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Posted to jira@kafka.apache.org by "Luke Chen (Jira)" <ji...@apache.org> on 2021/03/15 04:23:00 UTC
[jira] [Updated] (KAFKA-12464) Enhance constrained sticky Assign
algorithm
[ https://issues.apache.org/jira/browse/KAFKA-12464?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Luke Chen updated KAFKA-12464:
------------------------------
Description:
In KAFKA-9987, we did a great improvement for the case when all consumers were subscribed to same set of topics. The algorithm contains 4 phases:
# Reassign as many previously owned partitions as possible, up to the maxQuota
# Fill remaining members up to minQuota
# If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
# Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
Take an example for better understanding:
*example:*
Current status: 2 consumers (C0, C1), and 10 topic partitions: t1p0, t1p1, ... t1p9
Suppose, current assignment is:
_C0: t1p0, t1p1, t1p2, t1p3, t1p4_
_C1: t1p5, t1p6, t1p7, t1p8, t1p9_
Now, new consumer added: C2, so we'll do:
# Reassign as many previously owned partitions as possible, up to the maxQuota
After this phase, the assignment will be: (maxQuota will be 4)
_C0: t1p0, t1p1, t1p2, t1p3_
_C1: t1p5, t1p6, t1p7, t1p8_
# Fill remaining members up to minQuota
After this phase, the assignment will be:
_C0: t1p0, t1p1, t1p2, t1p3_
_C1: t1p5, t1p6, t1p7, t1p8_
_C2: t1p4, t1p9_
# If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
After this phase, the assignment will be:
_C0: t1p0, t1p1, t1p2_
_C1: t1p5, t1p6, t1p7, t1p8_
_C2: t1p4, t1p9,_ _t1p3_
# Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
As we can see, we need 3 phases to complete the assignment. But we can actually completed with 2 phases. Here's the updated algorithm:
# Reassign as many previously owned partitions as possible, up to the maxQuota, and also considering the numMaxQuota by the remainder of (Partitions / Consumers)
# Fill remaining members up to numMaxQuota, and others to minQuota
By considering the numMaxQuota, the original step 1 won't be too aggressive to assign too many partitions to consumers, and the step 2 won't be too conservative to assign not enough partitions to consumers, so that we don't need step 3 and step 4 to balance them.
{{So, the updated Pseudo-code sketch of the algorithm:}}
{{ {{C_f := (P/N)_floor, the floor capacity aaa}}}}
{{{{C_c := (P/N)_ceil, the ceiling capacity}}}}
{{{{*C_r := (P%N) the allowed number of members with C_c partitions assigned*}}}}
{{*num_max_capacity_members := current number of members with C_c partitions assigned (default to 0)*}}
{{ }}
{{ {{members := the sorted set of all consumers}}}}
{{ {{partitions := the set of all partitions}}}}
{{ {{unassigned_partitions := the set of partitions not yet assigned, initialized to be all partitions}}}}
{{ {{unfilled_members := the set of consumers not yet at capacity, initialized to empty}}}}
{{ -{{max_capacity_members := the set of members with exactly C_c partitions assigned, initialized to empty}}-}}
{{ {{member.owned_partitions := the set of previously owned partitions encoded in the Subscription}}}}
{{ }}
{{ {{// Reassign as many previously owned partitions as possible, *by considering the num_max_capacity_members* }}}}
{{ {{for member : members}}}}
{{ {{ }}{{remove any partitions that are no longer in the subscription from its owned partitions}}}}
{{ {{ }}{{remove all owned_partitions if the generation is old}}}}
{{ {{ }}{{if member.owned_partitions.size < C_f}}}}
{{ {{ }}{{assign all owned partitions to member and remove from unassigned_partitions}}}}
{{ {{ }}{{add member to unfilled_members}}}}
{{ {{ }}-{{else if member.owned_partitions.size == C_f}}-}}
{{ -{{ }}{{assign first C_f owned_partitions to member and remove from unassigned_partitions}}-}}
{{ {{ }}*{{else if }}{{member.owned_partitions.size >= C_c && num_max_capacity_members < C_r}}*}}
{{ {{ }}{{assign first C_c owned_partitions to member and remove from unassigned_partitions}}}}{{ *num_max_capacity_members*++}}
{{ {{ }}-{{add member to max_capacity_members}}-}}{{ {{else }}}}
{{ {{ }}{{assign first C_f owned_partitions to member and remove from unassigned_partitions}}}}
{{ }}
{{ {{sort unassigned_partitions in partition order, ie t0_p0, t1_p0, t2_p0, t0_p1, t1_p0 .... (for data parallelism)}}}}
{{ {{sort unfilled_members by memberId (for determinism)}}}}
{{ }}
{{ {{// Fill remaining members up to *the C_r numbers of C_c, otherwise, to C_f*}}}}
{{ {{for member : unfilled_members}}}}
{{ {{ }}{{compute the remaining capacity as -C = C_f - num_assigned_partitions- }}}}{{{{ }}}}
{{{{ if *num_max_capacity_members < C_r*: }}}}{{{{ }}}}
{{{{ C = C_c - }}{{num_assigned_partitions}}}}{{{{ ** }}}}
{{{{ *num_max_capacity_members*}}{{++}}}}
{{{{ else }}}}
{{{{ C = C_f - num_assigned_partitions}}}}
{{ {{ }}{{pop the first C partitions from unassigned_partitions and assign to member}}}}
{{ }}
{{ -{{// Steal partitions from members with max_capacity if necessary}}-}}
{{ -{{if we run out of partitions before getting to the end of unfilled members:}}-}}
{{ -{{ }}{{for member : unfilled_members}}-}}
{{ -{{ }}{{poll for first member in max_capacity_members and remove one partition}}-}}
{{ -{{ }}{{assign this partition to the unfilled member}}-}}
{{ -{{ }}- }}
{{ -{{// Distribute remaining partitions, one per consumer, to fill some up to C_c if necessary}}-}}
{{ -{{if we run out of unfilled_members before assigning all partitions:}}-}}
{{ -{{ }}{{for partition : unassigned_partitions}}-}}
{{ -{{ }}{{assign to next member in members that is not in max_capacity_members (then add member to max_capacity_members)}}-}}
{code:java}
C_f := (P/N)_floor, the floor capacity
C_c := (P/N)_ceil, the ceiling capacity
C_r := (P%N) the allowed number of members with C_c partitions assigned
num_max_capacity_members := current number of members with C_c partitions assigned (default to 0)
members := the sorted set of all consumers
partitions := the set of all partitions
unassigned_partitions := the set of partitions not yet assigned, initialized to be all partitions
unfilled_members := the set of consumers not yet at capacity, initialized to empty
member.owned_partitions := the set of previously owned partitions encoded in the Subscription
// Reassign as many previously owned partitions as possible, by considering the num_max_capacity_members
for member : members
remove any partitions that are no longer in the subscription from its owned partitions
remove all owned_partitions if the generation is old
if member.owned_partitions.size < C_f
assign all owned partitions to member and remove from unassigned_partitions
add member to unfilled_members
else if member.owned_partitions.size >= C_c && num_max_capacity_members < C_r
assign first C_c owned_partitions to member and remove from unassigned_partitions
num_max_capacity_members++
add member to max_capacity_members
else
assign first C_f owned_partitions to member and remove from unassigned_partitions
sort unassigned_partitions in partition order, ie t0_p0, t1_p0, t2_p0, t0_p1, t1_p0 .... (for data parallelism)
sort unfilled_members by memberId (for determinism)
// Fill remaining members up to the C_r numbers of C_c, otherwise, to C_f
for member : unfilled_members
compute the remaining capacity as:
if num_max_capacity_members < C_r:
C = C_c - num_assigned_partitions
num_max_capacity_members++
else
C = C_f - num_assigned_partitions
pop the first C partitions from unassigned_partitions and assign to member{code}
was:
In KAFKA-9987, we did a great improvement for the case when all consumers were subscribed to same set of topics. The algorithm contains 4 phases:
# Reassign as many previously owned partitions as possible, up to the maxQuota
# Fill remaining members up to minQuota
# If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
# Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
Take an example for better understanding:
Current status: 2 consumers (C0, C1), and 10 topic partitions: t1p0, t1p1, ... t1p9
Suppose, current assignment is:
_C0: t1p0, t1p1, t1p2, t1p3, t1p4_
_C1: t1p5, t1p6, t1p7, t1p8, t1p9_
New, new consumer added: C2, so we'll do:
# Reassign as many previously owned partitions as possible, up to the maxQuota
# Fill remaining members up to minQuota
# If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
# Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
> Enhance constrained sticky Assign algorithm
> -------------------------------------------
>
> Key: KAFKA-12464
> URL: https://issues.apache.org/jira/browse/KAFKA-12464
> Project: Kafka
> Issue Type: Improvement
> Affects Versions: 2.7.0
> Reporter: Luke Chen
> Assignee: Luke Chen
> Priority: Major
>
> In KAFKA-9987, we did a great improvement for the case when all consumers were subscribed to same set of topics. The algorithm contains 4 phases:
> # Reassign as many previously owned partitions as possible, up to the maxQuota
> # Fill remaining members up to minQuota
> # If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
> # Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
>
> Take an example for better understanding:
> *example:*
> Current status: 2 consumers (C0, C1), and 10 topic partitions: t1p0, t1p1, ... t1p9
> Suppose, current assignment is:
> _C0: t1p0, t1p1, t1p2, t1p3, t1p4_
> _C1: t1p5, t1p6, t1p7, t1p8, t1p9_
> Now, new consumer added: C2, so we'll do:
> # Reassign as many previously owned partitions as possible, up to the maxQuota
> After this phase, the assignment will be: (maxQuota will be 4)
> _C0: t1p0, t1p1, t1p2, t1p3_
> _C1: t1p5, t1p6, t1p7, t1p8_
> # Fill remaining members up to minQuota
> After this phase, the assignment will be:
> _C0: t1p0, t1p1, t1p2, t1p3_
> _C1: t1p5, t1p6, t1p7, t1p8_
> _C2: t1p4, t1p9_
> # If we ran out of unassigned partitions before filling all consumers, we need to start stealing partitions from the over-full consumers at max capacity
> After this phase, the assignment will be:
> _C0: t1p0, t1p1, t1p2_
> _C1: t1p5, t1p6, t1p7, t1p8_
> _C2: t1p4, t1p9,_ _t1p3_
> # Otherwise we may have run out of unfilled consumers before assigning all partitions, in which case we should just distribute one partition each to all consumers at min capacity
>
>
> As we can see, we need 3 phases to complete the assignment. But we can actually completed with 2 phases. Here's the updated algorithm:
> # Reassign as many previously owned partitions as possible, up to the maxQuota, and also considering the numMaxQuota by the remainder of (Partitions / Consumers)
> # Fill remaining members up to numMaxQuota, and others to minQuota
>
> By considering the numMaxQuota, the original step 1 won't be too aggressive to assign too many partitions to consumers, and the step 2 won't be too conservative to assign not enough partitions to consumers, so that we don't need step 3 and step 4 to balance them.
>
> {{So, the updated Pseudo-code sketch of the algorithm:}}
> {{ {{C_f := (P/N)_floor, the floor capacity aaa}}}}
> {{{{C_c := (P/N)_ceil, the ceiling capacity}}}}
> {{{{*C_r := (P%N) the allowed number of members with C_c partitions assigned*}}}}
> {{*num_max_capacity_members := current number of members with C_c partitions assigned (default to 0)*}}
> {{ }}
> {{ {{members := the sorted set of all consumers}}}}
> {{ {{partitions := the set of all partitions}}}}
> {{ {{unassigned_partitions := the set of partitions not yet assigned, initialized to be all partitions}}}}
> {{ {{unfilled_members := the set of consumers not yet at capacity, initialized to empty}}}}
> {{ -{{max_capacity_members := the set of members with exactly C_c partitions assigned, initialized to empty}}-}}
> {{ {{member.owned_partitions := the set of previously owned partitions encoded in the Subscription}}}}
> {{ }}
> {{ {{// Reassign as many previously owned partitions as possible, *by considering the num_max_capacity_members* }}}}
> {{ {{for member : members}}}}
> {{ {{ }}{{remove any partitions that are no longer in the subscription from its owned partitions}}}}
> {{ {{ }}{{remove all owned_partitions if the generation is old}}}}
> {{ {{ }}{{if member.owned_partitions.size < C_f}}}}
> {{ {{ }}{{assign all owned partitions to member and remove from unassigned_partitions}}}}
> {{ {{ }}{{add member to unfilled_members}}}}
> {{ {{ }}-{{else if member.owned_partitions.size == C_f}}-}}
> {{ -{{ }}{{assign first C_f owned_partitions to member and remove from unassigned_partitions}}-}}
> {{ {{ }}*{{else if }}{{member.owned_partitions.size >= C_c && num_max_capacity_members < C_r}}*}}
> {{ {{ }}{{assign first C_c owned_partitions to member and remove from unassigned_partitions}}}}{{ *num_max_capacity_members*++}}
> {{ {{ }}-{{add member to max_capacity_members}}-}}{{ {{else }}}}
> {{ {{ }}{{assign first C_f owned_partitions to member and remove from unassigned_partitions}}}}
> {{ }}
> {{ {{sort unassigned_partitions in partition order, ie t0_p0, t1_p0, t2_p0, t0_p1, t1_p0 .... (for data parallelism)}}}}
> {{ {{sort unfilled_members by memberId (for determinism)}}}}
> {{ }}
> {{ {{// Fill remaining members up to *the C_r numbers of C_c, otherwise, to C_f*}}}}
> {{ {{for member : unfilled_members}}}}
> {{ {{ }}{{compute the remaining capacity as -C = C_f - num_assigned_partitions- }}}}{{{{ }}}}
> {{{{ if *num_max_capacity_members < C_r*: }}}}{{{{ }}}}
> {{{{ C = C_c - }}{{num_assigned_partitions}}}}{{{{ ** }}}}
> {{{{ *num_max_capacity_members*}}{{++}}}}
> {{{{ else }}}}
> {{{{ C = C_f - num_assigned_partitions}}}}
> {{ {{ }}{{pop the first C partitions from unassigned_partitions and assign to member}}}}
> {{ }}
> {{ -{{// Steal partitions from members with max_capacity if necessary}}-}}
> {{ -{{if we run out of partitions before getting to the end of unfilled members:}}-}}
> {{ -{{ }}{{for member : unfilled_members}}-}}
> {{ -{{ }}{{poll for first member in max_capacity_members and remove one partition}}-}}
> {{ -{{ }}{{assign this partition to the unfilled member}}-}}
> {{ -{{ }}- }}
> {{ -{{// Distribute remaining partitions, one per consumer, to fill some up to C_c if necessary}}-}}
> {{ -{{if we run out of unfilled_members before assigning all partitions:}}-}}
> {{ -{{ }}{{for partition : unassigned_partitions}}-}}
> {{ -{{ }}{{assign to next member in members that is not in max_capacity_members (then add member to max_capacity_members)}}-}}
>
> {code:java}
> C_f := (P/N)_floor, the floor capacity
> C_c := (P/N)_ceil, the ceiling capacity
> C_r := (P%N) the allowed number of members with C_c partitions assigned
> num_max_capacity_members := current number of members with C_c partitions assigned (default to 0)
>
> members := the sorted set of all consumers
> partitions := the set of all partitions
> unassigned_partitions := the set of partitions not yet assigned, initialized to be all partitions
> unfilled_members := the set of consumers not yet at capacity, initialized to empty
> member.owned_partitions := the set of previously owned partitions encoded in the Subscription
>
> // Reassign as many previously owned partitions as possible, by considering the num_max_capacity_members
> for member : members
> remove any partitions that are no longer in the subscription from its owned partitions
> remove all owned_partitions if the generation is old
> if member.owned_partitions.size < C_f
> assign all owned partitions to member and remove from unassigned_partitions
> add member to unfilled_members
> else if member.owned_partitions.size >= C_c && num_max_capacity_members < C_r
> assign first C_c owned_partitions to member and remove from unassigned_partitions
> num_max_capacity_members++
> add member to max_capacity_members
> else
> assign first C_f owned_partitions to member and remove from unassigned_partitions
>
> sort unassigned_partitions in partition order, ie t0_p0, t1_p0, t2_p0, t0_p1, t1_p0 .... (for data parallelism)
> sort unfilled_members by memberId (for determinism)
>
> // Fill remaining members up to the C_r numbers of C_c, otherwise, to C_f
> for member : unfilled_members
> compute the remaining capacity as:
> if num_max_capacity_members < C_r:
> C = C_c - num_assigned_partitions
> num_max_capacity_members++
> else
> C = C_f - num_assigned_partitions
> pop the first C partitions from unassigned_partitions and assign to member{code}
>
>
>
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