[pbs-devel] [RFC pxar proxmox-backup 00/36] fix #3174: improve file-level backup

[Christian Ebner <c.ebner@proxmox.com>]

Disclaimer: This patches are work in progress and not intended for
production use just yet. The purpose is for initial testing and review.

This series of patches implements an metadata based file change
detection mechanism for improved pxar file level backup creation speed
for unchanged files.

The chosen approach is to split pxar archives on creation via the
proxmox-backup-client into two separate archives and upload streams,
one exclusive for regular file payloads, the other one for the rest
of the pxar archive, which is mostly metadata.

On consecutive runs, the metadata archive of the previous backup run,
which is limited in size and therefore rapidly accessed is used to
lookup and compare the metadata for entries to encode.
This assumes that the connection speed to the Proxmox Backup Server is
sufficiently fast, allowing the download and chaching of the chunks for
that index.

Changes to regular files are detected by comparing all of the files
metadata object, including mtime, acls, ecc. If no changes are detected,
the previous payload index is used to lookup chunks to possibly re-use
in the payload stream of the new archive.
In order to reduce possible chunk fragmentation, the decision whether to
re-use or re-encode a file payload is deferred until enough information
is gathered by adding entries to a look-ahead cache. If enough payload
is referenced, the chunks are re-used and injected into the pxar payload
upload stream, otherwise they are discated and the files encoded
regularly.

The following lists the most notable changes included in this series since
the version 1:
- also cache pxar exclude pattern passed via cli instead of encoding
  them directly. This lead to an inconsistent archive while caching.
- Fix the flushing of entries and chunks to inject before finishing the
  archiver. Previously these last entries have been re-encoded, now they
  are re-used.
- add a dedicated method and type in the decoder for decoding payload
  references.

An invocation of a backup run with this patches now is:
```bash
proxmox-backup-client backup <label>.pxar:<source-path> --change-detection-mode=metadata
```
During the first run, no reference index is available, the pxar archive
will however be split into the two parts.
Following backups will however utilize the pxar archive accessor and
index files of the previous run to perform file change detection.

As benchmarks, the linux source code as well as the coco dataset for
computer vision and pattern recognition can be used.
The benchmarks can be performed by running:
```bash
proxmox-backup-test-suite detection-mode-bench prepare --target /<path-to-bench-source-target>
proxmox-backup-test-suite detection-mode-bench run linux.pxar:/<path-to-bench-source-target>/linux
proxmox-backup-test-suite detection-mode-bench run coco.pxar:/<path-to-bench-source-target>/coco
```

Above command invocations assume the default repository and credentials
to be set as environment variables, they might however be passed as
additional optional parameters instead.

Benchmark runs using these test data show a significant improvement in
the time needed for the backups. Note that all of these results were to a local
PBS instance within a VM, minimizing therefore possible influences by the network.

For the linux source code backup:
    Completed benchmark with 5 runs for each tested mode.

    Completed regular backup with:
    Total runtime: 51.31 s
    Average: 10.26 ± 0.12 s
    Min: 10.16 s
    Max: 10.46 s

    Completed metadata detection mode backup with:
    Total runtime: 4.89 s
    Average: 0.98 ± 0.02 s
    Min: 0.95 s
    Max: 1.00 s

    Differences (metadata based - regular):
    Delta total runtime: -46.42 s (-90.47 %)
    Delta average: -9.28 ± 0.12 s (-90.47 %)
    Delta min: -9.21 s (-90.64 %)
    Delta max: -9.46 s (-90.44 %)

For the coco dataset backup:
    Completed benchmark with 5 runs for each tested mode.

    Completed regular backup with:
    Total runtime: 520.72 s
    Average: 104.14 ± 0.79 s
    Min: 103.44 s
    Max: 105.49 s

    Completed metadata detection mode backup with:
    Total runtime: 6.95 s
    Average: 1.39 ± 0.23 s
    Min: 1.26 s
    Max: 1.79 s

    Differences (metadata based - regular):
    Delta total runtime: -513.76 s (-98.66 %)
    Delta average: -102.75 ± 0.83 s (-98.66 %)
    Delta min: -102.18 s (-98.78 %)
    Delta max: -103.69 s (-98.30 %)

This series of patches implements an alternative, but more promising
approach to the series presented previously [0], with the intention to
solve the same issue with less changes required to the pxar format and to
be more efficient.

[0] https://lists.proxmox.com/pipermail/pbs-devel/2024-January/007693.html

pxar:

Christian Ebner (10):
  format/examples: add PXAR_PAYLOAD_REF entry header
  encoder: add optional output writer for file payloads
  format/decoder: add method to read payload references
  decoder: add optional payload input stream
  accessor: add optional payload input stream
  encoder: move to stack based state tracking
  encoder: add payload reference capability
  encoder: add payload position capability
  encoder: add payload advance capability
  encoder/format: finish payload stream with marker

 examples/mk-format-hashes.rs |  10 +
 examples/pxarcmd.rs          |   6 +-
 src/accessor/aio.rs          |   7 +
 src/accessor/mod.rs          |  85 ++++++++-
 src/decoder/mod.rs           |  92 ++++++++-
 src/decoder/sync.rs          |   7 +
 src/encoder/aio.rs           |  52 +++--
 src/encoder/mod.rs           | 357 +++++++++++++++++++++++++----------
 src/encoder/sync.rs          |  45 ++++-
 src/format/mod.rs            |  10 +
 src/lib.rs                   |   3 +
 11 files changed, 534 insertions(+), 140 deletions(-)

proxmox-backup:

Christian Ebner (26):
  client: pxar: switch to stack based encoder state
  client: backup: factor out extension from backup target
  client: backup: early check for fixed index type
  client: backup: split payload to dedicated stream
  client: restore: read payload from dedicated index
  tools: cover meta extension for pxar archives
  restore: cover meta extension for pxar archives
  client: mount: make split pxar archives mountable
  api: datastore: refactor getting local chunk reader
  api: datastore: attach optional payload chunk reader
  catalog: shell: factor out pxar fuse reader instantiation
  catalog: shell: redirect payload reader for split streams
  www: cover meta extension for pxar archives
  index: fetch chunk form index by start/end-offset
  upload stream: impl reused chunk injector
  client: chunk stream: add chunk injection queues
  client: implement prepare reference method
  client: pxar: implement store to insert chunks on caching
  client: pxar: add previous reference to archiver
  client: pxar: add method for metadata comparison
  specs: add backup detection mode specification
  pxar: caching: add look-ahead cache types
  client: pxar: add look-ahead caching
  fix #3174: client: pxar: enable caching and meta comparison
  test-suite: add detection mode change benchmark
  test-suite: Add bin to deb, add shell completions

 Cargo.toml                                    |   1 +
 Makefile                                      |  13 +-
 debian/proxmox-backup-client.bash-completion  |   1 +
 debian/proxmox-backup-client.install          |   2 +
 debian/proxmox-backup-test-suite.bc           |   8 +
 examples/test_chunk_speed2.rs                 |  10 +-
 pbs-client/src/backup_specification.rs        |  53 ++
 pbs-client/src/backup_writer.rs               |  89 ++-
 pbs-client/src/chunk_stream.rs                |  42 +-
 pbs-client/src/inject_reused_chunks.rs        | 152 +++++
 pbs-client/src/lib.rs                         |   1 +
 pbs-client/src/pxar/create.rs                 | 620 +++++++++++++++++-
 pbs-client/src/pxar/look_ahead_cache.rs       |  40 ++
 pbs-client/src/pxar/mod.rs                    |   3 +-
 pbs-client/src/pxar_backup_stream.rs          |  54 +-
 pbs-client/src/tools/mod.rs                   |   2 +-
 pbs-datastore/src/dynamic_index.rs            |  55 ++
 proxmox-backup-client/src/catalog.rs          |  73 ++-
 proxmox-backup-client/src/main.rs             | 280 +++++++-
 proxmox-backup-client/src/mount.rs            |  56 +-
 proxmox-backup-test-suite/Cargo.toml          |  18 +
 .../src/detection_mode_bench.rs               | 294 +++++++++
 proxmox-backup-test-suite/src/main.rs         |  17 +
 proxmox-file-restore/src/main.rs              |  11 +-
 .../src/proxmox_restore_daemon/api.rs         |  16 +-
 pxar-bin/src/main.rs                          |   7 +-
 src/api2/admin/datastore.rs                   |  45 +-
 tests/catar.rs                                |   4 +
 www/datastore/Content.js                      |   6 +-
 zsh-completions/_proxmox-backup-test-suite    |  13 +
 30 files changed, 1827 insertions(+), 159 deletions(-)
 create mode 100644 debian/proxmox-backup-test-suite.bc
 create mode 100644 pbs-client/src/inject_reused_chunks.rs
 create mode 100644 pbs-client/src/pxar/look_ahead_cache.rs
 create mode 100644 proxmox-backup-test-suite/Cargo.toml
 create mode 100644 proxmox-backup-test-suite/src/detection_mode_bench.rs
 create mode 100644 proxmox-backup-test-suite/src/main.rs
 create mode 100644 zsh-completions/_proxmox-backup-test-suite

-- 
2.39.2