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Posted to issues@kudu.apache.org by "Grant Henke (Jira)" <ji...@apache.org> on 2020/06/03 14:39:00 UTC
[jira] [Updated] (KUDU-2731) Getting column schema information from
KuduSchema requires copying a KuduColumnSchema object
[ https://issues.apache.org/jira/browse/KUDU-2731?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Grant Henke updated KUDU-2731:
------------------------------
Component/s: perf
> Getting column schema information from KuduSchema requires copying a KuduColumnSchema object
> --------------------------------------------------------------------------------------------
>
> Key: KUDU-2731
> URL: https://issues.apache.org/jira/browse/KUDU-2731
> Project: Kudu
> Issue Type: Improvement
> Components: perf
> Affects Versions: 1.9.0
> Reporter: William Berkeley
> Priority: Major
>
> I'm looking at a CPU profile of Impala inserting into Kudu. {{KuduTableSink::Send}} has code that schematically does the following:
> {noformat}
> for each row in the batch
> for each column
> if (schema.Column(col_idx).isNullable()) {
> write->mutable_row()->SetNull(col);
> }
> }
> }
> {noformat}
> See [kudu-table-sink.cc|https://github.com/apache/impala/blob/branch-3.1.0/be/src/exec/kudu-table-sink.cc#L236]. However, {{KuduSchema::Column}} copies the column schema and returns it by value, so the if statement constructs and destroys a column schema object just to check if the column is nullable.
> This is by far the biggest user of CPU in the Impala process (35% or so). The workload might be I/O bound writing to Kudu anyway, though. Nevertheless, we should provide a way to avoid this copying in the API, either by adding a method like
> {noformat}
> class KuduSchema {
> const KuduColumnSchema& get_column(int idx);
> }
> {noformat}
> or a method like
> {noformat}
> class KuduSchema {
> bool is_column_nullable(int idx);
> }
> {noformat}
> The former is the most flexible while the latter frees the client from worrying about holding the ref longer than the KuduColumnSchema object lives. We might need to add a number of methods similar to the latter method to cover other potentially useful things like checking encoding, type, etc.
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