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david-rowleydavid-rowley
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Introduce a bump memory allocator
This introduces a bump MemoryContext type. The bump context is best suited for short-lived memory contexts which require only allocations of memory and never a pfree or repalloc, which are unsupported. Memory palloc'd into a bump context has no chunk header. This makes bump a useful context type when lots of small allocations need to be done without any need to pfree those allocations. Allocation sizes are rounded up to the next MAXALIGN boundary, so with this and no chunk header, allocations are very compact indeed. Allocations are also very fast as bump does not check any freelists to try and make use of previously free'd chunks. It just checks if there is enough room on the current block, and if so it bumps the freeptr beyond this chunk and returns the value that the freeptr was previously pointing to. Simple and fast. A new block is malloc'd when there's not enough space in the current block. Code using the bump allocator must take care never to call any functions which could try to call realloc() (or variants), pfree(), GetMemoryChunkContext() or GetMemoryChunkSpace() on a bump allocated chunk. Due to lack of chunk headers, these operations are unsupported. To increase the chances of catching such issues, when compiled with MEMORY_CONTEXT_CHECKING, bump allocated chunks are given a header and any attempt to perform an unsupported operation will result in an ERROR. Without MEMORY_CONTEXT_CHECKING, code attempting an unsupported operation could result in a segfault. A follow-on commit will implement the first user of bump. Author: David Rowley Reviewed-by: Nathan Bossart Reviewed-by: Matthias van de Meent Reviewed-by: Tomas Vondra Reviewed-by: John Naylor Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com
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‎src/backend/nodes/gen_node_support.pl

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# they otherwise don't participate in node support.
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my @extra_tags = qw(
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IntList OidList XidList
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AllocSetContext GenerationContext SlabContext
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AllocSetContext GenerationContext SlabContext BumpContext
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TIDBitmap
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WindowObjectData
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);

‎src/backend/utils/mmgr/Makefile

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OBJS = \
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alignedalloc.o \
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aset.o \
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bump.o \
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dsa.o \
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freepage.o \
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generation.o \

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