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https://issues.apache.org/jira/browse/IGNITE-21084?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Roman Puchkovskiy updated IGNITE-21084:
---
Description:
Client must see the results of a DDL they just executed, no matter through
which node of the cluster a subsequent request is made. To maintain this, we
must make sure that ActivationTimestamp(DDL) becomes non-future on all nodes of
the cluster and only then can we complete the DDL future. As nodes' physical
clocks might have some skew relatively to each other, we add MaxClockSkew to
the timestamp till which we wait to compensate for this difference.
Analogously to HLC.now() being different because its physical part differs on
different nodes, it might be different because *logical* parts are different on
different nodes.
Let's assume we don't have any physical clock skew, and MaxClockSkew is 0.
ActivationTimestamp(DDL) is (100, 5); (100 is physical part, 5 is logical
part). We wait on node 1 (through which the DDL was executed) till its
HLC.now() reaches (100, 5), then we complete the DDL future. The user goes to
node 2 at which HLC.now() is (100, 2). The user executes a query at 'now', and
the query sees the state before the DDL was executed, which breaks our
requirement.
We can fix this by 'rounding' the timestamp-to-wait-for up in the following way:
# If logical part is not 0, increment the physical part and set the logical
part to 0
# If the logical part is 0, leave the timestamp as is
As a result, for (100, 0) we will wait for (100, 0), and at node 1 HLC is at
least (100, 0), so it cannot see the previous schema. For (100, 5) we would
wait till (101, 0), which would also guarantee that a query executed after
waiting sees the new schema version.
> Account for differences of logical part of now() on different nodes when
> waiting after a DDL
>
>
> Key: IGNITE-21084
> URL: https://issues.apache.org/jira/browse/IGNITE-21084
> Project: Ignite
> Issue Type: Improvement
>Reporter: Roman Puchkovskiy
>Assignee: Roman Puchkovskiy
>Priority: Major
> Labels: ignite-3
> Fix For: 3.0.0-beta2
>
>
> Client must see the results of a DDL they just executed, no matter through
> which node of the cluster a subsequent request is made. To maintain this, we
> must make sure that ActivationTimestamp(DDL) becomes non-future on all nodes
> of the cluster and only then can we complete the DDL future. As nodes'
> physical clocks might have some skew relatively to each other, we add
> MaxClockSkew to the timestamp till which we wait to compensate for this
> difference.
> Analogously to HLC.now() being different because its physical part differs on
> different nodes, it might be different because *logical* parts are different
> on different nodes.
> Let's assume we don't have any physical clock skew, and MaxClockSkew is 0.
> ActivationTimestamp(DDL) is (100, 5); (100 is physical part, 5 is logical
> part). We wait on node 1 (through which the DDL was executed) till its
> HLC.now() reaches (100, 5), then we complete the DDL future. The user goes to
> node 2 at which HLC.now() is (100, 2). The user executes a query at 'now',
> and the query sees the state before the DDL was executed, which breaks our
> requirement.
> We can fix this by 'rounding' the timestamp-to-wait-for up in the following
> way:
> # If logical part is not 0, increment the physical part and set the logical
> part to 0
> # If the logical part is 0, leave the timestamp as is
> As a result, for (100, 0) we will wait for (100, 0), and at node 1 HLC is at
> least (100, 0), so it cannot see the previous schema. For (100, 5) we would
> wait till (101, 0), which would also guarantee that a query executed after
> waiting sees the new schema version.
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