postgresql索引存的是oid和值么

存的是ctid, 以及索引字段的值。
ctid包含了blockID, itemID的信息，检索到块，从而检索到块的linepoint，linepoint记录了行在块内的OFFSET，最终检索到行。

用pageinspect可以观察到。
例如：

postgres=# select * fro m bt_page_items('idx_t',100);
 itemoffset |   ctid    | itemlen | nulls | vars |          data           
------------+-----------+---------+-------+------+-------------------------
          1 | (160,75)  |      16 | f     | f    | 8b 8d 00 00 00 00 00 00
          2 | (158,161) |      16 | f     | f    | 1d 8c 00 00 00 00 00 00
          3 | (158,162) |      16 | f     | f    | 1e 8c 00 00 00 00 00 00
          4 | (158,163) |      16 | f     | f    | 1f 8c 00 00 00 00 00 00
          5 | (158,164) |      16 | f     | f    | 20 8c 00 00 00 00 00 00
          6 | (158,165) |      16 | f     | f    | 21 8c 00 00 00 00 00 00
          7 | (158,166) |      16 | f     | f    | 22 8c 00 00 00 00 00 00
          8 | (158,167) |      16 | f     | f    | 23 8c 00 00 00 00 00 00
          9 | (158,168) |      16 | f     | f    | 24 8c 00 00 00 00 00 00
         10 | (158,169) |      16 | f     | f    | 25 8c 00 00 00 00 00 00
         11 | (158,170) |      16 | f     | f    | 26 8c 00 00 00 00 00 00
         12 | (158,171) |      16 | f     | f    | 27 8c 00 00 00 00 00 00
         13 | (158,172) |      16 | f     | f    | 28 8c 00 00 00 00 00 00
         14 | (158,173) |      16 | f     | f    | 29 8c 00 00 00 00 00 00