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https://issues.apache.org/jira/browse/HIVE-16143?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on HIVE-16143 started by Vihang Karajgaonkar.
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> Improve msck repair batching
> ----------------------------
>
> Key: HIVE-16143
> URL: https://issues.apache.org/jira/browse/HIVE-16143
> Project: Hive
> Issue Type: Improvement
> Reporter: Vihang Karajgaonkar
> Assignee: Vihang Karajgaonkar
>
> Currently, the {{msck repair table}} command batches the number of partitions
> created in the metastore using the config {{HIVE_MSCK_REPAIR_BATCH_SIZE}}.
> Following snippet shows the batching logic. There can be couple of
> improvements to this batching logic:
> {noformat}
> int batch_size = conf.getIntVar(ConfVars.HIVE_MSCK_REPAIR_BATCH_SIZE);
> if (batch_size > 0 && partsNotInMs.size() > batch_size) {
> int counter = 0;
> for (CheckResult.PartitionResult part : partsNotInMs) {
> counter++;
>
> apd.addPartition(Warehouse.makeSpecFromName(part.getPartitionName()), null);
> repairOutput.add("Repair: Added partition to metastore " +
> msckDesc.getTableName()
> + ':' + part.getPartitionName());
> if (counter % batch_size == 0 || counter ==
> partsNotInMs.size()) {
> db.createPartitions(apd);
> apd = new AddPartitionDesc(table.getDbName(),
> table.getTableName(), false);
> }
> }
> } else {
> for (CheckResult.PartitionResult part : partsNotInMs) {
>
> apd.addPartition(Warehouse.makeSpecFromName(part.getPartitionName()), null);
> repairOutput.add("Repair: Added partition to metastore " +
> msckDesc.getTableName()
> + ':' + part.getPartitionName());
> }
> db.createPartitions(apd);
> }
> } catch (Exception e) {
> LOG.info("Could not bulk-add partitions to metastore; trying one by
> one", e);
> repairOutput.clear();
> msckAddPartitionsOneByOne(db, table, partsNotInMs, repairOutput);
> }
> {noformat}
> 1. If the batch size is too aggressive the code falls back to adding
> partitions one by one which is almost always very slow. It is easily possible
> that users increase the batch size to higher value to make the command run
> faster but end up with a worse performance because code falls back to adding
> one by one. Users are then expected to determine the tuned value of batch
> size which works well for their environment. I think the code could handle
> this situation better by exponentially decaying the batch size instead of
> falling back to one by one.
> 2. The other issue with this implementation is if lets say first batch
> succeeds and the second one fails, the code tries to add all the partitions
> one by one irrespective of whether some of the were successfully added or
> not. If we need to fall back to one by one we should atleast remove the ones
> which we know for sure are already added successfully.
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