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https://issues.apache.org/jira/browse/KUDU-3778?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18083743#comment-18083743
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Daojiang Yan commented on KUDU-3778:
------------------------------------
Gerrit Review: https://gerrit.cloudera.org/c/24326/
> Speed up log block manager startup by replaying small container metadata
> files from memory
> ------------------------------------------------------------------------------------------
>
> Key: KUDU-3778
> URL: https://issues.apache.org/jira/browse/KUDU-3778
> Project: Kudu
> Issue Type: Improvement
> Reporter: Daojiang Yan
> Assignee: Daojiang Yan
> Priority: Major
> Fix For: Backlog
>
>
> *Description*
> On startup,LogBlockContainerNativeMeta::ProcessRecords() replays each
> container's. metadata file through ReadablePBContainerFile::ReadNextPB(),
> which issues two preadv() syscalls per record (one for the length+checksum
> prefix, one for the body+checksum). The total number of read syscalls during
> the "Reading filesystem" phase is therefore O(total records across all
> containers). On a tserver with many containers each holding many records,
> this turns startup into a long stream of tiny sequential reads against the
> kernel.
>
> *Proposal*
> Add an opt-in fast path: when a metadata file's payload fits in a
> configurable budget, read it once into a faststring and let
> ReadablePBContainerFile parse it through an in-memory RandomAccessFile shim
> (MemoryReadableFile). This collapses the per-record preadv() pair into a
> single bulk read per container, so the syscall count during startup drops
> from O(records) to O(containers). Any I/O error during preload, or an
> oversized file, transparently falls back to the existing streaming path, so
> the optimization can only help and never widen the failure envelope of
> startup.
>
> The fast path is gated by
> --log_container_metadata_inmem_replay_threshold_bytes (default 64 MiB;
> runtime/advanced/experimental). Set to 0 to disable. Only applies to
> --block_manager=log with native metadata; encrypted metadata files are
> intentionally left on the streaming path.
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