[IMPALA-6670] Executor-only impalads do not refresh their lib-cache entries

• Type: Bug
• Status: Resolved
• Priority: Blocker
• Resolution: Fixed
• Affects Version/s: Impala 2.9.0, Impala 2.10.0, Impala 2.11.0, Impala 3.0, Impala 2.12.0, Impala 2.13.0
• Fix Version/s: Impala 3.0, Impala 2.12.0
• Component/s: Backend, Frontend
• Target Version: Impala 3.0, Impala 2.13.0
• Epic Color: ghx-label-5
• Assignee: Vuk Ercegovac
• Reporter: Vuk Ercegovac
• Created: 14/Mar/18 23:59
• Updated: 31/Jul/19 22:19
• Resolved: 23/Mar/18 21:47

Description

When impalads are only executors, there is no way for their lib-cache entries to be refreshed. As far as I can tell, the version of the cached file will remain the same until the impalad is restarted (and a query with a udf/uda that references that file is eval'd on that node).

In contrast, impalads that are both executors and coordinators will receive metadata updates which will result in the cache entry being refreshed. Even in this mode, there is room for inconsistency (e.g., update the jar between coordination and evaluation), but all impalads can be made to converge.

Basic steps to repro:

• Make two jars (I used impala-hive-udfs.jar), one with TestUdf.class and the other with TestUdf.class + ReplaceStringUdf.class
• Clear the state

drop function scratch.identity(boolean);
drop function scratch.replace_string(string);

• cp part1.jar to tmp.jar

hadoop fs -cp -f /test-warehouse/scratch.db/part1.jar /test-warehouse/scratch.db/tmp.jar

• create identity from tmp.jar

create function scratch.identity(boolean) returns boolean
location '/test-warehouse/scratch.db/tmp.jar'
symbol='org.apache.impala.TestUdf';

• Run a query on all nodes

select count( *) from functional.alltypes where scratch.identity(bool_col) = bool_col;

• cp part2.jar to tmp.jar

hadoop fs -cp -f /test-warehouse/scratch.db/part2.jar /test-warehouse/scratch.db/tmp.jar

• create replace_string function

create function scratch.replace_string(string) returns string
location '/test-warehouse/scratch.db/tmp.jar'
symbol='org.apache.impala.ReplaceStringUdf';

• run a query

select count( *) from functional.alltypes where scratch.replace_string(string_col) = string_col;

When all impalads are both executors and coordinators, the second query works.

With:

./bin/start-impala-cluster.py --num_coordinators=1

The second query always results in:

WARNINGS: ImpalaRuntimeException: Unable to find class.
CAUSED BY: ClassNotFoundException: org.apache.impala.ReplaceStringUdf

(each backend still has the previous version of tmp.jar)

Currently, executors do not need metadata other than what is supplied by coordinators in the plan. Libs are excluded from this scheme; each impalad tries to maintain consistency with the lib files stored in the FS as of the time of function creation (little more complicated ...). 

One option here is that plans include lib version information so that impalads can know when a refresh is needed.

 

Issue Links

• is related to: IMPALA-8763 Dedicated executors not invalidating stale LibCache entries
• relates to: IMPALA-6727 lib-cache use for external datasources