Hi, Please see some responses below.
On Mon, Apr 7, 2025 at 9:13 PM Andres Freund <and...@anarazel.de> wrote: > Hi, > > On 2025-04-07 15:41:37 +0200, Daniel Gustafsson wrote: > > I think this function can be a valuable debugging aid going forward. > > What I am most excited about for this is to be able to measure server-wide > and > fleet-wide memory usage over time. Today I have actually very little idea > about what memory is being used for across all connections, not to speak > of a > larger number of servers. > > > > diff --git a/src/backend/postmaster/auxprocess.c > b/src/backend/postmaster/auxprocess.c > > index 4f6795f7265..d3b4df27935 100644 > > --- a/src/backend/postmaster/auxprocess.c > > +++ b/src/backend/postmaster/auxprocess.c > > @@ -84,6 +84,13 @@ AuxiliaryProcessMainCommon(void) > > /* register a before-shutdown callback for LWLock cleanup */ > > before_shmem_exit(ShutdownAuxiliaryProcess, 0); > > > > + /* > > + * The before shmem exit callback frees the DSA memory occupied by > the > > + * latest memory context statistics that could be published by > this aux > > + * proc if requested. > > + */ > > + before_shmem_exit(AtProcExit_memstats_dsa_free, 0); > > + > > SetProcessingMode(NormalProcessing); > > } > > How about putting it into BaseInit()? Or maybe just register it when its > first used? > > Problem with registering it when dsa is first used is that dsa is used in an interrupt handler. The handler could be called from the PG_ENSURE_ERROR_CLEANUP block. This block operates under the assumption that the before_shmem_exit callback registered at the beginning, will be the last one in the registered callback list at the end of the block. However, this won't be the case if a callback is registered from an interrupt handler called in the PG_ENSURE_ERROR_CLEANUP block. > I don't really understand why DSA_DEFAULT_INIT_SEGMENT_SIZE is something that makes sense to use here? > > To determine the memory limit per backend in multiples of DSA_DEFAULT_INIT_SEGMENT_SIZE. Currently it is set to 1 * DSA_DEFAULT_INIT_SEGMENT_SIZE. Since a call to dsa_create would create a DSA segment of this size, I thought it makes sense to define a limit related to the segment size. > > +/* > > + /* If the dsm mapping could not be found, attach to the area */ > > + if (dsm_seg != NULL) > > + return; > > I don't understand what we do here with the dsm? Why do we not need > cleanup > if we are already attached to the dsm segment? > I am not expecting to hit this case, since we are always detaching from the dsa. This could be an assert but since it is a cleanup code, I thought returning would be a harmless step. Thank you, Rahila Syed
