[arch-dev-public] [signoff] sqlite3 - 188.8.131.52-1
a.radke at arcor.de
Thu May 19 15:37:50 EDT 2011
Minor upstream release. Please give signoffs.
2011-May-19 - Version 184.108.40.206
SQLite version 220.127.116.11 is a patch release that fixes a single bug
associated with WAL mode. The bug has been in SQLite ever since WAL
was added, but the problem is very obscure and so nobody has
noticed before now. Nevertheless, all users are encouraged to
upgrade to version 18.104.22.168 or later.
The bug is this: If the cache_size is set very small (less than 10)
and SQLite comes under memory pressure and if a multi-statement
transaction is started in which the last statement prior to COMMIT
is a SELECT statement and if a checkpoint occurs right after the
transaction commit, then it might happen that the transaction will
be silently rolled back instead of being committed.
The default setting for cache_size is 2000. So in most situations,
this bug will never appear. But sometimes programmers set
cache_size to very small values on gadgets and other low-memory
devices in order to save memory space. Such applications are
vulnerable. Note that this bug does not cause database corruption.
It is as if ROLLBACK were being run instead of COMMIT in some cases.
Transactions commit in WAL mode by adding a record onto the end of
the WAL (the write-ahead log) that contains a "commit" flag. So to
commit a transaction, SQLite takes all the pages that have changed
during that transaction, appends them to the WAL, and sets the
commit flag on the last page. Now, if SQLite comes under memory
pressure, it might try to free up memory space by writing changed
pages to the WAL prior to the commit. We call this "spilling" the
cache to WAL. There is nothing wrong with spilling cache to WAL.
But if the memory pressure is severe, it might be that by the time
COMMIT is run, all changed pages for the transaction have already
been spilled to WAL and there are no pages left to be written to
WAL. And with no unwritten pages, there was nothing to put the
commit flag on. And without a commit flag, the transaction would
end up being rolled back.
The fix to this problem was that if all changed pages has already
been written to the WAL when the commit was started, then page 1 of
the database will be written to the WAL again, so that there will
always be a page available on which to set the commit flag.
2011-April-17 - Version 22.214.171.124
SQLite version 126.96.36.199 adds a one-line bug fix to 188.8.131.52 that
enables pthreads to work correctly on NetBSD. The problem was a
faulty function signature for the open system call. The problem
does not appear to have any adverse impact on any system other than
Upgrading from version 184.108.40.206 is only needed on NetBSD.
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