, lsn: Lsn) -> Option<u64> {
123 400 : match self.initial_part_end {
124 400 : Some(v) if v == lsn => self.initial_logical_size.get().copied(),
125 40 : _ => None,
126 : }
127 416 : }
128 : }
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