view release on metacpan or  search on metacpan

src/subversion/subversion/libsvn_fs_base/notes/structure  view on Meta::CPAN

         - (1) E exists in both ANCESTOR and B, and refers to the same
           node revision.  Replace E with A's node revision.  ***
       - (1) E exists in both ANCESTOR and A, and refers to the same
         node revision.
         - (1) E exists in both ANCESTOR and B, and refers to the same
           node revision.  Nothing has happened to ANCESTOR/E, so no
           change is necessary.
   
   *** == something actually happens


Non-Historical Properties

[[Yes, do tell.]]


UUIDs: Universally Unique Identifiers

Every filesystem has a UUID.  This is represented as record #1 in the
`uuids' table.


Layers

In previous structurings of the code, I had trouble keeping track of
exactly who has implemented which promises, based on which other
promises from whom.

I hope the arrangement below will help me keep things straight, and
make the code more reliable.  The files are arranged in order from
low-level to high-level: each file depends only on services provided
by the files before it.

skel.c, id.c, dbt.c, convert-size.c

                Low-level utility functions.

fs_skels.c      Routines for marshaling between skels and native FS types.

fs.c            Creating and destroying filesystem objects.

err.c           Error handling.

nodes-table.c, txn-table.c, rev-table.c, reps-table.c, strings-table.c

                Create and open particular database tables.
                Responsible for intra-record consistency.

node-rev.c      Creating, reading, and writing node revisions.
                Responsible for deciding what gets deltified when.

reps-strings.c
                Retrieval and storage of represented strings.
                This will handle delta-based storage,

dag.c           Operations on the DAG filesystem.  "DAG" because the
                interface exposes the filesystem's sharing structure.
                Enforce inter-record consistency.

tree.c          Operations on the tree filesystem.  This layer is
                built on top of dag.c, but transparently distinguishes
                virtual copies, making the underlying DAG look like a
                real tree.  This makes incomplete transactions behave
                like ordinary mutable filesystems.

delta.c         Computing deltas.



Appendix: Filesystem structure summary
======================================

Berkeley DB tables
------------------

                "nodes" : btree(ID -> NODE-REVISION, "next-key" -> NODE-ID)
            "revisions" : recno(REVISION)
         "transactions" : btree(TXN -> TRANSACTION, "next-key" -> TXN)
              "changes" : btree(TXN -> CHANGE)
               "copies" : btree(CPY -> COPY, "next-key" -> CPY)
              "strings" : btree(STR -> STRING, "next-key" -> STR)
      "representations" : btree(REP -> REPRESENTATION, "next-key" -> REP)
                "uuids" : recno(UUID)
                "locks" : btree(TOKEN -> LOCK)
          "lock-tokens" : btree(PATH -> TOKEN)
         "node-origins" : btree(NODE-ID -> ID)
        "checksum-reps" : btree(SHA1SUM -> REP, "next-key" -> number-36)
        "miscellaneous" : btree(STRING -> STRING)

Syntactic elements
------------------

Table keys:

                     ID ::= NODE-REV-ID ;
                    TXN ::= number-36 ;
                    CPY ::= number-36 ;
                    STR ::= number-36 ;
                    REP ::= number-36 ;
                  TOKEN ::= uuid ;

Property lists:

               PROPLIST ::= (PROP ...) ;
                   PROP ::= atom atom ;


Filesystem revisions:

               REVISION ::= ("revision" TXN) ;


Transactions:

            TRANSACTION ::= UNFINISHED-TXN | COMMITTED-TXN | DEAD-TXN
         UNFINISHED-TXN ::= ("transaction" ROOT-ID BASE-ID PROPLIST COPIES) ;
          COMMITTED-TXN ::= ("committed" ROOT-ID REV PROPLIST COPIES) ;
               DEAD-TXN ::= ("dead" ROOT-ID BASE-ID PROPLIST COPIES) ;
                ROOT-ID ::= NODE-REV-ID ;
                BASE-ID ::= NODE-REV-ID ;
                 COPIES ::= (CPY ...) ;