Details
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Improvement
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Status: Resolved
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Major
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Resolution: Won't Fix
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7.5
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None
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None
Description
Delta imports in DataImportHandler is sometimes slower than full imports where the delta import makes multiple queries compare to full import and hence making it time complex. Listed in: https://wiki.apache.org/solr/DataImportHandlerDeltaQueryViaFullImport
In the mailing list; http://lucene.472066.n3.nabble.com/Number-of-requests-spike-up-when-i-do-the-delta-Import-td4338162.html one of the Solr users have noted a workaround which works perfectly and improves delta import performance, where we need to specify ${dataimporter.last_index_time} in the delta_import_query, and not delta_query.
I found a hacky way to limit the number of times deltaImportQuery was executed. As designed, solr executes deltaQuery to get a list of ids that need to be indexed. For each of those, it executes deltaImportQuery, which is typically very similar to the full query. I constructed a deltaQuery to purposely only return 1 row. E.g. deltaQuery = "SELECT id FROM table WHERE rownum=1" // written for oracle, likely requires a different syntax for other dbs. Also, it occurred to you could probably include the date>= '${dataimporter.last_index_time}' filter here so this returns 0 rows if no data has changed Since deltaImportQuery now *only gets called once I needed to add the filter logic to *deltaImportQuery *to only select the changed rows (that logic is normally in *deltaQuery). E.g. deltaImportQuery = [normal import query] WHERE date >= '${dataimporter.last_index_time}'
A number of other users have adopted the strategy and DIH delta import performance has improved, and henceforth documenting this strategy as TIP will help other users too.
Attachments
Issue Links
- is superceded by
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SOLR-14783 Remove DIH from 9.0
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- Closed
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