恢复用户表和用户历史表名称

已通过enable_recyclebin参数和recyclebin_retention_time参数开启闪回DROP功能，恢复用户表和用户历史表名称。示例如下：

• DROP用户表，对用户表执行闪回DROP。使用ledger_hist_repair对用户表、用户历史表进行表名恢复。

  -- 对用户表执行闪回drop，使用ledger_hist_repair对用户历史表进行表名恢复。
  gaussdb=# CREATE TABLE ledgernsp.tab2(a int, b text);
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'a' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'rec_num' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  CREATE TABLE
  gaussdb=# DROP TABLE ledgernsp.tab2;
  DROP TABLE
  gaussdb=# SELECT rcyrelid, rcyname, rcyoriginname FROM gs_recyclebin;
   rcyrelid |           rcyname            |    rcyoriginname
  ----------+------------------------------+---------------------
      32838 | BIN$39B523388046$55C8400==$0 | tab2
      32846 | BIN$39B52338804E$55C90E8==$0 | gs_hist_tab2_index
      32843 | BIN$39B52338804B$55C96A0==$0 | ledgernsp_tab2_hist
      32841 | BIN$39B523388049$55C9EE0==$0 | pg_toast_32838
  (4 rows)
  -- 对用户表执行闪回drop。
  gaussdb=# TIMECAPSULE TABLE ledgernsp.tab2 TO BEFORE DROP;
  TimeCapsule Table
  -- 使用ledger_hist_repair恢复用户历史表表名。
  gaussdb=# SELECT ledger_hist_repair('ledgernsp', 'tab2');
   ledger_hist_repair
  --------------------
   0000000000000000
  (1 row)
  
  gaussdb=# \d+ ledgernsp.tab2;
                            Table "ledgernsp.tab2"
     Column    |  Type   | Modifiers | Storage  | Stats target | Description
  -------------+---------+-----------+----------+--------------+-------------
   a           | integer |           | plain    |              |
   b           | text    |           | extended |              |
   hash_1d2d14 | hash16  |           | plain    |              |
  Has OIDs: no
  Distribute By: HASH(a)
  Location Nodes: ALL DATANODES
  Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=enhanced_toast
  History table name: ledgernsp_tab2_hist
  
  -- 对用户表执行闪回drop，使用ledger_hist_repair对用户表进行表名恢复。
  gaussdb=# CREATE TABLE ledgernsp.tab3(a int, b text);
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'a' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  NOTICE:  The 'DISTRIBUTE BY' clause is not specified. Using 'rec_num' as the distribution column by default.
  HINT:  Please use 'DISTRIBUTE BY' clause to specify suitable data distribution column.
  CREATE TABLE
  gaussdb=# DROP TABLE ledgernsp.tab3;
  DROP TABLE
  gaussdb=# SELECT rcyrelid, rcyname, rcyoriginname FROM gs_recyclebin;
   rcyrelid |           rcyname            |    rcyoriginname
  ----------+------------------------------+---------------------
      32952 | BIN$80B6233880B8$FECFF98==$0 | tab3
      32960 | BIN$80B6233880C0$FED0C98==$0 | gs_hist_tab3_index
      32957 | BIN$80B6233880BD$FED1250==$0 | ledgernsp_tab3_hist
      32955 | BIN$80B6233880BB$FED1A00==$0 | pg_toast_32952
  (4 rows)
  -- 对用户历史表执行闪回drop。
  gaussdb=# TIMECAPSULE TABLE blockchain.ledgernsp_tab3_hist TO BEFORE DROP;
  TimeCapsule Table
  -- 拿到回收站中用户表对应的rcyname，使用ledger_hist_repair恢复用户表表名。
  gaussdb=# SELECT ledger_hist_repair('ledgernsp', 'BIN$80B6233880B8$FECFF98==$0');
   ledger_hist_repair
  --------------------
   0000000000000000
  (1 row)
  
  gaussdb=# \d+ ledgernsp.tab3;
                            Table "ledgernsp.tab3"
     Column    |  Type   | Modifiers | Storage  | Stats target | Description
  -------------+---------+-----------+----------+--------------+-------------
   a           | integer |           | plain    |              |
   b           | text    |           | extended |              |
   hash_7a0c87 | hash16  |           | plain    |              |
  Has OIDs: no
  Distribute By: HASH(a)
  Location Nodes: ALL DATANODES
  Options: orientation=row, compression=no, storage_type=USTORE, segment=off, toast.storage_type=USTORE, toast.toast_storage_type=enhanced_toast
  History table name: ledgernsp_tab3_hist
  
  -- 删除表。
  gaussdb=# DROP TABLE ledgernsp.tab2 PURGE;
  DROP TABLE
  gaussdb=# DROP TABLE ledgernsp.tab3 PURGE;
  DROP TABLE