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Fix transactions once again
This commit is contained in:
Markus Unterwaditzer
parent
07f6c3af12
commit
fbe3f9910d
1 changed files with 59 additions and 52 deletions
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@ -25,6 +25,18 @@ from .utils import uniq
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sync_logger = logging.getLogger(__name__)
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@contextlib.contextmanager
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def _exclusive_transaction(conn):
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try:
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c = conn.execute('BEGIN EXCLUSIVE TRANSACTION')
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yield c
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c.execute('COMMIT')
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except BaseException:
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_, e, tb = sys.exc_info()
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c.execute('ROLLBACK')
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raise e.with_traceback(tb)
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class SyncError(exceptions.Error):
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'''Errors related to synchronization.'''
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@ -208,48 +220,47 @@ class SqliteStatus(_StatusBase):
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# If we ever bump the schema version, we will need a way to migrate
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# data.
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with _exclusive_transaction(self._c) as c:
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c.execute('CREATE TABLE meta ( "version" INTEGER PRIMARY KEY )')
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c.execute('INSERT INTO meta (version) VALUES (?)',
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(self.SCHEMA_VERSION,))
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self._c.execute('''CREATE TABLE meta (
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"version" INTEGER PRIMARY KEY
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); ''')
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self._c.execute('INSERT INTO meta (version) VALUES (?)',
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(self.SCHEMA_VERSION,))
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# I know that this is a bad schema, but right there is just too
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# little gain in deduplicating the .._a and .._b columns.
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c.execute('''CREATE TABLE status (
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"ident" TEXT PRIMARY KEY NOT NULL,
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"href_a" TEXT,
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"href_b" TEXT,
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"hash_a" TEXT NOT NULL,
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"hash_b" TEXT NOT NULL,
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"etag_a" TEXT,
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"etag_b" TEXT
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); ''')
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c.execute('CREATE UNIQUE INDEX by_href_a ON status(href_a)')
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c.execute('CREATE UNIQUE INDEX by_href_b ON status(href_b)')
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# I know that this is a bad schema, but right there is just too little
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# gain in deduplicating the .._a and .._b columns.
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self._c.execute('''CREATE TABLE status (
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"ident" TEXT PRIMARY KEY NOT NULL,
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"href_a" TEXT,
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"href_b" TEXT,
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"hash_a" TEXT NOT NULL,
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"hash_b" TEXT NOT NULL,
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"etag_a" TEXT,
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"etag_b" TEXT
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); ''')
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self._c.execute('CREATE UNIQUE INDEX by_href_a ON status(href_a)')
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self._c.execute('CREATE UNIQUE INDEX by_href_b ON status(href_b)')
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# We cannot add NOT NULL here because data is first fetched for the
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# storage a, then storage b. Inbetween the `_b`-columns are filled with
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# NULL.
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#
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# In an ideal world we would be able to start a transaction with one
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# cursor, write our new data into status and simultaneously query the
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# old status data using a different cursor. Unfortunately sqlite
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# enforces NOT NULL constraints immediately, not just at commit. Since
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# there is also no way to alter constraints on a table (disable
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# constraints on start of transaction and reenable on end), it's a
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# separate table now that just gets copied over before we commit.
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# That's a lot of copying, sadly.
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self._c.execute('''CREATE TABLE new_status (
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"ident" TEXT PRIMARY KEY NOT NULL,
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"href_a" TEXT,
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"href_b" TEXT,
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"hash_a" TEXT,
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"hash_b" TEXT,
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"etag_a" TEXT,
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"etag_b" TEXT
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); ''')
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# We cannot add NOT NULL here because data is first fetched for the
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# storage a, then storage b. Inbetween the `_b`-columns are filled
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# with NULL.
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#
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# In an ideal world we would be able to start a transaction with
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# one cursor, write our new data into status and simultaneously
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# query the old status data using a different cursor.
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# Unfortunately sqlite enforces NOT NULL constraints immediately,
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# not just at commit. Since there is also no way to alter
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# constraints on a table (disable constraints on start of
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# transaction and reenable on end), it's a separate table now that
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# just gets copied over before we commit. That's a lot of copying,
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# sadly.
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c.execute('''CREATE TABLE new_status (
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"ident" TEXT PRIMARY KEY NOT NULL,
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"href_a" TEXT,
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"href_b" TEXT,
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"hash_a" TEXT,
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"hash_b" TEXT,
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"etag_a" TEXT,
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"etag_b" TEXT
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); ''')
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def _is_latest_version(self):
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try:
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@ -262,19 +273,15 @@ class SqliteStatus(_StatusBase):
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@contextlib.contextmanager
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def transaction(self):
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old_c = self._c
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try:
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old_c = self._c
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self._c = self._c.execute('BEGIN EXCLUSIVE TRANSACTION')
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yield
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self._c.execute('DELETE FROM status')
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self._c.execute('INSERT INTO status '
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'SELECT * FROM new_status')
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self._c.execute('DELETE FROM new_status')
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self._c.execute('COMMIT')
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except BaseException:
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_, e, tb = sys.exc_info()
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self._c.execute('ROLLBACK')
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raise e.with_traceback(tb)
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with _exclusive_transaction(self._c) as new_c:
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self._c = new_c
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yield
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self._c.execute('DELETE FROM status')
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self._c.execute('INSERT INTO status '
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'SELECT * FROM new_status')
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self._c.execute('DELETE FROM new_status')
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finally:
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self._c = old_c
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