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https://issues.apache.org/jira/browse/CALCITE-4994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17482665#comment-17482665
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Julian Hyde commented on CALCITE-4994:
--------------------------------------
If you need to build and cache a map from name to integer, the best way might
be sub-class of {{SqlNameMatcher}} that contains a Guava cache:
{code}
static final int THRESHOLD = 20;
final LoadingCache<RelDataType, Map<String, Integer>> cache = ...;
@Override @Nullable RelDataTypeField field(RelDataType rowType, String
fieldName) {
if (rowType.getFieldCount() < THRESHOLD) {
return super.field(rowType, fieldName);
}
Integer i = cache.get(rowType).get(fieldName);
return i == null ? null : rowType.getFields().get(i);
}
{code}
Or maybe override {{SqlNameMatcher.indexOf}} rather than {{field}}.
This {{SqlNameMatcher}} instance would be stateful so we need to be careful. It
would be allocated and stored inside a {{CalciteCatalogReader}}, so its
lifetime would not be longer than a single query or type factory. Other places
in the preparation process that need to access fields by name would also
benefit.
> SqlToRelConverter creates FieldMap for every Identifier Instead of Memoizing
> it
> -------------------------------------------------------------------------------
>
> Key: CALCITE-4994
> URL: https://issues.apache.org/jira/browse/CALCITE-4994
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Jay Narale
> Priority: Major
> Labels: pull-request-available
> Time Spent: 0.5h
> Remaining Estimate: 0h
>
> When converting from Sql To Rel, In SqlToRelConverter for every single
> instance of an identifier we create a new map in
> *_org.apache.calcite.sql2rel.SqlToRelConverter.Blackboard#lookupExp_*
>
> {code:java}
> final Map<String, Integer> fieldOffsets = new HashMap<>();
> for (RelDataTypeField f : resolve.rowType().getFieldList()) {
> if (!fieldOffsets.containsKey(f.getName())) {
> fieldOffsets.put(f.getName(), f.getIndex());
> }
> }
> final Map<String, Integer> map = ImmutableMap.copyOf(fieldOffsets);{code}
>
> So for a Sql Query
> {code:java}
> SELECT name, nation FROM customer{code}
> We would do the above operation twice.
> Memoization of this information will improve performance.
> In my database, I had observed that for a large table involving 1200 columns
> and a huge select having multiple expressions and operators, this part was a
> bottleneck.
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