diff options
| author |  Joey Hess <joeyh@joeyh.name> | 2017-09-06 17:07:49 -0400 |
|---|---|---|
| committer | Joey Hess <joeyh@joeyh.name> | 2017-09-06 17:19:07 -0400 |
| commit | 087612ed842c060ee1749b5967a226708870546b (patch) | |
| tree | 807d15d0e8e1dcb3c7a9d940971956adf3b676bb /Database/Queue.hs | |
| parent | f69b019a04bbad2061ea3cfd069b502cdbcc8871 (diff) | |
fix consistency bug reading from export database
The export database has writes made to it and then expects to read back
the same data immediately. But, the way that Database.Handle does
writes, in order to support multiple writers, makes that not work, due
to caching issues. This resulted in export re-uploading files it had
already successfully renamed into place.
Fixed by allowing databases to be opened in MultiWriter or SingleWriter
mode. The export database only needs to support a single writer; it does
not make sense for multiple exports to run at the same time to the same
special remote.
All other databases still use MultiWriter mode. And by inspection,
nothing else in git-annex seems to be relying on being able to
immediately query for changes that were just written to the database.
This commit was supported by the NSF-funded DataLad project.
Diffstat (limited to 'Database/Queue.hs')
| -rw-r--r-- | Database/Queue.hs | 12 |
1 files changed, 8 insertions, 4 deletions
diff --git a/Database/Queue.hs b/Database/Queue.hs index 143871079..f0a2d2b65 100644 --- a/Database/Queue.hs +++ b/Database/Queue.hs @@ -9,6 +9,7 @@ module Database.Queue ( DbQueue, + DbConcurrency(..), openDbQueue, queryDbQueue, closeDbQueue, @@ -35,9 +36,9 @@ data DbQueue = DQ DbHandle (MVar Queue) {- Opens the database queue, but does not perform any migrations. Only use - if the database is known to exist and have the right tables; ie after - running initDb. -} -openDbQueue :: FilePath -> TableName -> IO DbQueue -openDbQueue db tablename = DQ - <$> openDb db tablename +openDbQueue :: DbConcurrency -> FilePath -> TableName -> IO DbQueue +openDbQueue dbconcurrency db tablename = DQ + <$> openDb dbconcurrency db tablename <*> (newMVar =<< emptyQueue) {- This or flushDbQueue must be called, eg at program exit to ensure @@ -60,8 +61,11 @@ flushDbQueue (DQ hdl qvar) = do {- Makes a query using the DbQueue's database connection. - This should not be used to make changes to the database! - - - Queries will not return changes that have been recently queued, + - Queries will not see changes that have been recently queued, - so use with care. + - + - Also, when the database was opened in MultiWriter mode, + - queries may not see changes even after flushDbQueue. -} queryDbQueue :: DbQueue -> SqlPersistM a -> IO a queryDbQueue (DQ hdl _) = queryDb hdl |