[
https://issues.apache.org/jira/browse/HDFS-17166?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Jian Zhang updated HDFS-17166:
------------------------------
Description:
When ns failover， the router may record that the ns have no active namenode,
the router cannot find the active nn in the ns for about 1 minute. The client
will report an error after consuming the number of retries, and the router will
be unable to provide services for the ns for a long time.
11:52:44 Start reporting
!image-2023-08-26-12-06-01-275.png|width=800,height=100!
11:53:46 end reporting
!image-2023-08-26-12-07-47-010.png|width=800,height=20!
At this point, the failover has been successfully completed in the ns, and the
client can directly connect to the active namenode to access it successfully,
but the client cannot access the ns through router for up to a minute
*There is a bug in this logic：*
* A certain ns starts to fail over,
* There is a state where there is no active nn in ns, Router reports the
status (no active nn) to the state store
* After a period of time, the router pulls the state store data to update the
cache, and the cache records that the ns has no active nn
* Failover successfully completed, at which point the ns actually has an
active nn
* Assuming it's not time for router to update the cache yet
* The client sent a request to the router for the ns, and the router accessed
the first nn of the ns in the router’s cache (no active nn)
* Unfortunately, the nn is really standby, so the request went wrong and
entered the exception handling logic. The router found that there is no active
nn for the ns in the cache and throw NoNamenodesAvailableException
* The NoNamenodesAvailableException exception is wrapped as a
RetrieveException, which causes the client to retry. Since each router
retrieves the true standby nn in the cache (because it is always the first one
in the cache and has a high priority), a NoNamenodesAvailableException is
thrown every time until the router updates the cache from the state store
*How to reproduce*
# Suppose we have a ns ns60, which contains 2 nn, nn6001 is active and nn6002
is standby
# Assuming that nn6001 and nn6002 are both in standby state, the priority of
nn6002 is higher than nn6001
# Use default configuration
# Shutdown 2 nn's zkfs, {*}hadoop-daemon.sh stop zkfc{*}, manually perform
failover
# Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
-transitionToStandby --forcemanual nn6001*
# Make sure that the NamenodeHeartbeatService reports that nn6001 is standby
!image-2023-08-26-11-48-22-131.png|width=800,height=20!
# Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
-transitionToActive --forcemanual nn6001*
# The client accesses ns60 through router
!image-2023-08-26-11-56-50-181.png|width=800,height=50!
# After about one minute, request ns60 again through the router
!image-2023-08-26-11-59-25-153.png|width=800,height=50!
# Exceptions are reported for both requests, check the router log
!image-2023-08-26-12-01-39-968.png|width=800,height=20!
# The router cannot respond to the client's request for ns60 for a minute
*Fix the bug*
When an ns in the router's cache does not have an active nn, but in reality,
the ns has an active nn, and the client requests to throw a
NoNamenodesAvailableException, it is proven that the requested nn is a real
standby nn. The priority of this nn should be lowered so that the next request
will find the real active nn, avoiding constantly requesting the real standby
nn, which will cause the cache to be updated before the next time, The router
is unable to provide services for the ns to the client.
*Test my patch*
*1. Unit testing*
*2. Comparison test*
* Suppose we have 2 clients [c1 c2], 2 routers [r1 r2] and a ns [ns60], the ns
has 2 nn [nn6001 nn6002]
* If both nn6001 and nn6002 are in standby state, the priority of nn6002 is
higher than nn6001,
* r1 uses the package that fixing the bug, r2 uses the original package which
has the bug
* c1 loops to send requests to r1, and c2 loops to send requests to r2, the
request is related to ns60
* Make both nn6001 and nn6002 in standby state
* After the router reports that nn is in standby state, switch nn6001 to active
*14:15:24* nn6001 is active
!image-2023-08-26-22-45-46-814.png|width=800,height=120!
* Check the log of router r1, after nn6001 switches to active, only
NoNamenodesAvailableException is printed once
!image-2023-08-26-22-47-22-276.png|width=800,height=30!
* Check the log of router r2, and print NoNamenodesAvailableException for more
than one minute after nn6001 switches to active
!image-2023-08-26-22-47-41-988.png|width=800,height=150!
* At 14:16:25, the client c2 accessing the router with the bug could not get
the data, and the client c1 accessing the router after the bug was fixed could
get the data normally:
c2's log:unable to access normally
!image-2023-08-26-22-48-02-086.png|width=800,height=50!
c1's log:display the result correctly
!image-2023-08-26-22-48-12-352.png|width=800,height=150!
was:
When ns failover， the router may record that the ns have no active namenode,
the router cannot find the active nn in the ns for about 1 minute. The client
will report an error after consuming the number of retries, and the router will
be unable to provide services for the ns for a long time.
11:52:44 Start reporting
!image-2023-08-26-12-06-01-275.png|width=800,height=100!
11:53:46 end reporting
!image-2023-08-26-12-07-47-010.png|width=800,height=20!
At this point, the failover has been successfully completed in the ns, and the
client can directly connect to the active namenode to access it successfully,
but the client cannot access the ns through router for up to a minute
*There is a bug in this logic：*
* A certain ns starts to fail over,
* There is a state where there is no active nn in ns, Router reports the
status (no active nn) to the state store
* After a period of time, the router pulls the state store data to update the
cache, and the cache records that the ns has no active nn
* Failover successfully completed, at which point the ns actually has an
active nn
* Assuming it's not time for router to update the cache yet
* The client sent a request to the router for the ns, and the router accessed
the first nn of the ns in the router’s cache (no active nn)
* Unfortunately, the nn is really standby, so the request went wrong and
entered the exception handling logic. The router found that there is no active
nn for the ns in the cache and throw NoNamenodesAvailableException
* The NoNamenodesAvailableException exception is wrapped as a
RetrieveException, which causes the client to retry. Since each router
retrieves the true standby nn in the cache (because it is always the first one
in the cache and has a high priority), a NoNamenodesAvailableException is
thrown every time until the router updates the cache from the state store
*How to reproduce*
# Suppose we have a ns ns60, which contains 2 nn, nn6001 is active and nn6002
is standby
# Assuming that nn6001 and nn6002 are both in standby state, the priority of
nn6002 is higher than nn6001
# Use default configuration
# Shutdown 2 nn's zkfs, {*}hadoop-daemon.sh stop zkfc{*}, manually perform
failover
# Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
-transitionToStandby --forcemanual nn6001*
# Make sure that the NamenodeHeartbeatService reports that nn6001 is standby
!image-2023-08-26-11-48-22-131.png|width=800,height=20!
# Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
-transitionToActive --forcemanual nn6001*
# The client accesses ns60 through router
!image-2023-08-26-11-56-50-181.png|width=800,height=50!
# After about one minute, request ns60 again through the router
!image-2023-08-26-11-59-25-153.png|width=800,height=50!
# Exceptions are reported for both requests, check the router log
!image-2023-08-26-12-01-39-968.png|width=800,height=20!
# The router cannot respond to the client's request for ns60 for a minute
*Fix the bug*
When an ns in the router's cache does not have an active nn, but in reality,
the ns has an active nn, and the client requests to throw a
NoNamenodesAvailableException, it is proven that the requested nn is a real
standby nn. The priority of this nn should be lowered so that the next request
will find the real active nn, avoiding constantly requesting the real standby
nn, which will cause the cache to be updated before the next time, The router
is unable to provide services for the ns to the client.
> RBF: Throwing NoNamenodesAvailableException for a long time, when failover
> --------------------------------------------------------------------------
>
> Key: HDFS-17166
> URL: https://issues.apache.org/jira/browse/HDFS-17166
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Jian Zhang
> Priority: Major
> Labels: pull-request-available
> Attachments: HDFS-17166.001.patch, HDFS-17166.002.patch,
> image-2023-08-26-11-48-22-131.png, image-2023-08-26-11-56-50-181.png,
> image-2023-08-26-11-59-25-153.png, image-2023-08-26-12-01-39-968.png,
> image-2023-08-26-12-06-01-275.png, image-2023-08-26-12-07-47-010.png,
> image-2023-08-26-22-45-46-814.png, image-2023-08-26-22-47-22-276.png,
> image-2023-08-26-22-47-41-988.png, image-2023-08-26-22-48-02-086.png,
> image-2023-08-26-22-48-12-352.png, screenshot-1.png
>
>
> When ns failover， the router may record that the ns have no active namenode,
> the router cannot find the active nn in the ns for about 1 minute. The client
> will report an error after consuming the number of retries, and the router
> will be unable to provide services for the ns for a long time.
> 11:52:44 Start reporting
> !image-2023-08-26-12-06-01-275.png|width=800,height=100!
> 11:53:46 end reporting
> !image-2023-08-26-12-07-47-010.png|width=800,height=20!
>
> At this point, the failover has been successfully completed in the ns, and
> the client can directly connect to the active namenode to access it
> successfully, but the client cannot access the ns through router for up to a
> minute
>
> *There is a bug in this logic：*
> * A certain ns starts to fail over,
> * There is a state where there is no active nn in ns, Router reports the
> status (no active nn) to the state store
> * After a period of time, the router pulls the state store data to update
> the cache, and the cache records that the ns has no active nn
> * Failover successfully completed, at which point the ns actually has an
> active nn
> * Assuming it's not time for router to update the cache yet
> * The client sent a request to the router for the ns, and the router
> accessed the first nn of the ns in the router’s cache (no active nn)
> * Unfortunately, the nn is really standby, so the request went wrong and
> entered the exception handling logic. The router found that there is no
> active nn for the ns in the cache and throw NoNamenodesAvailableException
> * The NoNamenodesAvailableException exception is wrapped as a
> RetrieveException, which causes the client to retry. Since each router
> retrieves the true standby nn in the cache (because it is always the first
> one in the cache and has a high priority), a NoNamenodesAvailableException is
> thrown every time until the router updates the cache from the state store
>
> *How to reproduce*
> # Suppose we have a ns ns60, which contains 2 nn, nn6001 is active and
> nn6002 is standby
> # Assuming that nn6001 and nn6002 are both in standby state, the priority of
> nn6002 is higher than nn6001
> # Use default configuration
> # Shutdown 2 nn's zkfs, {*}hadoop-daemon.sh stop zkfc{*}, manually perform
> failover
> # Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
> -transitionToStandby --forcemanual nn6001*
> # Make sure that the NamenodeHeartbeatService reports that nn6001 is standby
> !image-2023-08-26-11-48-22-131.png|width=800,height=20!
> # Manually switch nn6001 active->standby, *hdfs haadmin -ns ns60
> -transitionToActive --forcemanual nn6001*
> # The client accesses ns60 through router
> !image-2023-08-26-11-56-50-181.png|width=800,height=50!
> # After about one minute, request ns60 again through the router
> !image-2023-08-26-11-59-25-153.png|width=800,height=50!
> # Exceptions are reported for both requests, check the router log
> !image-2023-08-26-12-01-39-968.png|width=800,height=20!
> # The router cannot respond to the client's request for ns60 for a minute
>
>
> *Fix the bug*
> When an ns in the router's cache does not have an active nn, but in reality,
> the ns has an active nn, and the client requests to throw a
> NoNamenodesAvailableException, it is proven that the requested nn is a real
> standby nn. The priority of this nn should be lowered so that the next
> request will find the real active nn, avoiding constantly requesting the real
> standby nn, which will cause the cache to be updated before the next time,
> The router is unable to provide services for the ns to the client.
>
> *Test my patch*
> *1. Unit testing*
> *2. Comparison test*
> * Suppose we have 2 clients [c1 c2], 2 routers [r1 r2] and a ns [ns60], the
> ns has 2 nn [nn6001 nn6002]
> * If both nn6001 and nn6002 are in standby state, the priority of nn6002 is
> higher than nn6001,
> * r1 uses the package that fixing the bug, r2 uses the original package
> which has the bug
> * c1 loops to send requests to r1, and c2 loops to send requests to r2, the
> request is related to ns60
> * Make both nn6001 and nn6002 in standby state
> * After the router reports that nn is in standby state, switch nn6001 to
> active
> *14:15:24* nn6001 is active
> !image-2023-08-26-22-45-46-814.png|width=800,height=120!
> * Check the log of router r1, after nn6001 switches to active, only
> NoNamenodesAvailableException is printed once
> !image-2023-08-26-22-47-22-276.png|width=800,height=30!
>
> * Check the log of router r2, and print NoNamenodesAvailableException for
> more than one minute after nn6001 switches to active
> !image-2023-08-26-22-47-41-988.png|width=800,height=150!
>
> * At 14:16:25, the client c2 accessing the router with the bug could not get
> the data, and the client c1 accessing the router after the bug was fixed
> could get the data normally:
> c2's log:unable to access normally
> !image-2023-08-26-22-48-02-086.png|width=800,height=50!
> c1's log:display the result correctly
> !image-2023-08-26-22-48-12-352.png|width=800,height=150!
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