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Diffstat (limited to 'src/backend/utils/mmgr/README')
| -rw-r--r-- | src/backend/utils/mmgr/README | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/src/backend/utils/mmgr/README b/src/backend/utils/mmgr/README index 0ab81bd80ff..296fa198dc9 100644 --- a/src/backend/utils/mmgr/README +++ b/src/backend/utils/mmgr/README @@ -431,3 +431,26 @@ will not allocate very much space per tuple cycle. To make this usage pattern cheap, the first block allocated in a context is not given back to malloc() during reset, but just cleared. This avoids malloc thrashing. + + +Alternative Memory Context Implementations +------------------------------------------ + +aset.c is our default general-purpose implementation, working fine +in most situations. We also have two implementations optimized for +special use cases, providing either better performance or lower memory +usage compared to aset.c (or both). + +* slab.c (SlabContext) is designed for allocations of fixed-length + chunks, and does not allow allocations of chunks with different size. + +* generation.c (GenerationContext) is designed for cases when chunks + are allocated in groups with similar lifespan (generations), or + roughly in FIFO order. + +Both memory contexts aim to free memory back to the operating system +(unlike aset.c, which keeps the freed chunks in a freelist, and only +returns the memory when reset/deleted). + +These memory contexts were initially developed for ReorderBuffer, but +may be useful elsewhere as long as the allocation patterns match. |