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annotate rust/hg-core/src/revlog/nodemap_docket.rs @ 46091:9eb07ab3f2d4

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rhg: use persistent nodemap when available ? for node ID ? revision number lookups, instead on linear scan in a revlog. Differential Revision: https://phab.mercurial-scm.org/D9520
author Simon Sapin <simon-commits@exyr.org>
date Fri, 04 Dec 2020 17:27:10 +0100
parents
children 8a4914397d02
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46091
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1 use memmap::Mmap;
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2 use std::convert::TryInto;
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3 use std::path::{Path, PathBuf};
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4
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5 use super::revlog::{mmap_open, RevlogError};
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6 use crate::utils::strip_suffix;
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7
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8 const ONDISK_VERSION: u8 = 1;
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9
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10 pub(super) struct NodeMapDocket {
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11 pub data_length: usize,
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12 // TODO: keep here more of the data from `parse()` when we need it
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13 }
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14
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15 impl NodeMapDocket {
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16 /// Return `Ok(None)` when the caller should proceed without a persistent
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17 /// nodemap:
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18 ///
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19 /// * This revlog does not have a `.n` docket file (it is not generated for
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20 /// small revlogs), or
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21 /// * The docket has an unsupported version number (repositories created by
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22 /// later hg, maybe that should be a requirement instead?), or
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23 /// * The docket file points to a missing (likely deleted) data file (this
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24 /// can happen in a rare race condition).
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25 pub fn read_from_file(
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26 index_path: &Path,
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27 ) -> Result<Option<(Self, Mmap)>, RevlogError> {
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28 let docket_path = index_path.with_extension("n");
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29 let docket_bytes = match std::fs::read(&docket_path) {
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30 Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
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31 return Ok(None)
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32 }
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33 Err(e) => return Err(RevlogError::IoError(e)),
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34 Ok(bytes) => bytes,
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35 };
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36
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37 let mut input = if let Some((&ONDISK_VERSION, rest)) =
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38 docket_bytes.split_first()
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39 {
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40 rest
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41 } else {
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42 return Ok(None);
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43 };
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44 let input = &mut input;
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45
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46 let uid_size = read_u8(input)? as usize;
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47 let _tip_rev = read_be_u64(input)?;
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48 // TODO: do we care about overflow for 4 GB+ nodemap files on 32-bit
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49 // systems?
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50 let data_length = read_be_u64(input)? as usize;
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51 let _data_unused = read_be_u64(input)?;
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52 let tip_node_size = read_be_u64(input)? as usize;
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53 let uid = read_bytes(input, uid_size)?;
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54 let _tip_node = read_bytes(input, tip_node_size)?;
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55
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56 let uid =
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57 std::str::from_utf8(uid).map_err(|_| RevlogError::Corrupted)?;
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58 let docket = NodeMapDocket { data_length };
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59
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60 let data_path = rawdata_path(&docket_path, uid);
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61 // TODO: use `std::fs::read` here when the `persistent-nodemap.mmap`
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62 // config is false?
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63 match mmap_open(&data_path) {
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64 Ok(mmap) => {
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65 if mmap.len() >= data_length {
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66 Ok(Some((docket, mmap)))
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67 } else {
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68 Err(RevlogError::Corrupted)
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69 }
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70 }
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71 Err(error) => {
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72 if error.kind() == std::io::ErrorKind::NotFound {
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73 Ok(None)
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74 } else {
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75 Err(RevlogError::IoError(error))
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76 }
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77 }
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78 }
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79 }
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80 }
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81
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82 fn read_bytes<'a>(
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83 input: &mut &'a [u8],
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84 count: usize,
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85 ) -> Result<&'a [u8], RevlogError> {
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86 if let Some(start) = input.get(..count) {
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87 *input = &input[count..];
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88 Ok(start)
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89 } else {
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90 Err(RevlogError::Corrupted)
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91 }
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92 }
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93
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94 fn read_u8<'a>(input: &mut &[u8]) -> Result<u8, RevlogError> {
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95 Ok(read_bytes(input, 1)?[0])
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96 }
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97
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98 fn read_be_u64<'a>(input: &mut &[u8]) -> Result<u64, RevlogError> {
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99 let array = read_bytes(input, std::mem::size_of::<u64>())?
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100 .try_into()
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101 .unwrap();
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102 Ok(u64::from_be_bytes(array))
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103 }
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104
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105 fn rawdata_path(docket_path: &Path, uid: &str) -> PathBuf {
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106 let docket_name = docket_path
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107 .file_name()
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108 .expect("expected a base name")
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109 .to_str()
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110 .expect("expected an ASCII file name in the store");
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111 let prefix = strip_suffix(docket_name, ".n.a")
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112 .or_else(|| strip_suffix(docket_name, ".n"))
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113 .expect("expected docket path in .n or .n.a");
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114 let name = format!("{}-{}.nd", prefix, uid);
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115 docket_path
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116 .parent()
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117 .expect("expected a non-root path")
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118 .join(name)
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119 }