Sergei Golubchik 979cad2291 MDEV-9531 GROUP_CONCAT with ORDER BY inside takes a lot of memory while it's executed ...

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.

2019-04-24 16:06:54 +02:00

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