[jira] [Created] (IMPALA-15117) Optimize getFirstLevelAcidDirPath

["Michael Smith (Jira)" <ji...@apache.org>]

Michael Smith created IMPALA-15117:
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             Summary: Optimize getFirstLevelAcidDirPath
                 Key: IMPALA-15117
                 URL: https://issues.apache.org/jira/browse/IMPALA-15117
             Project: IMPALA
          Issue Type: Improvement
          Components: Frontend
    Affects Versions: Impala 4.5.0
            Reporter: Michael Smith


This could also apply to Hive.

When loading ACID table metadata, {{AcidUtils.getFirstLevelAcidDirPath}} checks whether each candidate ACID subdirectory name (e.g. {{delta_*}}, {{base_*}}, {{delete_delta_*}}) exists under a partition directory by calling {{FileSystem.isDirectory(path)}} for each candidate in a loop. On distributed filesystems each call is a separate RPC.

Observed via async-profiler on a production Impala catalogd connected to Apache Ozone (OFS): 258 samples (94% blocked on RPC) in the stack {{AcidUtils.getFirstLevelAcidDirPath → FileSystem.isDirectory → OzoneBucket.getFileStatus → OM gRPC call}}. For a partition with N candidate paths, N separate {{GetFileStatus}} RPCs are issued where 1 {{listStatus}} would suffice.

We could replace the N {{isDirectory(candidatePath)}} calls with a single {{listStatus(partitionDir)}} call and resolve membership locally:
# Call {{fs.listStatus(partitionDir)}} once to get all immediate children with their type flags.
# Build a local {{Set<String>}} of child directory names from the result.
# Filter candidate ACID names against the set — no additional RPCs.

This reduces the cost from O(N) RPCs to 1 regardless of filesystem implementation. On object-store-backed filesystems (OFS, S3, ABFS) where each {{isDirectory}} is a synchronous RPC, the reduction is especially significant.



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