On Fri, Dec 2, 2016 at 9:36 AM, Robert Haas <rh...@postgresql.org> wrote:
> Introduce dynamic shared memory areas.
> Programmers discovered decades ago that it was useful to have a simple
> interface for allocating and freeing memory, which is why malloc() and
> free() were invented.  Unfortunately, those handy tools don't work
> with dynamic shared memory segments because those are specific to
> PostgreSQL and are not necessarily mapped at the same address in every
> cooperating process.  So invent our own allocator instead.  This makes
> it possible for processes cooperating as part of parallel query
> execution to allocate and free chunks of memory without having to
> reserve them prior to the start of execution.  It could also be used
> for longer lived objects; for example, we could consider storing data
> for pg_stat_statements or the stats collector in shared memory using
> these interfaces, rather than writing them to files.  Basically,
> anything that needs shared memory but can't predict in advance how
> much it's going to need might find this useful.
> Thomas Munro and Robert Haas.  The original code (of mine) on which
> Thomas based his work was actually designed to be a new backend-local
> memory allocator for PostgreSQL, but that hasn't gone anywhere - or
> not yet, anyway.  Thomas took that work and performed major
> refactoring and extensive modifications to make it work with dynamic
> shared memory, including the addition of appropriate locking.

This commit is generating a warning when compiling on my Win7 dev box:
"C:\Users\ioltas\git\postgres\pgsql.sln" (default target) (1) ->
"C:\Users\ioltas\git\postgres\postgres.vcxproj" (default target) (2) ->
(ClCompile target) ->
  src/backend/utils/mmgr/dsa.c(1921): warning C4334: '<<' : result of 32-bit sh
ift implicitly converted to 64 bits (was 64-bit shift intended?) [C:\Users\iolt

    1 Warning(s)
    0 Error(s)

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