VACUUM memory management

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От Ibrar Ahmed
Тема VACUUM memory management
Дата
Msg-id CALtqXTdbBKRLdUuekg-2iYN06EX7BrodU1PheNgB6Bx6SuvCvg@mail.gmail.com
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Ответы Re: VACUUM memory management  (Alvaro Herrera <alvherre@2ndquadrant.com>)
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Hi,

The memory consumption of VACUUM has some issues and could be improved. Some of its limitations are recorded in the comments of the “vacuumlazy.c” file. The current design of VACUUM memory usage is that it stores the TID in a fixed-size array which is allocated at the start, based upon maintenance_work_mem. There are three problems with that design

 - If the value of maintenance_work_mem is too large then it is a waste of memory for small tables.
 - If the value of maintenance_work_mem is too small or “TIDs” do not fit in the array then multiple scans happen.
 - In cases where maintainess_work_mem is set too large, and we have a bigger value of vacuume_count, then the system can be out-of-memory.

There are two solutions for these problems. The first is to use a list instead of a fixed size array.  The second solution is to allocate the memory in chunks.
The attached WIP patch creates an array of ItemPointers and allocates memory in chunks by dividing the maintenance_work_mem into multiple chunks.  

Comments?
--
Ibrar Ahmed
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