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MDEV-9531 GROUP_CONCAT with ORDER BY inside takes a lot of memory while it's executed

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group concat tree is allocated in a memroot, so the only way to free
memory is to copy a part of the tree into a new memroot.

track the accumilated length of the result, and when it crosses
the threshold  - copy the result into a new tree, free the old one.
This commit is contained in:
Sergei Golubchik
2017-06-21 16:07:54 +02:00
parent e91fd8783a
commit 979cad2291
4 changed files with 109 additions and 4 deletions
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8
mysql-test/r/func_gconcat.result
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@ -1199,3 +1199,11 @@ Warning 1260 Row 3 was cut by GROUP_CONCAT()
Warning 1260 Row 5 was cut by GROUP_CONCAT()
DROP TABLE t1;
SET group_concat_max_len= DEFAULT;
set max_session_mem_used=16*1024*1024;
SELECT GROUP_CONCAT(concat(seq/1.1), concat(seq/1.1), concat(seq/1.1), concat(seq/1.1), concat(seq/1.1), concat(seq/1.1), concat(seq/1.1), concat(seq/1.1) ORDER BY 2,1,3,4,6,5,8,7) AS c
FROM seq_1_to_200000;
c
0.90910.90910.90910.90910.90910.90910.90910.9091,1.81821.81821.81821.81821.81821.81821.81821.8182,10.000010.000010.000010.000010.000010.000010.000010.0000,10.909110.909110.909110.909110.909110.909110.909110.9091,100.0000100.0000100.0000100.0000100.0000100.0000100.0000100.0000,100.9091100.9091100.9091100.9091100.9091100.9091100.9091100.9091,1000.00001000.00001000.00001000.00001000.00001000.00001000.00001000.0000,1000.90911000.90911000.90911000.90911000.90911000.90911000.90911000.9091,10000.000010000.000010000.000010000.000010000.000010000.000010000.000010000.0000,10000.909110000.909110000.909110000.909110000.909110000.909110000.909110000.9091,100000.0000100000.0000100000.0000100000.0000100000.0000100000.0000100000.0000100000.0000,100000.9091100000.9091100000.9091100000.9091100000.9091100000.9091100000.9091100000.9091,100001.8182100001.8182100001.8182100001.8182100001.8182100001.8182100001.8182100001.8182,100002.7273100002.7273100002.7273100002.7273100002.7273100002.7273100002.7273100002.7273,100003.6364100003.
Warnings:
Warning 1260 Row 15 was cut by GROUP_CONCAT()
set max_session_mem_used=default;