[
https://issues.apache.org/jira/browse/ARTEMIS-3340?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Francesco Nigro updated ARTEMIS-3340:
-------------------------------------
Description:
Shared-nothing replication can cause journal misalignment despite no
split-brain events.
There are several ways that can cause this to happen.
Below some scenario that won't involve network partitions/drastic outages.
Scenario 1:
# Master/Primary start as live, clients connect to it
# Backup become an in-sync replica
# User stop live and backup failover to it
# *Backup serve clients alone, modifying its journal*
# User stop backup
# User start master/primary: it become live with a journal misaligned to the
most up-to-date one ie on the stopped backup
Scenario 2:
# Master/Primary start as live, clients connect to it
# Backup become an in-sync replica
# Connection glitch between backup -> live
# backup start trying to failover (for {{vote-retries * vote-retry-wait}}
milliseconds)
# *Live serve clients alone, modifying its journal*
# User stop live
# Backup succeed to failover: it become live with a journal misaligned to the
most up-to-date one ie on the stopped live
The main cause of this issue is because we allow *a single broker to serve
clients*, despite configured with HA, generating the journal misalignment.
The quorum service (classic or pluggable) just take care of mutual exclusive
presence of broker for the live role (vs a NodeID), without considering live
role ordering based on the most up-to-date journal.
A possible solution is to use
https://issues.apache.org/jira/browse/ARTEMIS-2716 and use a quorum "logical
timestamp/version" marking the age/ownership changes of the journal in order to
force live to always have the most up-to-date journal. It means that such value
has to be locally saved and exchanged during the initial replica sync,
involving both journal data and core message protocol changes (just for the
replication channel, without impacting real clients).
In case of quorum service restart/outage, admin must use command/configuration
to let a broker to ignore the age of its journal and just force it to start.
In addition new journal CLI commands should be implemented to inspect the age
of a (local) broker journal or query/force the quorum journal version too, for
troubleshooting reasons.
It's very important to capture every possible event that cause the journal
age/ownership to change.
Now let's take a look at Scenario 2 with journal versioning/timestamp:
# live broker start because it matches the most up to date journal version,
increasing it (locally and remotely) when it become fully alive
# backup found it and trust that, given that's live, it already has the
most-up-to-date journal for a specific NodeID
# live broker send its journal files to the backup, along with its local
journal version
# backup is now ready to failover in any moment: it store the sent journal
version on its local storage
# network glitch happen
# backup try to become live for vote-retries times
# live detect replication disconnection and *increment the journal version*
(both quorum and local one)
# live serve clients alone, modifying its journal
# outage/stop cause live to die
# backup detect that *journal version no longer matching its own local journal
version*: it stop trying to become live
The key parts related to journal age/version are:
* only who's live can change quorum (and local) journal version (with a
monotonic increment)
* every ownership change event must cause journal age/version to change eg
starting as live, loosing its backup, etc etc
Re the RI implementation using Apache Curator, this could use a separate
[DistributedAtomicLong|https://curator.apache.org/apidocs/org/apache/curator/framework/recipes/atomic/DistributedAtomicLong.html]
to manage the journal version.
Although tempting, it's not a good idea to not just use the data field on
{{InterProcessSemaphoreV2}}, because:
* there's no API to query it if no lease is acquired yet (or created)
* we more need to "age" the journal independently from the lock
acquisition/release process eg a live that drop its replica need to increment
the journal version
Athough tempting, it's not a good idea to just use the last alive broker
connector identity instead of a journal version, because of the ABA problem
(see https://en.wikipedia.org/wiki/ABA_problem).
This versioning mechanism isn't without drawbacks: quorum journal versioning
requires to store a local copy of the version in order to allow the broker to
query and compare it with the quorum one on restart; having 2 separate and not
atomic operations means that there must be a way to reconcile/fix it in case of
misalignments. As said above, this could be done with admin operations.
Journal versioning change the way roles behave, but they still retain theirs
key characteristics:
- backup should try start as live in case it has the most up to date journal
and there is no other live around: differently, can just rotate journal and be
available to replicate some live
- primary try to fail-back to any existing live with the most up to date
journal or await it to appear, without becoming live if it doesn't have the
most up-to-date journal
This would ensure that If both broker are up and running and backup allow a
primary to failback, the primary eventually become live and backup replicates
it, preserving the desired broker roles.
was:
Shared-nothing replication can cause journal misalignment despite no
split-brain events.
There are several ways that can cause this to happen.
Below some scenario that won't involve network partitions/drastic outages.
Scenario 1:
# Master/Primary start as live, clients connect to it
# Backup become an in-sync replica
# User stop live and backup failover to it
# *Backup serve clients alone, modifying its journal*
# User stop backup
# User start master/primary: it become live with a journal misaligned to the
most up-to-date one ie on the stopped backup
Scenario 2:
# Master/Primary start as live, clients connect to it
# Backup become an in-sync replica
# Connection glitch between backup -> live
# backup start trying to failover (for {{vote-retries * vote-retry-wait}}
milliseconds)
# *Live serve clients alone, modifying its journal*
# User stop live
# Backup succeed to failover: it become live with a journal misaligned to the
most up-to-date one ie on the stopped live
The main cause of this issue is because we allow *a single broker to serve
clients*, despite configured with HA, generating the journal misalignment.
The quorum service (classic or pluggable) just take care of mutual exclusive
presence of broker for the live role (vs a NodeID), without considering live
role ordering based on the most up-to-date journal.
A possible solution is to use
https://issues.apache.org/jira/browse/ARTEMIS-2716 and use a quorum "logical
timestamp/version" marking the age/ownership changes of the journal in order to
force live to always have the most up-to-date journal. It means that such value
has to be locally saved and exchanged during the initial replica sync,
involving both journal data and core message protocol changes (just for the
replication channel, without impacting real clients).
In case of quorum service restart/outage, admin must use command/configuration
to let a broker to ignore the age of its journal and just force it to start.
In addition new journal CLI commands should be implemented to inspect the age
of a (local) broker journal or query/force the quorum journal version too, for
troubleshooting reasons.
It's very important to capture every possible event that cause the journal
age/ownership to change.
Now let's take a look at Scenario 2 with journal versioning/timestamp:
# live broker start because it matches the most up to date journal version,
increasing it (locally and remotely) when it become fully alive
# backup found it and trust that, given that's live, it already has the
most-up-to-date journal for a specific NodeID
# live broker send its journal files to the backup, along with its local
journal version
# backup is now ready to failover in any moment: it store the sent journal
version on its local storage
# network glitch happen
# backup try to become live for vote-retries times
# live detect replication disconnection and *increment the journal version*
(both quorum and local one)
# live serve clients alone, modifying its journal
# an outage/stop cause live to die
# backup detect that *journal version no longer matching its own local journal
version*: it stop trying to become live
The key parts related to journal age/version are:
* only who's live can change quorum (and local) journal version (with a
monotonic increment)
* every ownership change event must cause journal age/version to change eg
starting as live, loosing its backup, etc etc
Re the RI implementation using Apache Curator, this could use a separate
[DistributedAtomicLong|https://curator.apache.org/apidocs/org/apache/curator/framework/recipes/atomic/DistributedAtomicLong.html]
to manage the journal version.
Although tempting, it's not a good idea to not just use the data field on
{{InterProcessSemaphoreV2}}, because:
* there's no API to query it if no lease is acquired yet (or created)
* we more need to "age" the journal independently from the lock
acquisition/release process eg a live that drop its replica need to increment
the journal version
Athough tempting, it's not a good idea to just use the last alive broker
connector identity instead of a journal version, because of the ABA problem
(see https://en.wikipedia.org/wiki/ABA_problem).
This versioning mechanism isn't without drawbacks: quorum journal versioning
requires to store a local copy of the version in order to allow the broker to
query and compare it with the quorum one on restart; having 2 separate and not
atomic operations means that there must be a way to reconcile/fix it in case of
misalignments. As said above, this could be done with admin operations.
Journal versioning change the way roles behave, but they still retain theirs
key characteristics:
- backup should try start as live in case it has the most up to date journal
and there is no other live around: differently, can just rotate journal and be
available to replicate some live
- primary try to fail-back to any existing live with the most up to date
journal or await it to appear, without becoming live if it doesn't have the
most up-to-date journal
This would ensure that If both broker are up and running and backup allow a
primary to failback, the primary eventually become live and backup replicates
it, preserving the desired broker roles.
> Replicated Journal quorum-based logical timestamp/version
> ---------------------------------------------------------
>
> Key: ARTEMIS-3340
> URL: https://issues.apache.org/jira/browse/ARTEMIS-3340
> Project: ActiveMQ Artemis
> Issue Type: Improvement
> Reporter: Francesco Nigro
> Priority: Major
>
> Shared-nothing replication can cause journal misalignment despite no
> split-brain events.
> There are several ways that can cause this to happen.
> Below some scenario that won't involve network partitions/drastic outages.
> Scenario 1:
> # Master/Primary start as live, clients connect to it
> # Backup become an in-sync replica
> # User stop live and backup failover to it
> # *Backup serve clients alone, modifying its journal*
> # User stop backup
> # User start master/primary: it become live with a journal misaligned to the
> most up-to-date one ie on the stopped backup
> Scenario 2:
> # Master/Primary start as live, clients connect to it
> # Backup become an in-sync replica
> # Connection glitch between backup -> live
> # backup start trying to failover (for {{vote-retries * vote-retry-wait}}
> milliseconds)
> # *Live serve clients alone, modifying its journal*
> # User stop live
> # Backup succeed to failover: it become live with a journal misaligned to
> the most up-to-date one ie on the stopped live
> The main cause of this issue is because we allow *a single broker to serve
> clients*, despite configured with HA, generating the journal misalignment.
> The quorum service (classic or pluggable) just take care of mutual exclusive
> presence of broker for the live role (vs a NodeID), without considering live
> role ordering based on the most up-to-date journal.
> A possible solution is to use
> https://issues.apache.org/jira/browse/ARTEMIS-2716 and use a quorum "logical
> timestamp/version" marking the age/ownership changes of the journal in order
> to force live to always have the most up-to-date journal. It means that such
> value has to be locally saved and exchanged during the initial replica sync,
> involving both journal data and core message protocol changes (just for the
> replication channel, without impacting real clients).
> In case of quorum service restart/outage, admin must use
> command/configuration to let a broker to ignore the age of its journal and
> just force it to start.
> In addition new journal CLI commands should be implemented to inspect the age
> of a (local) broker journal or query/force the quorum journal version too,
> for troubleshooting reasons.
> It's very important to capture every possible event that cause the journal
> age/ownership to change.
> Now let's take a look at Scenario 2 with journal versioning/timestamp:
> # live broker start because it matches the most up to date journal version,
> increasing it (locally and remotely) when it become fully alive
> # backup found it and trust that, given that's live, it already has the
> most-up-to-date journal for a specific NodeID
> # live broker send its journal files to the backup, along with its local
> journal version
> # backup is now ready to failover in any moment: it store the sent journal
> version on its local storage
> # network glitch happen
> # backup try to become live for vote-retries times
> # live detect replication disconnection and *increment the journal version*
> (both quorum and local one)
> # live serve clients alone, modifying its journal
> # outage/stop cause live to die
> # backup detect that *journal version no longer matching its own local
> journal version*: it stop trying to become live
> The key parts related to journal age/version are:
> * only who's live can change quorum (and local) journal version (with a
> monotonic increment)
> * every ownership change event must cause journal age/version to change eg
> starting as live, loosing its backup, etc etc
> Re the RI implementation using Apache Curator, this could use a separate
> [DistributedAtomicLong|https://curator.apache.org/apidocs/org/apache/curator/framework/recipes/atomic/DistributedAtomicLong.html]
> to manage the journal version.
> Although tempting, it's not a good idea to not just use the data field on
> {{InterProcessSemaphoreV2}}, because:
> * there's no API to query it if no lease is acquired yet (or created)
> * we more need to "age" the journal independently from the lock
> acquisition/release process eg a live that drop its replica need to increment
> the journal version
> Athough tempting, it's not a good idea to just use the last alive broker
> connector identity instead of a journal version, because of the ABA problem
> (see https://en.wikipedia.org/wiki/ABA_problem).
> This versioning mechanism isn't without drawbacks: quorum journal versioning
> requires to store a local copy of the version in order to allow the broker to
> query and compare it with the quorum one on restart; having 2 separate and
> not atomic operations means that there must be a way to reconcile/fix it in
> case of misalignments. As said above, this could be done with admin
> operations.
> Journal versioning change the way roles behave, but they still retain theirs
> key characteristics:
> - backup should try start as live in case it has the most up to date journal
> and there is no other live around: differently, can just rotate journal and
> be available to replicate some live
> - primary try to fail-back to any existing live with the most up to date
> journal or await it to appear, without becoming live if it doesn't have the
> most up-to-date journal
> This would ensure that If both broker are up and running and backup allow a
> primary to failback, the primary eventually become live and backup replicates
> it, preserving the desired broker roles.
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