[fix](statistics)Control memory use for sample partition column and key column. (#46534) #48927
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…ey column. (apache#46534) When doing sample analyze for partition column and key column, BE may encounter OOM problem. The reason is, partition column need to choose at least one tablet in each partition to calculate the NDV and couldn't use limit in the SQL, so when the table has large number of partitions and each tablet in each partition is quite large, the sample SQL may try to read too many data which will cause BE OOM. Similarly, key column couldn't use limit as well, so when one tablet is very large, it also could cause OOM. This pr is try to solve this problem. For partition columns, when the selected tablets contain more than 1000000000 (one billion) rows, we use ndv() function to read up to 5 partitions to get the NDV value of this 5 partitions, say the ndv is n. Suppose the row count in the 5 partitions is r, and the row count of tje table is R, the table NDV would be n * R / r. ndv() function use hll, so it only use a small amount of memory. For key columns, when the selected tablets contain more than 1000000000 rows, we use limit 1000000000 to control the rows to read. Reading 1000000000 rows would use at most 8GB memory in BE, which is acceptable. Issue Number: close #xxx Related PR: #xxx Problem Summary: None
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Thank you for your contribution to Apache Doris. Please clearly describe your PR:
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yiguolei
approved these changes
Mar 14, 2025
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backport: #46534