[sqlite] Remove obsolete reference version 3.8.7.4.

third_party/sqlite/sqlite-src-3080704/doc/pager-invariants.txt

- *** Throughout this document, a page is deemed to have been synced
-     automatically as soon as it is written when PRAGMA synchronous=OFF.
-     Otherwise, the page is not synced until the xSync method of the VFS
-     is called successfully on the file containing the page.
-
- *** Definition:  A page of the database file is said to be "overwriteable" if
-     one or more of the following are true about the page:
- 
-     (a)  The original content of the page as it was at the beginning of
-          the transaction has been written into the rollback journal and
-          synced.
- 
-     (b)  The page was a freelist leaf page at the start of the transaction.
- 
-     (c)  The page number is greater than the largest page that existed in
-          the database file at the start of the transaction.
- 
- (1) A page of the database file is never overwritten unless one of the
-     following are true:
- 
-     (a) The page and all other pages on the same sector are overwriteable.
- 
-     (b) The atomic page write optimization is enabled, and the entire
-         transaction other than the update of the transaction sequence
-         number consists of a single page change.
- 
- (2) The content of a page written into the rollback journal exactly matches
-     both the content in the database when the rollback journal was written
-     and the content in the database at the beginning of the current
-     transaction.
- 
- (3) Writes to the database file are an integer multiple of the page size
-     in length and are aligned to a page boundary.
- 
- (4) Reads from the database file are either aligned on a page boundary and
-     an integer multiple of the page size in length or are taken from the
-     first 100 bytes of the database file.
- 
- (5) All writes to the database file are synced prior to the rollback journal
-     being deleted, truncated, or zeroed.
- 
- (6) If a master journal file is used, then all writes to the database file
-     are synced prior to the master journal being deleted.
- 
- *** Definition: Two databases (or the same database at two points it time)
-     are said to be "logically equivalent" if they give the same answer to
-     all queries.  Note in particular the content of freelist leaf
-     pages can be changed arbitarily without effecting the logical equivalence
-     of the database.
- 
- (7) At any time, if any subset, including the empty set and the total set,
-     of the unsynced changes to a rollback journal are removed and the 
-     journal is rolled back, the resulting database file will be logical
-     equivalent to the database file at the beginning of the transaction.
- 
- (8) When a transaction is rolled back, the xTruncate method of the VFS
-     is called to restore the database file to the same size it was at
-     the beginning of the transaction.  (In some VFSes, the xTruncate
-     method is a no-op, but that does not change the fact the SQLite will
-     invoke it.)
- 
- (9) Whenever the database file is modified, at least one bit in the range
-     of bytes from 24 through 39 inclusive will be changed prior to releasing
-     the EXCLUSIVE lock.
-
-(10) The pattern of bits in bytes 24 through 39 shall not repeat in less
-     than one billion transactions.
-
-(11) A database file is well-formed at the beginning and at the conclusion
-     of every transaction.
-
-(12) An EXCLUSIVE lock must be held on the database file before making
-     any changes to the database file.
-
-(13) A SHARED lock must be held on the database file before reading any
-     content out of the database file.