From: Jamison, Kirk [mailto:k.jami...@jp.fujitsu.com] > On the other hand, the simplest method I thought that could also work is > to only cache the file size (nblock) in shared memory, not in the backend > process, since both nblock and relsize_change_counter are uint32 data type > anyway. If relsize_change_counter can be changed without lock, then nblock > can be changed without lock, is it right? In that case, nblock can be accessed > directly in shared memory. In this case, is the relation size necessary > to be cached in backend?
Although I haven't looked deeply at Thomas's patch yet, there's currently no place to store the size per relation in shared memory. You have to wait for the global metacache that Ideriha-san is addressing. Then, you can store the relation size in the RelationData structure in relcache. > (2) Is the MdSharedData temporary or permanent in shared memory? > from the patch: > typedef struct MdSharedData > { > /* XXX could have an array of these, and use rel OID % nelements? > */ > pg_atomic_uint32 relsize_change_counter; > } MdSharedData; > > static MdSharedData *MdShared; Permanent in shared memory. Regards Takayuki Tsunakawa