[Bugs] [Bug 1240577] Data Tiering: Database locks observed on tiered volumes on continous writes to a file

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1240577

Joseph Elwin Fernandes <josferna at redhat.com> changed:

           What    |Removed                     |Added
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                 CC|                            |josferna at redhat.com



--- Comment #1 from Joseph Elwin Fernandes <josferna at redhat.com> ---
The reason this happens is in WAL mode opening a new db connection is an
expensive operation as it will try to a lock on the WAL file(even though for a
short time). The migration process opens a new connection per brick per
promotion/demotion cycle. This is bad scheme.

Solution:
1) Create a new connection only in tier_init per brick and have the connection
alive and use it for every promotion/demotion 
2) Enable pooling (Pooling=True in the connection string) when the connection
is established, there isn't any locking of WAL file, because existing
connections are reused internal to sqlite.

http://dev.yorhel.nl/doc/sqlaccess

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