I'm trying to wrap my head around the shared memory stats collector infrastructure from <20220406030008.2qxipjxo776dw...@alap3.anarazel.de> committed in 5891c7a8ed8f2d3d577e7eea34dacff12d7b6bbd.
I have one question about locking -- afaics there's nothing protecting reading the shared memory stats. There is an lwlock protecting concurrent updates of the shared memory stats, but that lock isn't taken when we read the stats. Are we ok relying on atomic 64-bit reads or is there something else going on that I'm missing? In particular I'm looking at pgstat.c:847 in pgstat_fetch_entry() which does this: memcpy(stats_data, pgstat_get_entry_data(kind, entry_ref->shared_stats), kind_info->shared_data_len); stats_data is the returned copy of the stats entry with all the statistics in it. But it's copied from the shared memory location directly using memcpy and there's no locking or change counter or anything protecting this memcpy that I can see. -- greg
