Hex Artifact Content
Not logged in

Artifact e5d3578c4bf05ec5f7b8255f411296efb1583389:

File www/selfcheck.wiki part of check-in [d87ca60c58] - initial ports of static .html to static /doc .wiki by stephan on 2008-05-15 20:25:46. Also file www/selfcheck.wiki part of check-in [f94f7e5f49] - Merge the fork back together. by drh on 2008-05-16 00:27:49.

0000: 3c 68 31 20 61 6c 69 67 6e 3d 22 63 65 6e 74 65  <h1 align="cente
0010: 72 22 3e 0a 46 6f 73 73 69 6c 20 52 65 70 6f 73  r">.Fossil Repos
0020: 69 74 6f 72 79 20 49 6e 74 65 67 72 69 74 79 20  itory Integrity 
0030: 53 65 6c 66 2d 43 68 65 63 6b 73 0a 3c 2f 68 31  Self-Checks.</h1
0040: 3e 0a 0a 3c 70 3e 0a 45 76 65 6e 20 74 68 6f 75  >..<p>.Even thou
0050: 67 68 20 66 6f 73 73 69 6c 20 69 73 20 61 20 72  gh fossil is a r
0060: 65 6c 61 74 69 76 65 6c 79 20 6e 65 77 20 70 72  elatively new pr
0070: 6f 6a 65 63 74 20 61 6e 64 20 73 74 69 6c 6c 20  oject and still 
0080: 63 6f 6e 74 61 69 6e 73 0a 6d 61 6e 79 20 62 75  contains.many bu
0090: 67 73 2c 20 69 74 20 69 73 20 64 65 73 69 67 6e  gs, it is design
00a0: 65 64 20 77 69 74 68 20 66 65 61 74 75 72 65 73  ed with features
00b0: 20 74 6f 20 67 69 76 65 20 69 74 20 61 20 68 69   to give it a hi
00c0: 67 68 20 6c 65 76 65 6c 0a 6f 66 20 69 6e 74 65  gh level.of inte
00d0: 67 72 69 74 79 20 73 6f 20 74 68 61 74 20 79 6f  grity so that yo
00e0: 75 20 63 61 6e 20 68 61 76 65 20 63 6f 6e 66 69  u can have confi
00f0: 64 65 6e 63 65 20 74 68 61 74 20 79 6f 75 20 77  dence that you w
0100: 69 6c 6c 20 6e 6f 74 0a 6c 6f 73 65 20 79 6f 75  ill not.lose you
0110: 72 20 66 69 6c 65 73 2e 20 20 54 68 69 73 20 6e  r files.  This n
0120: 6f 74 65 20 64 65 73 63 72 69 62 65 73 20 74 68  ote describes th
0130: 65 20 64 65 66 65 6e 73 69 76 65 20 6d 65 61 73  e defensive meas
0140: 75 72 65 73 20 74 68 61 74 0a 66 6f 73 73 69 6c  ures that.fossil
0150: 20 75 73 65 73 20 74 6f 20 68 65 6c 70 20 70 72   uses to help pr
0160: 65 76 65 6e 74 20 66 69 6c 65 20 6c 6f 73 73 20  event file loss 
0170: 64 75 65 20 74 6f 20 62 75 67 73 2e 0a 3c 2f 70  due to bugs..</p
0180: 3e 0a 0a 3c 70 3e 3c 69 3e 46 6f 6c 6c 6f 77 2d  >..<p><i>Follow-
0190: 75 70 20 61 73 20 6f 66 20 32 30 30 37 2d 31 31  up as of 2007-11
01a0: 2d 32 34 3a 3c 2f 69 3e 0a 46 6f 73 73 69 6c 20  -24:</i>.Fossil 
01b0: 68 61 73 20 62 65 65 6e 20 68 6f 73 74 69 6e 67  has been hosting
01c0: 20 69 74 73 65 6c 66 20 61 6e 64 20 73 65 76 65   itself and seve
01d0: 72 61 6c 20 6f 74 68 65 72 20 70 72 6f 6a 65 63  ral other projec
01e0: 74 73 20 66 6f 72 0a 6d 6f 6e 74 68 73 20 6e 6f  ts for.months no
01f0: 77 2e 20 20 4d 61 6e 79 20 62 75 67 73 20 68 61  w.  Many bugs ha
0200: 76 65 20 62 65 65 6e 20 65 6e 63 6f 75 6e 74 65  ve been encounte
0210: 72 65 64 2e 20 20 42 75 74 2c 20 74 68 61 6e 6b  red.  But, thank
0220: 73 20 69 6e 20 6c 61 72 67 65 0a 70 61 72 74 20  s in large.part 
0230: 74 6f 20 74 68 65 20 64 65 66 65 6e 73 69 76 65  to the defensive
0240: 20 6d 65 61 73 75 72 65 73 20 64 65 73 63 72 69   measures descri
0250: 62 65 64 20 68 65 72 65 2c 20 6e 6f 20 64 61 74  bed here, no dat
0260: 61 20 68 61 73 20 62 65 65 6e 0a 6c 6f 73 74 2e  a has been.lost.
0270: 20 20 54 68 65 20 69 6e 74 65 67 72 69 74 79 20    The integrity 
0280: 63 68 65 63 6b 73 20 61 72 65 20 64 6f 69 6e 67  checks are doing
0290: 20 74 68 65 69 72 20 6a 6f 62 20 77 65 6c 6c 2e   their job well.
02a0: 3c 2f 70 3e 0a 0a 3c 68 32 3e 41 74 6f 6d 69 63  </p>..<h2>Atomic
02b0: 20 43 68 65 63 6b 2d 69 6e 73 20 57 69 74 68 20   Check-ins With 
02c0: 52 6f 6c 6c 62 61 63 6b 3c 2f 68 32 3e 0a 0a 3c  Rollback</h2>..<
02d0: 70 3e 0a 54 68 65 20 66 6f 73 73 69 6c 20 72 65  p>.The fossil re
02e0: 70 6f 73 69 74 6f 72 79 20 69 73 20 61 6e 0a 3c  pository is an.<
02f0: 61 20 68 72 65 66 3d 22 68 74 74 70 3a 2f 2f 77  a href="http://w
0300: 77 77 2e 73 71 6c 69 74 65 2e 6f 72 67 2f 22 3e  ww.sqlite.org/">
0310: 53 51 4c 69 74 65 20 76 65 72 73 69 6f 6e 20 33  SQLite version 3
0320: 3c 2f 61 3e 20 64 61 74 61 62 61 73 65 20 66 69  </a> database fi
0330: 6c 65 2e 20 20 0a 53 51 4c 69 74 65 20 69 73 20  le.  .SQLite is 
0340: 76 65 72 79 20 6d 61 74 75 72 65 20 61 6e 64 20  very mature and 
0350: 73 74 61 62 6c 65 20 61 6e 64 20 68 61 73 20 62  stable and has b
0360: 65 65 6e 20 69 6e 20 77 69 64 65 2d 73 70 72 65  een in wide-spre
0370: 61 64 20 75 73 65 20 66 6f 72 20 6d 61 6e 79 0a  ad use for many.
0380: 79 65 61 72 73 2c 20 73 6f 20 77 65 20 68 61 76  years, so we hav
0390: 65 20 6c 69 74 74 6c 65 20 77 6f 72 72 69 65 73  e little worries
03a0: 20 74 68 61 74 20 69 74 20 6d 69 67 68 74 20 63   that it might c
03b0: 61 75 73 65 20 72 65 70 6f 73 69 74 6f 72 79 0a  ause repository.
03c0: 63 6f 72 72 75 70 74 69 6f 6e 2e 20 20 53 51 4c  corruption.  SQL
03d0: 69 74 65 0a 64 61 74 61 62 61 73 65 73 20 64 6f  ite.databases do
03e0: 20 6e 6f 74 20 63 6f 72 72 75 70 74 20 65 76 65   not corrupt eve
03f0: 6e 20 69 66 20 61 20 70 72 6f 67 72 61 6d 20 6f  n if a program o
0400: 72 20 73 79 73 74 65 6d 20 63 72 61 73 68 20 6f  r system crash o
0410: 72 20 70 6f 77 65 72 0a 66 61 69 6c 75 72 65 20  r power.failure 
0420: 6f 63 63 75 72 73 20 69 6e 20 74 68 65 20 6d 69  occurs in the mi
0430: 64 64 6c 65 20 6f 66 20 74 68 65 20 75 70 64 61  ddle of the upda
0440: 74 65 2e 20 20 49 66 20 73 6f 6d 65 20 6b 69 6e  te.  If some kin
0450: 64 20 6f 66 20 63 72 61 73 68 0a 64 6f 65 73 20  d of crash.does 
0460: 6f 63 63 75 72 20 69 6e 20 74 68 65 20 6d 69 64  occur in the mid
0470: 64 6c 65 20 6f 66 20 61 20 63 68 61 6e 67 65 2c  dle of a change,
0480: 20 74 68 65 6e 20 61 6c 6c 20 74 68 65 20 63 68   then all the ch
0490: 61 6e 67 65 73 20 61 72 65 20 72 6f 6c 6c 65 64  anges are rolled
04a0: 0a 62 61 63 6b 20 74 68 65 20 6e 65 78 74 20 74  .back the next t
04b0: 69 6d 65 20 74 68 61 74 20 74 68 65 20 64 61 74  ime that the dat
04c0: 61 62 61 73 65 20 69 73 20 61 63 63 65 73 73 65  abase is accesse
04d0: 64 2e 0a 3c 2f 70 3e 0a 0a 3c 70 3e 0a 41 20 63  d..</p>..<p>.A c
04e0: 68 65 63 6b 2d 69 6e 20 6f 70 65 72 61 74 69 6f  heck-in operatio
04f0: 6e 20 69 6e 20 66 6f 73 73 69 6c 20 6d 61 6b 65  n in fossil make
0500: 73 20 6d 61 6e 79 20 63 68 61 6e 67 65 73 20 74  s many changes t
0510: 6f 20 74 68 65 20 72 65 70 6f 73 69 74 6f 72 79  o the repository
0520: 0a 64 61 74 61 62 61 73 65 2e 20 20 42 75 74 20  .database.  But 
0530: 61 6c 6c 20 74 68 65 73 65 20 63 68 61 6e 67 65  all these change
0540: 73 20 68 61 70 70 65 6e 20 77 69 74 68 69 6e 20  s happen within 
0550: 61 20 73 69 6e 67 6c 65 20 74 72 61 6e 73 61 63  a single transac
0560: 74 69 6f 6e 2e 0a 49 66 20 73 6f 6d 65 74 68 69  tion..If somethi
0570: 6e 67 20 67 6f 65 73 20 77 72 6f 6e 67 20 69 6e  ng goes wrong in
0580: 20 74 68 65 20 6d 69 64 64 6c 65 20 6f 66 20 74   the middle of t
0590: 68 65 20 63 6f 6d 6d 69 74 2c 20 74 68 65 6e 20  he commit, then 
05a0: 74 68 65 20 74 72 61 6e 73 61 63 74 69 6f 6e 0a  the transaction.
05b0: 69 73 20 72 6f 6c 6c 65 64 20 62 61 63 6b 20 61  is rolled back a
05c0: 6e 64 20 74 68 65 20 64 61 74 61 62 61 73 65 20  nd the database 
05d0: 69 73 20 75 6e 63 68 61 6e 67 65 64 2e 0a 3c 2f  is unchanged..</
05e0: 70 3e 0a 0a 3c 68 32 3e 56 65 72 69 66 69 63 61  p>..<h2>Verifica
05f0: 74 69 6f 6e 20 4f 66 20 44 65 6c 74 61 20 45 6e  tion Of Delta En
0600: 63 6f 64 69 6e 67 73 20 50 72 69 6f 72 20 54 6f  codings Prior To
0610: 20 54 72 61 6e 73 61 63 74 69 6f 6e 20 43 6f 6d   Transaction Com
0620: 6d 69 74 3c 2f 68 32 3e 0a 0a 3c 70 3e 0a 54 68  mit</h2>..<p>.Th
0630: 65 20 63 6f 6e 74 65 6e 74 20 66 69 6c 65 73 20  e content files 
0640: 74 68 61 74 20 63 6f 6d 70 72 69 73 65 20 74 68  that comprise th
0650: 65 20 67 6c 6f 62 61 6c 20 73 74 61 74 65 20 6f  e global state o
0660: 66 20 61 20 66 6f 73 73 69 6c 20 72 65 73 70 6f  f a fossil respo
0670: 73 69 74 6f 72 79 0a 61 72 65 20 73 74 6f 72 65  sitory.are store
0680: 64 20 69 6e 20 74 68 65 20 72 65 70 6f 73 69 74  d in the reposit
0690: 6f 72 79 20 61 73 20 61 20 74 72 65 65 2e 20 20  ory as a tree.  
06a0: 54 68 65 20 6c 65 61 76 65 73 20 6f 66 20 74 68  The leaves of th
06b0: 65 20 74 72 65 65 20 61 72 65 0a 73 74 6f 72 65  e tree are.store
06c0: 64 20 61 73 20 7a 6c 69 62 2d 63 6f 6d 70 72 65  d as zlib-compre
06d0: 73 73 65 64 20 42 4c 4f 42 73 2e 20 20 49 6e 74  ssed BLOBs.  Int
06e0: 65 72 69 6f 72 20 6e 6f 64 65 73 20 61 72 65 20  erior nodes are 
06f0: 64 65 6c 74 61 73 20 66 72 6f 6d 20 74 68 65 69  deltas from thei
0700: 72 0a 64 65 63 65 6e 64 61 6e 74 73 2e 20 20 41  r.decendants.  A
0710: 20 6c 6f 74 20 6f 66 20 65 6e 63 6f 64 69 6e 67   lot of encoding
0720: 20 69 73 20 67 6f 69 6e 67 20 6f 6e 2e 20 20 54   is going on.  T
0730: 68 65 72 65 20 69 73 0a 7a 6c 69 62 2d 63 6f 6d  here is.zlib-com
0740: 70 72 65 73 73 69 6f 6e 20 77 68 69 63 68 20 69  pression which i
0750: 73 20 72 65 6c 61 74 69 76 65 6c 79 20 77 65 6c  s relatively wel
0760: 6c 2d 74 65 73 74 65 64 20 62 75 74 20 73 74 69  l-tested but sti
0770: 6c 6c 20 6d 69 67 68 74 0a 63 61 75 73 65 20 63  ll might.cause c
0780: 6f 72 72 75 70 74 69 6f 6e 20 69 66 20 75 73 65  orruption if use
0790: 64 20 69 6d 70 72 6f 70 65 72 6c 79 2e 20 20 41  d improperly.  A
07a0: 6e 64 20 74 68 65 72 65 20 69 73 20 74 68 65 20  nd there is the 
07b0: 72 65 6c 61 74 69 76 65 6c 79 0a 6e 65 77 20 64  relatively.new d
07c0: 65 6c 74 61 2d 65 6e 63 6f 64 69 6e 67 20 6d 65  elta-encoding me
07d0: 63 68 61 6e 69 73 6d 20 64 65 73 69 67 6e 65 64  chanism designed
07e0: 20 65 78 70 72 65 73 73 6c 79 20 66 6f 72 20 66   expressly for f
07f0: 6f 73 73 69 6c 2e 20 20 57 65 20 77 61 6e 74 0a  ossil.  We want.
0800: 74 6f 20 6d 61 6b 65 20 73 75 72 65 20 74 68 61  to make sure tha
0810: 74 20 62 75 67 73 20 69 6e 20 74 68 65 73 65 20  t bugs in these 
0820: 65 6e 63 6f 64 69 6e 67 20 6d 65 63 68 61 6e 69  encoding mechani
0830: 73 6d 73 20 64 6f 20 6e 6f 74 20 6c 65 61 64 20  sms do not lead 
0840: 74 6f 0a 6c 6f 73 73 20 6f 66 20 64 61 74 61 2e  to.loss of data.
0850: 0a 3c 2f 70 3e 0a 0a 3c 70 3e 0a 54 6f 20 69 6e  .</p>..<p>.To in
0860: 63 72 65 61 73 65 20 6f 75 72 20 63 6f 6e 66 69  crease our confi
0870: 64 65 6e 63 65 20 74 68 61 74 20 65 76 65 72 79  dence that every
0880: 74 68 69 6e 67 20 69 6e 20 74 68 65 20 72 65 70  thing in the rep
0890: 6f 73 69 74 6f 72 79 20 69 73 0a 72 65 63 6f 76  ository is.recov
08a0: 65 72 61 62 6c 65 2c 20 66 6f 73 73 69 6c 20 6d  erable, fossil m
08b0: 61 6b 65 73 20 73 75 72 65 20 69 74 20 63 61 6e  akes sure it can
08c0: 20 65 78 74 72 61 63 74 20 61 6e 20 65 78 61 63   extract an exac
08d0: 74 20 72 65 70 6c 69 63 61 74 65 0a 6f 66 20 65  t replicate.of e
08e0: 76 65 72 79 20 63 6f 6e 74 65 6e 74 20 66 69 6c  very content fil
08f0: 65 20 74 68 61 74 20 69 74 20 63 68 61 6e 67 65  e that it change
0900: 73 20 6a 75 73 74 20 70 72 69 6f 72 20 74 6f 20  s just prior to 
0910: 74 72 61 6e 73 61 63 74 69 6f 6e 0a 63 6f 6d 6d  transaction.comm
0920: 69 74 2e 20 20 53 6f 20 64 75 72 69 6e 67 20 74  it.  So during t
0930: 68 65 20 63 6f 75 72 73 65 20 6f 66 20 63 68 65  he course of che
0940: 63 6b 2d 69 6e 20 28 6f 72 20 6f 74 68 65 72 20  ck-in (or other 
0950: 72 65 70 6f 73 69 74 6f 72 79 0a 6f 70 65 72 61  repository.opera
0960: 74 69 6f 6e 29 20 6d 61 6e 79 20 64 69 66 66 65  tion) many diffe
0970: 72 65 6e 74 20 66 69 6c 65 73 0a 69 6e 20 74 68  rent files.in th
0980: 65 20 72 65 70 6f 73 69 74 6f 72 79 20 6d 69 67  e repository mig
0990: 68 74 20 62 65 20 6d 6f 64 69 66 69 65 64 2e 20  ht be modified. 
09a0: 20 53 6f 6d 65 20 66 69 6c 65 73 20 61 72 65 20   Some files are 
09b0: 73 69 6d 70 6c 79 0a 63 6f 6d 70 72 65 73 73 65  simply.compresse
09c0: 64 2e 20 20 4f 74 68 65 72 20 66 69 6c 65 73 20  d.  Other files 
09d0: 61 72 65 20 64 65 6c 74 61 20 65 6e 63 6f 64 65  are delta encode
09e0: 64 20 61 6e 64 20 74 68 65 6e 20 63 6f 6d 70 72  d and then compr
09f0: 65 73 73 65 64 2e 0a 57 68 69 6c 65 20 61 6c 6c  essed..While all
0a00: 20 74 68 69 73 20 69 73 20 67 6f 69 6e 67 20 6f   this is going o
0a10: 6e 2c 20 66 6f 73 73 69 6c 20 6d 61 6b 65 73 20  n, fossil makes 
0a20: 61 20 72 65 63 6f 72 64 20 6f 66 20 65 76 65 72  a record of ever
0a30: 79 20 66 69 6c 65 0a 74 68 61 74 20 69 73 20 65  y file.that is e
0a40: 6e 63 6f 64 65 64 20 61 6e 64 20 74 68 65 20 53  ncoded and the S
0a50: 48 41 31 20 68 61 73 68 20 6f 66 20 74 68 65 20  HA1 hash of the 
0a60: 6f 72 69 67 69 6e 61 6c 20 63 6f 6e 74 65 6e 74  original content
0a70: 20 6f 66 20 74 68 61 74 0a 66 69 6c 65 2e 20 20   of that.file.  
0a80: 54 68 65 6e 20 6a 75 73 74 20 62 65 66 6f 72 65  Then just before
0a90: 20 74 72 61 6e 73 61 63 74 69 6f 6e 20 63 6f 6d   transaction com
0aa0: 6d 69 74 2c 20 66 6f 73 73 69 6c 20 72 65 2d 65  mit, fossil re-e
0ab0: 78 74 72 61 63 74 73 0a 74 68 65 20 6f 72 69 67  xtracts.the orig
0ac0: 69 6e 61 6c 20 63 6f 6e 74 65 6e 74 20 6f 66 20  inal content of 
0ad0: 61 6c 6c 20 66 69 6c 65 73 20 74 68 61 74 20 77  all files that w
0ae0: 65 72 65 20 77 72 69 74 74 65 6e 2c 20 63 6f 6d  ere written, com
0af0: 70 75 74 65 73 0a 74 68 65 20 53 48 41 31 20 63  putes.the SHA1 c
0b00: 68 65 63 6b 73 75 6d 20 61 67 61 69 6e 2c 20 61  hecksum again, a
0b10: 6e 64 20 76 65 72 69 66 69 65 73 20 74 68 61 74  nd verifies that
0b20: 20 74 68 65 20 63 68 65 63 6b 73 75 6d 73 20 6d   the checksums m
0b30: 61 74 63 68 2e 0a 49 66 20 61 6e 79 74 68 69 6e  atch..If anythin
0b40: 67 20 64 6f 65 73 20 6e 6f 74 20 6d 61 74 63 68  g does not match
0b50: 20 75 70 2c 20 61 6e 20 65 72 72 6f 72 0a 6d 65   up, an error.me
0b60: 73 73 61 67 65 20 69 73 20 70 72 69 6e 74 65 64  ssage is printed
0b70: 20 61 6e 64 20 74 68 65 20 74 72 61 6e 73 61 63   and the transac
0b80: 74 69 6f 6e 20 72 6f 6c 6c 73 20 62 61 63 6b 2e  tion rolls back.
0b90: 0a 3c 2f 70 3e 0a 0a 3c 70 3e 0a 53 6f 2c 20 69  .</p>..<p>.So, i
0ba0: 6e 20 6f 74 68 65 72 20 77 6f 72 64 73 2c 20 66  n other words, f
0bb0: 6f 73 73 69 6c 20 61 6c 77 61 79 73 20 63 68 65  ossil always che
0bc0: 63 6b 73 20 74 6f 20 6d 61 6b 65 20 73 75 72 65  cks to make sure
0bd0: 20 69 74 20 63 61 6e 0a 72 65 2d 65 78 74 72 61   it can.re-extra
0be0: 63 74 20 61 20 66 69 6c 65 20 62 65 66 6f 72 65  ct a file before
0bf0: 20 69 74 20 63 6f 6d 6d 69 74 73 20 61 20 63 68   it commits a ch
0c00: 61 6e 67 65 20 74 6f 20 74 68 61 74 20 66 69 6c  ange to that fil
0c10: 65 2e 0a 48 65 6e 63 65 20 62 75 67 73 20 69 6e  e..Hence bugs in
0c20: 20 66 6f 73 73 69 6c 20 61 72 65 20 75 6e 6c 69   fossil are unli
0c30: 6b 65 6c 79 20 74 6f 20 63 6f 72 72 75 70 74 20  kely to corrupt 
0c40: 74 68 65 20 72 65 70 6f 73 69 74 6f 72 79 20 69  the repository i
0c50: 6e 0a 61 20 77 61 79 20 74 68 61 74 20 70 72 65  n.a way that pre
0c60: 76 65 6e 74 73 20 75 73 20 66 72 6f 6d 20 65 78  vents us from ex
0c70: 74 72 61 63 74 69 6e 67 20 68 69 73 74 6f 72 69  tracting histori
0c80: 63 61 6c 20 76 65 72 73 69 6f 6e 73 20 6f 66 20  cal versions of 
0c90: 0a 66 69 6c 65 73 2e 0a 3c 2f 70 3e 0a 0a 3c 68  .files..</p>..<h
0ca0: 32 3e 43 68 65 63 6b 73 75 6d 20 4f 76 65 72 20  2>Checksum Over 
0cb0: 41 6c 6c 20 46 69 6c 65 73 20 49 6e 20 41 20 42  All Files In A B
0cc0: 61 73 65 6c 69 6e 65 3c 2f 68 32 3e 0a 0a 3c 70  aseline</h2>..<p
0cd0: 3e 0a 4d 61 6e 69 66 65 73 74 20 61 72 74 69 66  >.Manifest artif
0ce0: 61 63 74 73 20 74 68 61 74 20 64 65 66 69 6e 65  acts that define
0cf0: 20 61 20 62 61 73 65 6c 69 6e 65 20 68 61 76 65   a baseline have
0d00: 20 74 77 6f 20 66 69 65 6c 64 73 20 28 74 68 65   two fields (the
0d10: 0a 52 2d 63 61 72 64 20 61 6e 64 20 5a 2d 63 61  .R-card and Z-ca
0d20: 72 64 29 20 74 68 61 74 20 72 65 63 6f 72 64 20  rd) that record 
0d30: 4d 44 35 20 68 61 73 68 73 20 6f 66 20 74 68 65  MD5 hashs of the
0d40: 20 6d 61 6e 69 66 65 73 74 20 69 74 73 65 6c 66   manifest itself
0d50: 0a 61 6e 64 20 6f 66 20 61 6c 6c 20 6f 74 68 65  .and of all othe
0d60: 72 20 66 69 6c 65 73 20 69 6e 20 74 68 65 20 6d  r files in the m
0d70: 61 6e 69 66 65 73 74 2e 20 20 50 72 69 6f 72 20  anifest.  Prior 
0d80: 74 6f 20 61 6e 79 20 63 68 65 63 6b 2d 69 6e 0a  to any check-in.
0d90: 63 6f 6d 6d 69 74 2c 20 74 68 65 73 65 20 63 68  commit, these ch
0da0: 65 63 6b 73 75 6d 73 20 61 72 65 20 76 65 72 69  ecksums are veri
0db0: 66 69 65 64 20 74 6f 20 65 6e 73 75 72 65 20 74  fied to ensure t
0dc0: 68 61 74 20 74 68 65 20 62 61 73 65 6c 69 6e 65  hat the baseline
0dd0: 0a 63 68 65 63 6b 65 64 20 69 6e 20 61 67 72 65  .checked in agre
0de0: 65 73 20 65 78 61 63 74 6c 79 20 77 69 74 68 20  es exactly with 
0df0: 77 68 61 74 20 69 73 20 6f 6e 20 64 69 73 6b 2e  what is on disk.
0e00: 20 20 53 69 6d 69 6c 61 72 6c 79 2c 0a 74 68 65    Similarly,.the
0e10: 20 72 65 70 6f 73 69 74 6f 72 79 20 63 68 65 63   repository chec
0e20: 6b 73 75 6d 20 69 73 20 76 65 72 69 66 69 65 64  ksum is verified
0e30: 20 61 66 74 65 72 20 61 20 63 68 65 63 6b 6f 75   after a checkou
0e40: 74 20 74 6f 20 6d 61 6b 65 0a 73 75 72 65 20 74  t to make.sure t
0e50: 68 61 74 20 74 68 65 20 65 6e 74 69 72 65 20 72  hat the entire r
0e60: 65 70 6f 73 69 74 6f 72 79 20 77 61 73 20 63 68  epository was ch
0e70: 65 63 6b 65 64 20 6f 75 74 20 63 6f 72 72 65 63  ecked out correc
0e80: 74 6c 79 2e 0a 4e 6f 74 65 20 74 68 61 74 20 74  tly..Note that t
0e90: 68 65 73 65 20 61 64 64 65 64 20 63 68 65 63 6b  hese added check
0ea0: 73 20 75 73 65 20 61 20 64 69 66 66 65 72 65 6e  s use a differen
0eb0: 74 20 68 61 73 68 20 28 4d 44 35 20 69 6e 73 74  t hash (MD5 inst
0ec0: 65 61 64 0a 6f 66 20 53 48 41 31 29 20 69 6e 20  ead.of SHA1) in 
0ed0: 6f 72 64 65 72 20 74 6f 20 61 76 6f 69 64 20 63  order to avoid c
0ee0: 6f 6d 6d 6f 6e 2d 6d 6f 64 65 20 66 61 69 6c 75  ommon-mode failu
0ef0: 72 65 73 20 69 6e 20 74 68 65 20 68 61 73 68 0a  res in the hash.
0f00: 61 6c 67 6f 72 69 74 68 6d 20 69 6d 70 6c 65 6d  algorithm implem
0f10: 65 6e 74 61 74 69 6f 6e 2e 0a 3c 2f 70 3e 0a     entation..</p>.