Mercurial > public > mercurial-scm > hg
comparison mercurial/revlog.py @ 47246:02a4463565ea
revlog: improve documentation of the entry tuple
The code in revlog, and outside revlog directly use the index's entry tuple,
with direct integer indexing. This is a voluntary trade off to obtains better
performance from the Python code at the expense of the developers sanity.
Let's at least have a clear and central documentation about what this tuple is
about.
Differential Revision: https://phab.mercurial-scm.org/D10643
| author | Pierre-Yves David <pierre-yves.david@octobus.net> |
|---|---|
| date | Mon, 03 May 2021 16:52:38 +0200 |
| parents | de63be070e02 |
| children | 130c9f7ed914 |
comparison
equal
deleted
inserted
replaced
| 47245:de63be070e02 | 47246:02a4463565ea |
|---|---|
| 282 | 282 |
| 283 `concurrencychecker` is an optional function that receives 3 arguments: a | 283 `concurrencychecker` is an optional function that receives 3 arguments: a |
| 284 file handle, a filename, and an expected position. It should check whether | 284 file handle, a filename, and an expected position. It should check whether |
| 285 the current position in the file handle is valid, and log/warn/fail (by | 285 the current position in the file handle is valid, and log/warn/fail (by |
| 286 raising). | 286 raising). |
| 287 | |
| 288 | |
| 289 Internal details | |
| 290 ---------------- | |
| 291 | |
| 292 A large part of the revlog logic deals with revisions' "index entries", tuple | |
| 293 objects that contains the same "items" whatever the revlog version. | |
| 294 Different versions will have different ways of storing these items (sometimes | |
| 295 not having them at all), but the tuple will always be the same. New fields | |
| 296 are usually added at the end to avoid breaking existing code that relies | |
| 297 on the existing order. The field are defined as follows: | |
| 298 | |
| 299 [0] offset: | |
| 300 The byte index of the start of revision data chunk. | |
| 301 That value is shifted up by 16 bits. use "offset = field >> 16" to | |
| 302 retrieve it. | |
| 303 | |
| 304 flags: | |
| 305 A flag field that carries special information or changes the behavior | |
| 306 of the revision. (see `REVIDX_*` constants for details) | |
| 307 The flag field only occupies the first 16 bits of this field, | |
| 308 use "flags = field & 0xFFFF" to retrieve the value. | |
| 309 | |
| 310 [1] compressed length: | |
| 311 The size, in bytes, of the chunk on disk | |
| 312 | |
| 313 [2] uncompressed length: | |
| 314 The size, in bytes, of the full revision once reconstructed. | |
| 315 | |
| 316 [3] base rev: | |
| 317 Either the base of the revision delta chain (without general | |
| 318 delta), or the base of the delta (stored in the data chunk) | |
| 319 with general delta. | |
| 320 | |
| 321 [4] link rev: | |
| 322 Changelog revision number of the changeset introducing this | |
| 323 revision. | |
| 324 | |
| 325 [5] parent 1 rev: | |
| 326 Revision number of the first parent | |
| 327 | |
| 328 [6] parent 2 rev: | |
| 329 Revision number of the second parent | |
| 330 | |
| 331 [7] node id: | |
| 332 The node id of the current revision | |
| 333 | |
| 334 [8] sidedata offset: | |
| 335 The byte index of the start of the revision's side-data chunk. | |
| 336 | |
| 337 [9] sidedata chunk length: | |
| 338 The size, in bytes, of the revision's side-data chunk. | |
| 287 """ | 339 """ |
| 288 | 340 |
| 289 _flagserrorclass = error.RevlogError | 341 _flagserrorclass = error.RevlogError |
| 290 | 342 |
| 291 def __init__( | 343 def __init__( |