Re: "Idle verify" to "Online verify"

[Alexei Scherbakov]

I've linked to IGNITE-10078 additional related/dependent tickets requiring
investigation as soon as main contribution will be accepted.

вт, 7 мая 2019 г. в 18:10, Alexei Scherbakov :

> Anton,
>
> It's ready for review, look for Patch Available status.
> Yes, atomic caches are not fixed by this contribution. See [1]
>
> [1] https://issues.apache.org/jira/browse/IGNITE-11797
>
> вт, 7 мая 2019 г. в 17:30, Anton Vinogradov :
>
>> Alexei,
>>
>> Got it.
>> Could you please let me know once PR will be ready for review?
>> Currently, have some questions, but, possible, they caused by non-final PR
>> (eg. why atomic counter still ignores misses?).
>>
>> On Tue, May 7, 2019 at 4:43 PM Alexei Scherbakov <
>> alexey.scherbak...@gmail.com> wrote:
>>
>> > Anton,
>> >
>> > 1) Extended counters indeed will answer the question if partition could
>> be
>> > safely restored to synchronized state on all owners.
>> > The only condition - one of owners has no missed updates.
>> > If not, partition must be moved to LOST state, see [1],
>> > TxPartitionCounterStateOnePrimaryTwoBackupsFailAll*Test,
>> >
>> >
>> IgniteSystemProperties#IGNITE_FAIL_NODE_ON_UNRECOVERABLE_PARTITION_INCONSISTENCY
>> > This is known issue and could happen if all partition owners were
>> > unavailable at some point.
>> > In such case we could try to recover consistency using some complex
>> > recovery protocol as you described. Related ticket [2]
>> >
>> > 2) Bitset implementation is considered as an option in GG Community
>> > Edition. No specific implementation dates at the moment.
>> >
>> > 3) As for "online" partition verification,  I think the best option
>> right
>> > now is to do verification partition by partition using read only mode
>> per
>> > group partition under load.
>> > While verification is in progress, all write ops are waiting, not
>> rejected.
>> > This is only 100% reliable way to compare partitions - by touching
>> actual
>> > data, all other ways like pre-computed hash are error prone.
>> > There is already ticket [3] for simplifing grid consistency verification
>> > which could be used as basis for such functionality.
>> > As for avoiding cache pollution, we could try read pages sequentially
>> from
>> > disk without lifting them to pagemem and computing some kind of
>> commutative
>> > hash. It's safe under partition write lock.
>> >
>> > [1] https://issues.apache.org/jira/browse/IGNITE-11611
>> > [2] https://issues.apache.org/jira/browse/IGNITE-6324
>> > [3] https://issues.apache.org/jira/browse/IGNITE-11256
>> >
>> > пн, 6 мая 2019 г. в 16:12, Anton Vinogradov :
>> >
>> > > Ivan,
>> > >
>> > > 1) I've checked the PR [1] and it looks like it does not solve the
>> issue
>> > > too.
>> > > AFAICS, the main goal here (at PR) is to produce
>> > > PartitionUpdateCounter#sequential which can be false for all backups,
>> > what
>> > > backup should win in that case?
>> > >
>> > > Is there any IEP or some another design page for this fix?
>> > >
>> > > Looks like extended counters should be able to recover the whole
>> cluster
>> > > even in case all copies of the same partition are broken.
>> > > So, seems, the counter should provide detailed info:
>> > > - biggest applied updateCounter
>> > > - list of all missed counters before biggest applied
>> > > - optional hash
>> > >
>> > > In that case, we'll be able to perform some exchange between broken
>> > copies.
>> > > For example, we'll found that copy1 missed key1, and copy2 missed
>> key2.
>> > > It's pretty simple to fix both copies in that case.
>> > > In case all misses can be solved this way, we'll continue cluster
>> > > activation like it was not broken before.
>> > >
>> > > 2) Seems I see the simpler solution to handle misses (than at PR).
>> > > Once you have newUpdateCounter > curUpdateCounter + 1, you should add
>> > byte
>> > > (or int or long (smaplest possible)) value to special structure.
>> > > This value will represent delta between newUpdateCounter and
>> > > curUpdateCounter in bitmask way.
>> > > In case you'll handle updateCounter less that curUpdateCounter, you
>> > should
>> > > update the value at structure responsible to this delta.
>> > > For example, when you have delta "2 to 6", you will have 
>> > initially
>> > > and 0001 finally.
>> > > Each delta update should be finished with check it completed (value
>> == 31
>> > > in this case). Once it finished, it should be removed from the
>> structure.
>> > > Deltas can and should be reused to solve GC issue.
>> > >
>> > > What do you think about the proposed solution?
>> > >
>> > > 3) Hash computation can be an additional extension for extended
>> counters,
>> > > just one more dimension to be extremely sure everything is ok.
>> > > Any objections?
>> > >
>> > > [1] https://github.com/apache/ignite/pull/5765
>> > >
>> > > On Mon, May 6, 2019 at 12:48 PM Ivan Rakov 
>> > wrote:
>> > >
>> > > > Anton,
>> > > >
>> > > > Automatic quorum-based partition drop may work as a partial
>> workaround
>> > >

Re: "Idle verify" to "Online verify"

[Alexei Scherbakov]

Anton,

It's ready for review, look for Patch Available status.
Yes, atomic caches are not fixed by this contribution. See [1]

[1] https://issues.apache.org/jira/browse/IGNITE-11797

вт, 7 мая 2019 г. в 17:30, Anton Vinogradov :

> Alexei,
>
> Got it.
> Could you please let me know once PR will be ready for review?
> Currently, have some questions, but, possible, they caused by non-final PR
> (eg. why atomic counter still ignores misses?).
>
> On Tue, May 7, 2019 at 4:43 PM Alexei Scherbakov <
> alexey.scherbak...@gmail.com> wrote:
>
> > Anton,
> >
> > 1) Extended counters indeed will answer the question if partition could
> be
> > safely restored to synchronized state on all owners.
> > The only condition - one of owners has no missed updates.
> > If not, partition must be moved to LOST state, see [1],
> > TxPartitionCounterStateOnePrimaryTwoBackupsFailAll*Test,
> >
> >
> IgniteSystemProperties#IGNITE_FAIL_NODE_ON_UNRECOVERABLE_PARTITION_INCONSISTENCY
> > This is known issue and could happen if all partition owners were
> > unavailable at some point.
> > In such case we could try to recover consistency using some complex
> > recovery protocol as you described. Related ticket [2]
> >
> > 2) Bitset implementation is considered as an option in GG Community
> > Edition. No specific implementation dates at the moment.
> >
> > 3) As for "online" partition verification,  I think the best option right
> > now is to do verification partition by partition using read only mode per
> > group partition under load.
> > While verification is in progress, all write ops are waiting, not
> rejected.
> > This is only 100% reliable way to compare partitions - by touching actual
> > data, all other ways like pre-computed hash are error prone.
> > There is already ticket [3] for simplifing grid consistency verification
> > which could be used as basis for such functionality.
> > As for avoiding cache pollution, we could try read pages sequentially
> from
> > disk without lifting them to pagemem and computing some kind of
> commutative
> > hash. It's safe under partition write lock.
> >
> > [1] https://issues.apache.org/jira/browse/IGNITE-11611
> > [2] https://issues.apache.org/jira/browse/IGNITE-6324
> > [3] https://issues.apache.org/jira/browse/IGNITE-11256
> >
> > пн, 6 мая 2019 г. в 16:12, Anton Vinogradov :
> >
> > > Ivan,
> > >
> > > 1) I've checked the PR [1] and it looks like it does not solve the
> issue
> > > too.
> > > AFAICS, the main goal here (at PR) is to produce
> > > PartitionUpdateCounter#sequential which can be false for all backups,
> > what
> > > backup should win in that case?
> > >
> > > Is there any IEP or some another design page for this fix?
> > >
> > > Looks like extended counters should be able to recover the whole
> cluster
> > > even in case all copies of the same partition are broken.
> > > So, seems, the counter should provide detailed info:
> > > - biggest applied updateCounter
> > > - list of all missed counters before biggest applied
> > > - optional hash
> > >
> > > In that case, we'll be able to perform some exchange between broken
> > copies.
> > > For example, we'll found that copy1 missed key1, and copy2 missed key2.
> > > It's pretty simple to fix both copies in that case.
> > > In case all misses can be solved this way, we'll continue cluster
> > > activation like it was not broken before.
> > >
> > > 2) Seems I see the simpler solution to handle misses (than at PR).
> > > Once you have newUpdateCounter > curUpdateCounter + 1, you should add
> > byte
> > > (or int or long (smaplest possible)) value to special structure.
> > > This value will represent delta between newUpdateCounter and
> > > curUpdateCounter in bitmask way.
> > > In case you'll handle updateCounter less that curUpdateCounter, you
> > should
> > > update the value at structure responsible to this delta.
> > > For example, when you have delta "2 to 6", you will have 
> > initially
> > > and 0001 finally.
> > > Each delta update should be finished with check it completed (value ==
> 31
> > > in this case). Once it finished, it should be removed from the
> structure.
> > > Deltas can and should be reused to solve GC issue.
> > >
> > > What do you think about the proposed solution?
> > >
> > > 3) Hash computation can be an additional extension for extended
> counters,
> > > just one more dimension to be extremely sure everything is ok.
> > > Any objections?
> > >
> > > [1] https://github.com/apache/ignite/pull/5765
> > >
> > > On Mon, May 6, 2019 at 12:48 PM Ivan Rakov 
> > wrote:
> > >
> > > > Anton,
> > > >
> > > > Automatic quorum-based partition drop may work as a partial
> workaround
> > > > for IGNITE-10078, but discussed approach surely doesn't replace
> > > > IGNITE-10078 activity. We still don't know what do to when quorum
> can't
> > > > be reached (2 partitions have hash X, 2 have hash Y) and keeping
> > > > extended update counters is the only way to resolve such case.
> > > > On the other hand, pre

Re: "Idle verify" to "Online verify"

[Anton Vinogradov]

Alexei,

Got it.
Could you please let me know once PR will be ready for review?
Currently, have some questions, but, possible, they caused by non-final PR
(eg. why atomic counter still ignores misses?).

On Tue, May 7, 2019 at 4:43 PM Alexei Scherbakov <
alexey.scherbak...@gmail.com> wrote:

> Anton,
>
> 1) Extended counters indeed will answer the question if partition could be
> safely restored to synchronized state on all owners.
> The only condition - one of owners has no missed updates.
> If not, partition must be moved to LOST state, see [1],
> TxPartitionCounterStateOnePrimaryTwoBackupsFailAll*Test,
>
> IgniteSystemProperties#IGNITE_FAIL_NODE_ON_UNRECOVERABLE_PARTITION_INCONSISTENCY
> This is known issue and could happen if all partition owners were
> unavailable at some point.
> In such case we could try to recover consistency using some complex
> recovery protocol as you described. Related ticket [2]
>
> 2) Bitset implementation is considered as an option in GG Community
> Edition. No specific implementation dates at the moment.
>
> 3) As for "online" partition verification,  I think the best option right
> now is to do verification partition by partition using read only mode per
> group partition under load.
> While verification is in progress, all write ops are waiting, not rejected.
> This is only 100% reliable way to compare partitions - by touching actual
> data, all other ways like pre-computed hash are error prone.
> There is already ticket [3] for simplifing grid consistency verification
> which could be used as basis for such functionality.
> As for avoiding cache pollution, we could try read pages sequentially from
> disk without lifting them to pagemem and computing some kind of commutative
> hash. It's safe under partition write lock.
>
> [1] https://issues.apache.org/jira/browse/IGNITE-11611
> [2] https://issues.apache.org/jira/browse/IGNITE-6324
> [3] https://issues.apache.org/jira/browse/IGNITE-11256
>
> пн, 6 мая 2019 г. в 16:12, Anton Vinogradov :
>
> > Ivan,
> >
> > 1) I've checked the PR [1] and it looks like it does not solve the issue
> > too.
> > AFAICS, the main goal here (at PR) is to produce
> > PartitionUpdateCounter#sequential which can be false for all backups,
> what
> > backup should win in that case?
> >
> > Is there any IEP or some another design page for this fix?
> >
> > Looks like extended counters should be able to recover the whole cluster
> > even in case all copies of the same partition are broken.
> > So, seems, the counter should provide detailed info:
> > - biggest applied updateCounter
> > - list of all missed counters before biggest applied
> > - optional hash
> >
> > In that case, we'll be able to perform some exchange between broken
> copies.
> > For example, we'll found that copy1 missed key1, and copy2 missed key2.
> > It's pretty simple to fix both copies in that case.
> > In case all misses can be solved this way, we'll continue cluster
> > activation like it was not broken before.
> >
> > 2) Seems I see the simpler solution to handle misses (than at PR).
> > Once you have newUpdateCounter > curUpdateCounter + 1, you should add
> byte
> > (or int or long (smaplest possible)) value to special structure.
> > This value will represent delta between newUpdateCounter and
> > curUpdateCounter in bitmask way.
> > In case you'll handle updateCounter less that curUpdateCounter, you
> should
> > update the value at structure responsible to this delta.
> > For example, when you have delta "2 to 6", you will have 
> initially
> > and 0001 finally.
> > Each delta update should be finished with check it completed (value == 31
> > in this case). Once it finished, it should be removed from the structure.
> > Deltas can and should be reused to solve GC issue.
> >
> > What do you think about the proposed solution?
> >
> > 3) Hash computation can be an additional extension for extended counters,
> > just one more dimension to be extremely sure everything is ok.
> > Any objections?
> >
> > [1] https://github.com/apache/ignite/pull/5765
> >
> > On Mon, May 6, 2019 at 12:48 PM Ivan Rakov 
> wrote:
> >
> > > Anton,
> > >
> > > Automatic quorum-based partition drop may work as a partial workaround
> > > for IGNITE-10078, but discussed approach surely doesn't replace
> > > IGNITE-10078 activity. We still don't know what do to when quorum can't
> > > be reached (2 partitions have hash X, 2 have hash Y) and keeping
> > > extended update counters is the only way to resolve such case.
> > > On the other hand, precalculated partition hashes validation on PME can
> > > be a good addition to IGNITE-10078 logic: we'll be able to detect
> > > situations when extended update counters are equal, but for some reason
> > > (bug or whatsoever) partition contents are different.
> > >
> > > Best Regards,
> > > Ivan Rakov
> > >
> > > On 06.05.2019 12:27, Anton Vinogradov wrote:
> > > > Ivan, just to make sure ...
> > > > The discussed case will fully solve the issue [1] in case 

Re: "Idle verify" to "Online verify"

[Alexei Scherbakov]

Anton,

1) Extended counters indeed will answer the question if partition could be
safely restored to synchronized state on all owners.
The only condition - one of owners has no missed updates.
If not, partition must be moved to LOST state, see [1],
TxPartitionCounterStateOnePrimaryTwoBackupsFailAll*Test,
IgniteSystemProperties#IGNITE_FAIL_NODE_ON_UNRECOVERABLE_PARTITION_INCONSISTENCY
This is known issue and could happen if all partition owners were
unavailable at some point.
In such case we could try to recover consistency using some complex
recovery protocol as you described. Related ticket [2]

2) Bitset implementation is considered as an option in GG Community
Edition. No specific implementation dates at the moment.

3) As for "online" partition verification,  I think the best option right
now is to do verification partition by partition using read only mode per
group partition under load.
While verification is in progress, all write ops are waiting, not rejected.
This is only 100% reliable way to compare partitions - by touching actual
data, all other ways like pre-computed hash are error prone.
There is already ticket [3] for simplifing grid consistency verification
which could be used as basis for such functionality.
As for avoiding cache pollution, we could try read pages sequentially from
disk without lifting them to pagemem and computing some kind of commutative
hash. It's safe under partition write lock.

[1] https://issues.apache.org/jira/browse/IGNITE-11611
[2] https://issues.apache.org/jira/browse/IGNITE-6324
[3] https://issues.apache.org/jira/browse/IGNITE-11256

пн, 6 мая 2019 г. в 16:12, Anton Vinogradov :

> Ivan,
>
> 1) I've checked the PR [1] and it looks like it does not solve the issue
> too.
> AFAICS, the main goal here (at PR) is to produce
> PartitionUpdateCounter#sequential which can be false for all backups, what
> backup should win in that case?
>
> Is there any IEP or some another design page for this fix?
>
> Looks like extended counters should be able to recover the whole cluster
> even in case all copies of the same partition are broken.
> So, seems, the counter should provide detailed info:
> - biggest applied updateCounter
> - list of all missed counters before biggest applied
> - optional hash
>
> In that case, we'll be able to perform some exchange between broken copies.
> For example, we'll found that copy1 missed key1, and copy2 missed key2.
> It's pretty simple to fix both copies in that case.
> In case all misses can be solved this way, we'll continue cluster
> activation like it was not broken before.
>
> 2) Seems I see the simpler solution to handle misses (than at PR).
> Once you have newUpdateCounter > curUpdateCounter + 1, you should add byte
> (or int or long (smaplest possible)) value to special structure.
> This value will represent delta between newUpdateCounter and
> curUpdateCounter in bitmask way.
> In case you'll handle updateCounter less that curUpdateCounter, you should
> update the value at structure responsible to this delta.
> For example, when you have delta "2 to 6", you will have  initially
> and 0001 finally.
> Each delta update should be finished with check it completed (value == 31
> in this case). Once it finished, it should be removed from the structure.
> Deltas can and should be reused to solve GC issue.
>
> What do you think about the proposed solution?
>
> 3) Hash computation can be an additional extension for extended counters,
> just one more dimension to be extremely sure everything is ok.
> Any objections?
>
> [1] https://github.com/apache/ignite/pull/5765
>
> On Mon, May 6, 2019 at 12:48 PM Ivan Rakov  wrote:
>
> > Anton,
> >
> > Automatic quorum-based partition drop may work as a partial workaround
> > for IGNITE-10078, but discussed approach surely doesn't replace
> > IGNITE-10078 activity. We still don't know what do to when quorum can't
> > be reached (2 partitions have hash X, 2 have hash Y) and keeping
> > extended update counters is the only way to resolve such case.
> > On the other hand, precalculated partition hashes validation on PME can
> > be a good addition to IGNITE-10078 logic: we'll be able to detect
> > situations when extended update counters are equal, but for some reason
> > (bug or whatsoever) partition contents are different.
> >
> > Best Regards,
> > Ivan Rakov
> >
> > On 06.05.2019 12:27, Anton Vinogradov wrote:
> > > Ivan, just to make sure ...
> > > The discussed case will fully solve the issue [1] in case we'll also
> add
> > > some strategy to reject partitions with missed updates (updateCnt==Ok,
> > > Hash!=Ok).
> > > For example, we may use the Quorum strategy, when the majority wins.
> > > Sounds correct?
> > >
> > > [1] https://issues.apache.org/jira/browse/IGNITE-10078
> > >
> > > On Tue, Apr 30, 2019 at 3:14 PM Anton Vinogradov 
> wrote:
> > >
> > >> Ivan,
> > >>
> > >> Thanks for the detailed explanation.
> > >> I'll try to implement the PoC to check the idea.
> > >>
> > >> On Mon, Apr

Re: "Idle verify" to "Online verify"

[Anton Vinogradov]

Ivan,

1) I've checked the PR [1] and it looks like it does not solve the issue
too.
AFAICS, the main goal here (at PR) is to produce
PartitionUpdateCounter#sequential which can be false for all backups, what
backup should win in that case?

Is there any IEP or some another design page for this fix?

Looks like extended counters should be able to recover the whole cluster
even in case all copies of the same partition are broken.
So, seems, the counter should provide detailed info:
- biggest applied updateCounter
- list of all missed counters before biggest applied
- optional hash

In that case, we'll be able to perform some exchange between broken copies.
For example, we'll found that copy1 missed key1, and copy2 missed key2.
It's pretty simple to fix both copies in that case.
In case all misses can be solved this way, we'll continue cluster
activation like it was not broken before.

2) Seems I see the simpler solution to handle misses (than at PR).
Once you have newUpdateCounter > curUpdateCounter + 1, you should add byte
(or int or long (smaplest possible)) value to special structure.
This value will represent delta between newUpdateCounter and
curUpdateCounter in bitmask way.
In case you'll handle updateCounter less that curUpdateCounter, you should
update the value at structure responsible to this delta.
For example, when you have delta "2 to 6", you will have  initially
and 0001 finally.
Each delta update should be finished with check it completed (value == 31
in this case). Once it finished, it should be removed from the structure.
Deltas can and should be reused to solve GC issue.

What do you think about the proposed solution?

3) Hash computation can be an additional extension for extended counters,
just one more dimension to be extremely sure everything is ok.
Any objections?

[1] https://github.com/apache/ignite/pull/5765

On Mon, May 6, 2019 at 12:48 PM Ivan Rakov  wrote:

> Anton,
>
> Automatic quorum-based partition drop may work as a partial workaround
> for IGNITE-10078, but discussed approach surely doesn't replace
> IGNITE-10078 activity. We still don't know what do to when quorum can't
> be reached (2 partitions have hash X, 2 have hash Y) and keeping
> extended update counters is the only way to resolve such case.
> On the other hand, precalculated partition hashes validation on PME can
> be a good addition to IGNITE-10078 logic: we'll be able to detect
> situations when extended update counters are equal, but for some reason
> (bug or whatsoever) partition contents are different.
>
> Best Regards,
> Ivan Rakov
>
> On 06.05.2019 12:27, Anton Vinogradov wrote:
> > Ivan, just to make sure ...
> > The discussed case will fully solve the issue [1] in case we'll also add
> > some strategy to reject partitions with missed updates (updateCnt==Ok,
> > Hash!=Ok).
> > For example, we may use the Quorum strategy, when the majority wins.
> > Sounds correct?
> >
> > [1] https://issues.apache.org/jira/browse/IGNITE-10078
> >
> > On Tue, Apr 30, 2019 at 3:14 PM Anton Vinogradov  wrote:
> >
> >> Ivan,
> >>
> >> Thanks for the detailed explanation.
> >> I'll try to implement the PoC to check the idea.
> >>
> >> On Mon, Apr 29, 2019 at 8:22 PM Ivan Rakov 
> wrote:
> >>
>  But how to keep this hash?
> >>> I think, we can just adopt way of storing partition update counters.
> >>> Update counters are:
> >>> 1) Kept and updated in heap, see
> >>> IgniteCacheOffheapManagerImpl.CacheDataStoreImpl#pCntr (accessed during
> >>> regular cache operations, no page replacement latency issues)
> >>> 2) Synchronized with page memory (and with disk) on every checkpoint,
> >>> see GridCacheOffheapManager#saveStoreMetadata
> >>> 3) Stored in partition meta page, see
> PagePartitionMetaIO#setUpdateCounter
> >>> 4) On node restart, we init onheap counter with value from disk (for
> the
> >>> moment of last checkpoint) and update it to latest value during WAL
> >>> logical records replay
> >>>
>  2) PME is a rare operation on production cluster, but, seems, we have
>  to check consistency in a regular way.
>  Since we have to finish all operations before the check, should we
>  have fake PME for maintenance check in this case?
> >>>   From my experience, PME happens on prod clusters from time to time
> >>> (several times per week), which can be enough. In case it's needed to
> >>> check consistency more often than regular PMEs occur, we can implement
> >>> command that will trigger fake PME for consistency checking.
> >>>
> >>> Best Regards,
> >>> Ivan Rakov
> >>>
> >>> On 29.04.2019 18:53, Anton Vinogradov wrote:
>  Ivan, thanks for the analysis!
> 
> >> With having pre-calculated partition hash value, we can
>  automatically detect inconsistent partitions on every PME.
>  Great idea, seems this covers all broken synс cases.
> 
>  It will check alive nodes in case the primary failed immediately
>  and will check rejoining node once it finished a rebalance (PME 

Re: "Idle verify" to "Online verify"

[Ivan Rakov]

Anton,

Automatic quorum-based partition drop may work as a partial workaround 
for IGNITE-10078, but discussed approach surely doesn't replace 
IGNITE-10078 activity. We still don't know what do to when quorum can't 
be reached (2 partitions have hash X, 2 have hash Y) and keeping 
extended update counters is the only way to resolve such case.
On the other hand, precalculated partition hashes validation on PME can 
be a good addition to IGNITE-10078 logic: we'll be able to detect 
situations when extended update counters are equal, but for some reason 
(bug or whatsoever) partition contents are different.


Best Regards,
Ivan Rakov

On 06.05.2019 12:27, Anton Vinogradov wrote:

Ivan, just to make sure ...
The discussed case will fully solve the issue [1] in case we'll also add
some strategy to reject partitions with missed updates (updateCnt==Ok,
Hash!=Ok).
For example, we may use the Quorum strategy, when the majority wins.
Sounds correct?

[1] https://issues.apache.org/jira/browse/IGNITE-10078

On Tue, Apr 30, 2019 at 3:14 PM Anton Vinogradov  wrote:


Ivan,

Thanks for the detailed explanation.
I'll try to implement the PoC to check the idea.

On Mon, Apr 29, 2019 at 8:22 PM Ivan Rakov  wrote:


But how to keep this hash?

I think, we can just adopt way of storing partition update counters.
Update counters are:
1) Kept and updated in heap, see
IgniteCacheOffheapManagerImpl.CacheDataStoreImpl#pCntr (accessed during
regular cache operations, no page replacement latency issues)
2) Synchronized with page memory (and with disk) on every checkpoint,
see GridCacheOffheapManager#saveStoreMetadata
3) Stored in partition meta page, see PagePartitionMetaIO#setUpdateCounter
4) On node restart, we init onheap counter with value from disk (for the
moment of last checkpoint) and update it to latest value during WAL
logical records replay


2) PME is a rare operation on production cluster, but, seems, we have
to check consistency in a regular way.
Since we have to finish all operations before the check, should we
have fake PME for maintenance check in this case?

  From my experience, PME happens on prod clusters from time to time
(several times per week), which can be enough. In case it's needed to
check consistency more often than regular PMEs occur, we can implement
command that will trigger fake PME for consistency checking.

Best Regards,
Ivan Rakov

On 29.04.2019 18:53, Anton Vinogradov wrote:

Ivan, thanks for the analysis!


With having pre-calculated partition hash value, we can

automatically detect inconsistent partitions on every PME.
Great idea, seems this covers all broken synс cases.

It will check alive nodes in case the primary failed immediately
and will check rejoining node once it finished a rebalance (PME on
becoming an owner).
Recovered cluster will be checked on activation PME (or even before
that?).
Also, warmed cluster will be still warmed after check.

Have I missed some cases leads to broken sync except bugs?

1) But how to keep this hash?
- It should be automatically persisted on each checkpoint (it should
not require recalculation on restore, snapshots should be covered too)
(and covered by WAL?).
- It should be always available at RAM for every partition (even for
cold partitions never updated/readed on this node) to be immediately
used once all operations done on PME.

Can we have special pages to keep such hashes and never allow their
eviction?

2) PME is a rare operation on production cluster, but, seems, we have
to check consistency in a regular way.
Since we have to finish all operations before the check, should we
have fake PME for maintenance check in this case?

On Mon, Apr 29, 2019 at 4:59 PM Ivan Rakov mailto:ivan.glu...@gmail.com>> wrote:

 Hi Anton,

 Thanks for sharing your ideas.
 I think your approach should work in general. I'll just share my
 concerns about possible issues that may come up.

 1) Equality of update counters doesn't imply equality of
 partitions content under load.
 For every update, primary node generates update counter and then
 update is delivered to backup node and gets applied with the
 corresponding update counter. For example, there are two
 transactions (A and B) that update partition X by the following
 scenario:
 - A updates key1 in partition X on primary node and increments
 counter to 10
 - B updates key2 in partition X on primary node and increments
 counter to 11
 - While A is still updating another keys, B is finally committed
 - Update of key2 arrives to backup node and sets update counter to

11

 Observer will see equal update counters (11), but update of key 1
 is still missing in the backup partition.
 This is a fundamental problem which is being solved here:
 https://issues.apache.org/jira/browse/IGNITE-10078
 "Online verify" should operate with new complex update counters
 which take such "update holes" into account. Otherwise, online
 veri

Re: "Idle verify" to "Online verify"

[Anton Vinogradov]

Ivan, just to make sure ...
The discussed case will fully solve the issue [1] in case we'll also add
some strategy to reject partitions with missed updates (updateCnt==Ok,
Hash!=Ok).
For example, we may use the Quorum strategy, when the majority wins.
Sounds correct?

[1] https://issues.apache.org/jira/browse/IGNITE-10078

On Tue, Apr 30, 2019 at 3:14 PM Anton Vinogradov  wrote:

> Ivan,
>
> Thanks for the detailed explanation.
> I'll try to implement the PoC to check the idea.
>
> On Mon, Apr 29, 2019 at 8:22 PM Ivan Rakov  wrote:
>
>> > But how to keep this hash?
>> I think, we can just adopt way of storing partition update counters.
>> Update counters are:
>> 1) Kept and updated in heap, see
>> IgniteCacheOffheapManagerImpl.CacheDataStoreImpl#pCntr (accessed during
>> regular cache operations, no page replacement latency issues)
>> 2) Synchronized with page memory (and with disk) on every checkpoint,
>> see GridCacheOffheapManager#saveStoreMetadata
>> 3) Stored in partition meta page, see PagePartitionMetaIO#setUpdateCounter
>> 4) On node restart, we init onheap counter with value from disk (for the
>> moment of last checkpoint) and update it to latest value during WAL
>> logical records replay
>>
>> > 2) PME is a rare operation on production cluster, but, seems, we have
>> > to check consistency in a regular way.
>> > Since we have to finish all operations before the check, should we
>> > have fake PME for maintenance check in this case?
>>  From my experience, PME happens on prod clusters from time to time
>> (several times per week), which can be enough. In case it's needed to
>> check consistency more often than regular PMEs occur, we can implement
>> command that will trigger fake PME for consistency checking.
>>
>> Best Regards,
>> Ivan Rakov
>>
>> On 29.04.2019 18:53, Anton Vinogradov wrote:
>> > Ivan, thanks for the analysis!
>> >
>> > >> With having pre-calculated partition hash value, we can
>> > automatically detect inconsistent partitions on every PME.
>> > Great idea, seems this covers all broken synс cases.
>> >
>> > It will check alive nodes in case the primary failed immediately
>> > and will check rejoining node once it finished a rebalance (PME on
>> > becoming an owner).
>> > Recovered cluster will be checked on activation PME (or even before
>> > that?).
>> > Also, warmed cluster will be still warmed after check.
>> >
>> > Have I missed some cases leads to broken sync except bugs?
>> >
>> > 1) But how to keep this hash?
>> > - It should be automatically persisted on each checkpoint (it should
>> > not require recalculation on restore, snapshots should be covered too)
>> > (and covered by WAL?).
>> > - It should be always available at RAM for every partition (even for
>> > cold partitions never updated/readed on this node) to be immediately
>> > used once all operations done on PME.
>> >
>> > Can we have special pages to keep such hashes and never allow their
>> > eviction?
>> >
>> > 2) PME is a rare operation on production cluster, but, seems, we have
>> > to check consistency in a regular way.
>> > Since we have to finish all operations before the check, should we
>> > have fake PME for maintenance check in this case?
>> >
>> > On Mon, Apr 29, 2019 at 4:59 PM Ivan Rakov > > > wrote:
>> >
>> > Hi Anton,
>> >
>> > Thanks for sharing your ideas.
>> > I think your approach should work in general. I'll just share my
>> > concerns about possible issues that may come up.
>> >
>> > 1) Equality of update counters doesn't imply equality of
>> > partitions content under load.
>> > For every update, primary node generates update counter and then
>> > update is delivered to backup node and gets applied with the
>> > corresponding update counter. For example, there are two
>> > transactions (A and B) that update partition X by the following
>> > scenario:
>> > - A updates key1 in partition X on primary node and increments
>> > counter to 10
>> > - B updates key2 in partition X on primary node and increments
>> > counter to 11
>> > - While A is still updating another keys, B is finally committed
>> > - Update of key2 arrives to backup node and sets update counter to
>> 11
>> > Observer will see equal update counters (11), but update of key 1
>> > is still missing in the backup partition.
>> > This is a fundamental problem which is being solved here:
>> > https://issues.apache.org/jira/browse/IGNITE-10078
>> > "Online verify" should operate with new complex update counters
>> > which take such "update holes" into account. Otherwise, online
>> > verify may provide false-positive inconsistency reports.
>> >
>> > 2) Acquisition and comparison of update counters is fast, but
>> > partition hash calculation is long. We should check that update
>> > counter remains unchanged after every K keys handled.
>> >
>> > 3)
>> >
>> >> Another hope is that we'll be able 

Re: "Idle verify" to "Online verify"

[Anton Vinogradov]

Ivan,

Thanks for the detailed explanation.
I'll try to implement the PoC to check the idea.

On Mon, Apr 29, 2019 at 8:22 PM Ivan Rakov  wrote:

> > But how to keep this hash?
> I think, we can just adopt way of storing partition update counters.
> Update counters are:
> 1) Kept and updated in heap, see
> IgniteCacheOffheapManagerImpl.CacheDataStoreImpl#pCntr (accessed during
> regular cache operations, no page replacement latency issues)
> 2) Synchronized with page memory (and with disk) on every checkpoint,
> see GridCacheOffheapManager#saveStoreMetadata
> 3) Stored in partition meta page, see PagePartitionMetaIO#setUpdateCounter
> 4) On node restart, we init onheap counter with value from disk (for the
> moment of last checkpoint) and update it to latest value during WAL
> logical records replay
>
> > 2) PME is a rare operation on production cluster, but, seems, we have
> > to check consistency in a regular way.
> > Since we have to finish all operations before the check, should we
> > have fake PME for maintenance check in this case?
>  From my experience, PME happens on prod clusters from time to time
> (several times per week), which can be enough. In case it's needed to
> check consistency more often than regular PMEs occur, we can implement
> command that will trigger fake PME for consistency checking.
>
> Best Regards,
> Ivan Rakov
>
> On 29.04.2019 18:53, Anton Vinogradov wrote:
> > Ivan, thanks for the analysis!
> >
> > >> With having pre-calculated partition hash value, we can
> > automatically detect inconsistent partitions on every PME.
> > Great idea, seems this covers all broken synс cases.
> >
> > It will check alive nodes in case the primary failed immediately
> > and will check rejoining node once it finished a rebalance (PME on
> > becoming an owner).
> > Recovered cluster will be checked on activation PME (or even before
> > that?).
> > Also, warmed cluster will be still warmed after check.
> >
> > Have I missed some cases leads to broken sync except bugs?
> >
> > 1) But how to keep this hash?
> > - It should be automatically persisted on each checkpoint (it should
> > not require recalculation on restore, snapshots should be covered too)
> > (and covered by WAL?).
> > - It should be always available at RAM for every partition (even for
> > cold partitions never updated/readed on this node) to be immediately
> > used once all operations done on PME.
> >
> > Can we have special pages to keep such hashes and never allow their
> > eviction?
> >
> > 2) PME is a rare operation on production cluster, but, seems, we have
> > to check consistency in a regular way.
> > Since we have to finish all operations before the check, should we
> > have fake PME for maintenance check in this case?
> >
> > On Mon, Apr 29, 2019 at 4:59 PM Ivan Rakov  > > wrote:
> >
> > Hi Anton,
> >
> > Thanks for sharing your ideas.
> > I think your approach should work in general. I'll just share my
> > concerns about possible issues that may come up.
> >
> > 1) Equality of update counters doesn't imply equality of
> > partitions content under load.
> > For every update, primary node generates update counter and then
> > update is delivered to backup node and gets applied with the
> > corresponding update counter. For example, there are two
> > transactions (A and B) that update partition X by the following
> > scenario:
> > - A updates key1 in partition X on primary node and increments
> > counter to 10
> > - B updates key2 in partition X on primary node and increments
> > counter to 11
> > - While A is still updating another keys, B is finally committed
> > - Update of key2 arrives to backup node and sets update counter to 11
> > Observer will see equal update counters (11), but update of key 1
> > is still missing in the backup partition.
> > This is a fundamental problem which is being solved here:
> > https://issues.apache.org/jira/browse/IGNITE-10078
> > "Online verify" should operate with new complex update counters
> > which take such "update holes" into account. Otherwise, online
> > verify may provide false-positive inconsistency reports.
> >
> > 2) Acquisition and comparison of update counters is fast, but
> > partition hash calculation is long. We should check that update
> > counter remains unchanged after every K keys handled.
> >
> > 3)
> >
> >> Another hope is that we'll be able to pause/continue scan, for
> >> example, we'll check 1/3 partitions today, 1/3 tomorrow, and in
> >> three days we'll check the whole cluster.
> > Totally makes sense.
> > We may find ourselves into a situation where some "hot" partitions
> > are still unprocessed, and every next attempt to calculate
> > partition hash fails due to another concurrent update. We should
> > be able to track progress of validation (% of calculation time
> > wasted due to co

Re: "Idle verify" to "Online verify"

[Ivan Rakov]

But how to keep this hash?

I think, we can just adopt way of storing partition update counters.
Update counters are:
1) Kept and updated in heap, see 
IgniteCacheOffheapManagerImpl.CacheDataStoreImpl#pCntr (accessed during 
regular cache operations, no page replacement latency issues)
2) Synchronized with page memory (and with disk) on every checkpoint, 
see GridCacheOffheapManager#saveStoreMetadata

3) Stored in partition meta page, see PagePartitionMetaIO#setUpdateCounter
4) On node restart, we init onheap counter with value from disk (for the 
moment of last checkpoint) and update it to latest value during WAL 
logical records replay


2) PME is a rare operation on production cluster, but, seems, we have 
to check consistency in a regular way.
Since we have to finish all operations before the check, should we 
have fake PME for maintenance check in this case?
From my experience, PME happens on prod clusters from time to time 
(several times per week), which can be enough. In case it's needed to 
check consistency more often than regular PMEs occur, we can implement 
command that will trigger fake PME for consistency checking.


Best Regards,
Ivan Rakov

On 29.04.2019 18:53, Anton Vinogradov wrote:

Ivan, thanks for the analysis!

>> With having pre-calculated partition hash value, we can 
automatically detect inconsistent partitions on every PME.

Great idea, seems this covers all broken synс cases.

It will check alive nodes in case the primary failed immediately
and will check rejoining node once it finished a rebalance (PME on 
becoming an owner).
Recovered cluster will be checked on activation PME (or even before 
that?).

Also, warmed cluster will be still warmed after check.

Have I missed some cases leads to broken sync except bugs?

1) But how to keep this hash?
- It should be automatically persisted on each checkpoint (it should 
not require recalculation on restore, snapshots should be covered too) 
(and covered by WAL?).
- It should be always available at RAM for every partition (even for 
cold partitions never updated/readed on this node) to be immediately 
used once all operations done on PME.


Can we have special pages to keep such hashes and never allow their 
eviction?


2) PME is a rare operation on production cluster, but, seems, we have 
to check consistency in a regular way.
Since we have to finish all operations before the check, should we 
have fake PME for maintenance check in this case?


On Mon, Apr 29, 2019 at 4:59 PM Ivan Rakov > wrote:


Hi Anton,

Thanks for sharing your ideas.
I think your approach should work in general. I'll just share my
concerns about possible issues that may come up.

1) Equality of update counters doesn't imply equality of
partitions content under load.
For every update, primary node generates update counter and then
update is delivered to backup node and gets applied with the
corresponding update counter. For example, there are two
transactions (A and B) that update partition X by the following
scenario:
- A updates key1 in partition X on primary node and increments
counter to 10
- B updates key2 in partition X on primary node and increments
counter to 11
- While A is still updating another keys, B is finally committed
- Update of key2 arrives to backup node and sets update counter to 11
Observer will see equal update counters (11), but update of key 1
is still missing in the backup partition.
This is a fundamental problem which is being solved here:
https://issues.apache.org/jira/browse/IGNITE-10078
"Online verify" should operate with new complex update counters
which take such "update holes" into account. Otherwise, online
verify may provide false-positive inconsistency reports.

2) Acquisition and comparison of update counters is fast, but
partition hash calculation is long. We should check that update
counter remains unchanged after every K keys handled.

3)


Another hope is that we'll be able to pause/continue scan, for
example, we'll check 1/3 partitions today, 1/3 tomorrow, and in
three days we'll check the whole cluster.

Totally makes sense.
We may find ourselves into a situation where some "hot" partitions
are still unprocessed, and every next attempt to calculate
partition hash fails due to another concurrent update. We should
be able to track progress of validation (% of calculation time
wasted due to concurrent operations may be a good metric, 100% is
the worst case) and provide option to stop/pause activity.
I think, pause should return an "intermediate results report" with
information about which partitions have been successfully checked.
With such report, we can resume activity later: partitions from
report will be just skipped.

4)


Since "Idle verify" uses regular pagmem, I assume it replaces hot
data with persisted.

Re: "Idle verify" to "Online verify"

[Anton Vinogradov]

Ivan, thanks for the analysis!

>> With having pre-calculated partition hash value, we can automatically
detect inconsistent partitions on every PME.
Great idea, seems this covers all broken synс cases.

It will check alive nodes in case the primary failed immediately
and will check rejoining node once it finished a rebalance (PME on becoming
an owner).
Recovered cluster will be checked on activation PME (or even before that?).
Also, warmed cluster will be still warmed after check.

Have I missed some cases leads to broken sync except bugs?

1) But how to keep this hash?
- It should be automatically persisted on each checkpoint (it should not
require recalculation on restore, snapshots should be covered too) (and
covered by WAL?).
- It should be always available at RAM for every partition (even for cold
partitions never updated/readed on this node) to be immediately used once
all operations done on PME.

Can we have special pages to keep such hashes and never allow their
eviction?

2) PME is a rare operation on production cluster, but, seems, we have to
check consistency in a regular way.
Since we have to finish all operations before the check, should we have
fake PME for maintenance check in this case?

On Mon, Apr 29, 2019 at 4:59 PM Ivan Rakov  wrote:

> Hi Anton,
>
> Thanks for sharing your ideas.
> I think your approach should work in general. I'll just share my concerns
> about possible issues that may come up.
>
> 1) Equality of update counters doesn't imply equality of partitions
> content under load.
> For every update, primary node generates update counter and then update is
> delivered to backup node and gets applied with the corresponding update
> counter. For example, there are two transactions (A and B) that update
> partition X by the following scenario:
> - A updates key1 in partition X on primary node and increments counter to
> 10
> - B updates key2 in partition X on primary node and increments counter to
> 11
> - While A is still updating another keys, B is finally committed
> - Update of key2 arrives to backup node and sets update counter to 11
> Observer will see equal update counters (11), but update of key 1 is still
> missing in the backup partition.
> This is a fundamental problem which is being solved here:
> https://issues.apache.org/jira/browse/IGNITE-10078
> "Online verify" should operate with new complex update counters which take
> such "update holes" into account. Otherwise, online verify may provide
> false-positive inconsistency reports.
>
> 2) Acquisition and comparison of update counters is fast, but partition
> hash calculation is long. We should check that update counter remains
> unchanged after every K keys handled.
>
> 3)
>
> Another hope is that we'll be able to pause/continue scan, for example,
> we'll check 1/3 partitions today, 1/3 tomorrow, and in three days we'll
> check the whole cluster.
>
> Totally makes sense.
> We may find ourselves into a situation where some "hot" partitions are
> still unprocessed, and every next attempt to calculate partition hash fails
> due to another concurrent update. We should be able to track progress of
> validation (% of calculation time wasted due to concurrent operations may
> be a good metric, 100% is the worst case) and provide option to stop/pause
> activity.
> I think, pause should return an "intermediate results report" with
> information about which partitions have been successfully checked. With
> such report, we can resume activity later: partitions from report will be
> just skipped.
>
> 4)
>
> Since "Idle verify" uses regular pagmem, I assume it replaces hot data
> with persisted.
> So, we have to warm up the cluster after each check.
> Are there any chances to check without cooling the cluster?
>
> I don't see an easy way to achieve it with our page memory architecture.
> We definitely can't just read pages from disk directly: we need to
> synchronize page access with concurrent update operations and checkpoints.
> From my point of view, the correct way to solve this issue is improving
> our page replacement [1] mechanics by making it truly scan-resistant.
>
> P. S. There's another possible way of achieving online verify: instead of
> on-demand hash calculation, we can always keep up-to-date hash value for
> every partition. We'll need to update hash on every insert/update/remove
> operation, but there will be no reordering issues as per function that we
> use for aggregating hash results (+) is commutative. With having
> pre-calculated partition hash value, we can automatically detect
> inconsistent partitions on every PME. What do you think?
>
> [1] -
> https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Durable+Memory+-+under+the+hood#IgniteDurableMemory-underthehood-Pagereplacement(rotationwithdisk)
>
> Best Regards,
> Ivan Rakov
>
> On 29.04.2019 12:20, Anton Vinogradov wrote:
>
> Igniters and especially Ivan Rakov,
>
> "Idle verify" [1] is a really cool tool, to make sure that cluster is
> consistent.

Re: "Idle verify" to "Online verify"

[Ivan Rakov]

Hi Anton,

Thanks for sharing your ideas.
I think your approach should work in general. I'll just share my 
concerns about possible issues that may come up.


1) Equality of update counters doesn't imply equality of partitions 
content under load.
For every update, primary node generates update counter and then update 
is delivered to backup node and gets applied with the corresponding 
update counter. For example, there are two transactions (A and B) that 
update partition X by the following scenario:

- A updates key1 in partition X on primary node and increments counter to 10
- B updates key2 in partition X on primary node and increments counter to 11
- While A is still updating another keys, B is finally committed
- Update of key2 arrives to backup node and sets update counter to 11
Observer will see equal update counters (11), but update of key 1 is 
still missing in the backup partition.
This is a fundamental problem which is being solved here: 
https://issues.apache.org/jira/browse/IGNITE-10078
"Online verify" should operate with new complex update counters which 
take such "update holes" into account. Otherwise, online verify may 
provide false-positive inconsistency reports.


2) Acquisition and comparison of update counters is fast, but partition 
hash calculation is long. We should check that update counter remains 
unchanged after every K keys handled.


3)

Another hope is that we'll be able to pause/continue scan, for 
example, we'll check 1/3 partitions today, 1/3 tomorrow, and in three 
days we'll check the whole cluster.

Totally makes sense.
We may find ourselves into a situation where some "hot" partitions are 
still unprocessed, and every next attempt to calculate partition hash 
fails due to another concurrent update. We should be able to track 
progress of validation (% of calculation time wasted due to concurrent 
operations may be a good metric, 100% is the worst case) and provide 
option to stop/pause activity.
I think, pause should return an "intermediate results report" with 
information about which partitions have been successfully checked. With 
such report, we can resume activity later: partitions from report will 
be just skipped.


4)

Since "Idle verify" uses regular pagmem, I assume it replaces hot data 
with persisted.

So, we have to warm up the cluster after each check.
Are there any chances to check without cooling the cluster?
I don't see an easy way to achieve it with our page memory architecture. 
We definitely can't just read pages from disk directly: we need to 
synchronize page access with concurrent update operations and checkpoints.
From my point of view, the correct way to solve this issue is improving 
our page replacement [1] mechanics by making it truly scan-resistant.


P. S. There's another possible way of achieving online verify: instead 
of on-demand hash calculation, we can always keep up-to-date hash value 
for every partition. We'll need to update hash on every 
insert/update/remove operation, but there will be no reordering issues 
as per function that we use for aggregating hash results (+) is 
commutative. With having pre-calculated partition hash value, we can 
automatically detect inconsistent partitions on every PME. What do you 
think?


[1] - 
https://cwiki.apache.org/confluence/display/IGNITE/Ignite+Durable+Memory+-+under+the+hood#IgniteDurableMemory-underthehood-Pagereplacement(rotationwithdisk)


Best Regards,
Ivan Rakov

On 29.04.2019 12:20, Anton Vinogradov wrote:

Igniters and especially Ivan Rakov,

"Idle verify" [1] is a really cool tool, to make sure that cluster is 
consistent.


1) But it required to have operations paused during cluster check.
At some clusters, this check requires hours (3-4 hours at cases I saw).
I've checked the code of "idle verify" and it seems it possible to 
make it "online" with some assumptions.


Idea:
Currently "Idle verify" checks that partitions hashes, generated this way
while (it.hasNextX()) {
CacheDataRow row = it.nextX();
partHash += row.key().hashCode();
partHash += 
Arrays.hashCode(row.value().valueBytes(grpCtx.cacheObjectContext()));

}
, are the same.

What if we'll generate same pairs updateCounter-partitionHash but will 
compare hashes only in case counters are the same?
So, for example, will ask cluster to generate pairs for 64 partitions, 
then will find that 55 have the same counters (was not updated during 
check) and check them.
The rest (64-55 = 9) partitions will be re-requested and rechecked 
with an additional 55.
This way we'll be able to check cluster is consistent even in сase 
operations are in progress (just retrying modified).


Risks and assumptions:
Using this strategy we'll check the cluster's consistency ... 
eventually, and the check will take more time even on an idle cluster.
In case operationsPerTimeToGeneratePartitionHashes > partitionsCount 
we'll definitely gain no progress.

But, in case of the load is not high, we'll be able to check all cluster.

Another hope is 

"Idle verify" to "Online verify"

[Anton Vinogradov]

Igniters and especially Ivan Rakov,

"Idle verify" [1] is a really cool tool, to make sure that cluster is
consistent.

1) But it required to have operations paused during cluster check.
At some clusters, this check requires hours (3-4 hours at cases I saw).
I've checked the code of "idle verify" and it seems it possible to make it
"online" with some assumptions.

Idea:
Currently "Idle verify" checks that partitions hashes, generated this way
while (it.hasNextX()) {
CacheDataRow row = it.nextX();
partHash += row.key().hashCode();
partHash +=
Arrays.hashCode(row.value().valueBytes(grpCtx.cacheObjectContext()));
}
, are the same.

What if we'll generate same pairs updateCounter-partitionHash but will
compare hashes only in case counters are the same?
So, for example, will ask cluster to generate pairs for 64 partitions, then
will find that 55 have the same counters (was not updated during check) and
check them.
The rest (64-55 = 9) partitions will be re-requested and rechecked with an
additional 55.
This way we'll be able to check cluster is consistent even in сase
operations are in progress (just retrying modified).

Risks and assumptions:
Using this strategy we'll check the cluster's consistency ... eventually,
and the check will take more time even on an idle cluster.
In case operationsPerTimeToGeneratePartitionHashes > partitionsCount we'll
definitely gain no progress.
But, in case of the load is not high, we'll be able to check all cluster.

Another hope is that we'll be able to pause/continue scan, for example,
we'll check 1/3 partitions today, 1/3 tomorrow, and in three days we'll
check the whole cluster.

Have I missed something?

2) Since "Idle verify" uses regular pagmem, I assume it replaces hot data
with persisted.
So, we have to warm up the cluster after each check.
Are there any chances to check without cooling the cluster?

[1]
https://apacheignite-tools.readme.io/docs/control-script#section-verification-of-partition-checksums