=?UTF-8?B?5Zyf5Y2c55q/?= <pengcz(dot)nwpu(at)gmail(dot)com> writes:
> for studying polyphase merge algorithm of tuplesort.c, I use ddd and
> apend a table, which has a schema as follows:
> ...
> and has 36684 records, and every record is like:
> id code article name department
> 31800 266 \N Machault 77
> and for getting into external sort, I type the following command:
> select * from towns order by name desc;
> but I found it need not reach D5 and D6 during sorting,
That doesn't sound like enough data to force it to spill to disk at all;
at least not unless you turn down work_mem to some very small value.
regards, tom lane