GUC_LOG_CHUNK_SIZE
snapshot->num_chunks = DIV_ROUND_UP(snapshot->size, GUC_LOG_CHUNK_SIZE);
size_t size = min(GUC_LOG_CHUNK_SIZE, remain);
size_t size = min(GUC_LOG_CHUNK_SIZE, remain);
i * GUC_LOG_CHUNK_SIZE, size);
size_t size = min(GUC_LOG_CHUNK_SIZE, remain);
int chunk_from = from % GUC_LOG_CHUNK_SIZE;
int chunk_id = from / GUC_LOG_CHUNK_SIZE;
int to_chunk_id = to / GUC_LOG_CHUNK_SIZE;
int chunk_to = to % GUC_LOG_CHUNK_SIZE;
size_t size = (to_chunk_id == chunk_id ? chunk_to : GUC_LOG_CHUNK_SIZE) -
chunk_from = from % GUC_LOG_CHUNK_SIZE;
chunk_id = from / GUC_LOG_CHUNK_SIZE;