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* Update oslo.db from branch 'master'
  to 009d23df45969036c70e4cf59eb4019aaace9a55
  - Add option for wsrep_sync_wait
    
    When using Galera, the wsrep_sync_wait option [1]
    can change the behavior of a variety of Galera DQL/DML statements
    such that a particular operation will pause until outstanding
    write-sets are fully persisted to the local node.  The setting
    supersedes the previous boolean parameter wsrep_causal_reads
    which only affected SELECT, with an updated approach that allows
    for fine-grained control of so-called "causality checks"
    on individual statement types.  The legacy-compatible setting
    of '1' indicates that READ/SELECT/BEGIN operations should
    proceed only after any pending writesets are fully available.
    
    The use case for this setting is for an application that
    is running operations on multiple Galera nodes simultaenously.
    An application that commits data on one node, and then immediately
    uses a different connection (on a potentially different node)
    to SELECT that data, may fail to see those changes if
    "causality checks" for SELECT are not enabled.  While
    a COMMIT operation in Galera will block locally until all other
    nodes approve of the writeset, the operation does not block
    for the subsequent period of time when other nodes are actually
    persisting that writeset.  Setting up "causal reads"
    in this case indicates that a SELECT operation will wait until
    any writesets in progress are available, thus maintaining
    serialization between the COMMIT and subsequent SELECT.
    
    As the name implies, wsrep_sync_wait adds...waiting!  to the
    operation, and thus directly impacts performance by adding
    latency to SELECT operations or to the operations that have
    been selected for causality checks, to the degree that
    concurrent writesets are expected to be present.
    
    Since it's not expected that most if any Openstack applications
    actually need this setting in order to be effective with
    Galera multi-master operation, and as the setting is available
    within client session scope and also impacts performance,
    making it available on a per-application basis means that
    specific applications which may see issues under load can
    choose to enable this setting, much in the way any other
    "transaction isolation" settings might be made, without having
    to add a cluster-wide performance penalty by setting it at the
    Galera server level.
    
    [1] https://mariadb.com/docs/ent/ref/mdb/system-variables/wsrep_sync_wait/
    
    Change-Id: Iee7afcac8ba952a2d67a9ad9dd0e4eae3f42518e
This commit is contained in:
Mike Bayer 2022-12-08 08:40:13 -05:00 committed by Gerrit Code Review
parent 14da0e651e
commit 61cf391ae8
1 changed files with 1 additions and 1 deletions
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oslo.db

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Subproject commit a191d2e629f55c999b37a7a795ad6fbee2807b98
Subproject commit 009d23df45969036c70e4cf59eb4019aaace9a55