Permit super-MaxAllocSize allocations with MemoryContextAllocHuge().

The MaxAllocSize guard is convenient for most callers, because it
reduces the need for careful attention to overflow, data type selection,
and the SET_VARSIZE() limit.  A handful of callers are happy to navigate
those hazards in exchange for the ability to allocate a larger chunk.
Introduce MemoryContextAllocHuge() and repalloc_huge().  Use this in
tuplesort.c and tuplestore.c, enabling internal sorts of up to INT_MAX
tuples, a factor-of-48 increase.  In particular, B-tree index builds can
now benefit from much-larger maintenance_work_mem settings.

Reviewed by Stephen Frost, Simon Riggs and Jeff Janes.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/include/utils/palloc.h b/src/include/utils/palloc.h
index 420bde7ee4a..01e7db5d4f9 100644
--- a/src/include/utils/palloc.h
+++ b/src/include/utils/palloc.h
@@ -51,6 +51,10 @@ extern void *MemoryContextAlloc(MemoryContext context, Size size);
 extern void *MemoryContextAllocZero(MemoryContext context, Size size);
 extern void *MemoryContextAllocZeroAligned(MemoryContext context, Size size);
 
+/* Higher-limit allocators. */
+extern void *MemoryContextAllocHuge(MemoryContext context, Size size);
+extern void *repalloc_huge(void *pointer, Size size);
+
 /*
  * The result of palloc() is always word-aligned, so we can skip testing
  * alignment of the pointer when deciding which MemSet variant to use.