Golengate的基本工作原理是通过挖掘重做日志以获取数据库中的数据变化；而如果我们在数据库中使用并行DML去插入数据的话会因为直接路径插入而产生少量的redo重做日志。那么OGG的日志挖掘是否能正确捕获这些并行DML所产生的数据变化呢？接着我们来实际地测试一下:

SQL> select le.leseq "Current log sequence No",2         100 * cp.cpodr_bno / le.lesiz "Percent Full",3         (cpodr_bno - 1) * 512 "Current Offset",4         le.lesiz * 512 - cpodr_bno * 512 "Left space"5    from x$kcccp cp, x$kccle le6   where LE.leseq = CP.cpodr_seq7     and bitand(le.leflg, 24) = 8;Current log sequence No Percent Full Current Offset Left space
----------------------- ------------ -------------- ----------177   78.5112305       82324480   22532608/* 通过以上查询我们可以了解实际的redo写出情况:Current Offset说明了当前日志文件所写到的位置，而Left Space说明了当前日志文件所剩余的空间
82324480(Current Offset)+22532608(Left space)+512(redo header)=logfile size=le.lesiz* redo block size
*/SQL> alter system switch logfile;
System altered.SQL> select le.leseq "Current log sequence No",2         100 * cp.cpodr_bno / le.lesiz "Percent Full",3         (cpodr_bno - 1) * 512 "Current Offset",4         le.lesiz * 512 - cpodr_bno * 512 "Left space"5    from x$kcccp cp, x$kccle le6   where LE.leseq = CP.cpodr_seq7     and bitand(le.leflg, 24) = 8;Current log sequence No Percent Full Current Offset Left space
----------------------- ------------ -------------- ----------179   .002441406           2048  104855040/* 初始位置为No 179的日志文件 */SQL> select le.leseq "Current log sequence No",2         100 * cp.cpodr_bno / le.lesiz "Percent Full",3         (cpodr_bno - 1) * 512 "Current Offset",4         le.lesiz * 512 - cpodr_bno * 512 "Left space"5    from x$kcccp cp, x$kccle le6   where LE.leseq = CP.cpodr_seq7     and bitand(le.leflg, 24) = 8;Current log sequence No Percent Full Current Offset Left space
----------------------- ------------ -------------- ----------180    58.277832       61108224   43748864/* 使用普通非并行DML插入产生了104855040+61108224=158M的redo */SQL> truncate table tv;
Table truncated.SQL> select le.leseq "Current log sequence No",2         100 * cp.cpodr_bno / le.lesiz "Percent Full",3         (cpodr_bno - 1) * 512 "Current Offset",4         le.lesiz * 512 - cpodr_bno * 512 "Left space"5    from x$kcccp cp, x$kccle le6   where LE.leseq = CP.cpodr_seq7     and bitand(le.leflg, 24) = 8;Current log sequence No Percent Full Current Offset Left space
----------------------- ------------ -------------- ----------180   60.6469727       63592448   41264640/* 初始为No 180日志文件的63592448 */SQL> alter session enable parallel dml;
Session altered./* 在session级别启用并行DML */SQL> set autotrace on;
SQL> insert /*+ parallel(tv,4) */ into tv select * from sample;3640772 rows created.
Execution Plan
----------------------------------------------------------
ERROR:
ORA-12838: cannot read/modify an object after modifying it in parallel
SP2-0612: Error generating AUTOTRACE EXPLAIN report
Statistics
----------------------------------------------------------111  recursive calls1168  db block gets17850  consistent gets17745  physical reads97944  redo size815  bytes sent via SQL*Net to client750  bytes received via SQL*Net from client3  SQL*Net roundtrips to/from client1  sorts (memory)0  sorts (disk)3640772  rows processed/* autotrace statistics显示并行插入仅产生了97944字节的redo */SQL> commit;
Commit complete.SQL> select le.leseq "Current log sequence No",2         100 * cp.cpodr_bno / le.lesiz "Percent Full",3         (cpodr_bno - 1) * 512 "Current Offset",4         le.lesiz * 512 - cpodr_bno * 512 "Left space"5    from x$kcccp cp, x$kccle le6   where LE.leseq = CP.cpodr_seq7     and bitand(le.leflg, 24) = 8;Current log sequence No Percent Full Current Offset Left space
----------------------- ------------ -------------- ----------182   10.4882813       10997248   93859840/* 而实际上日志由180切换到了182，实际的redo产生大约是41264640+104857600+10997248=150M *//* 换而言之autotrace对并行DML语句所产生的实际redo统计远少于实际值，这也就保证了extract能够捕获到所有这些并行DML所引起的数据变化
*/GGSCI (rh2.oracle.com) 59> stats load2
Sending STATS request to EXTRACT LOAD2 ...Start of Statistics at 2010-12-16 20:17:35.Output to /s01/new/ze:Extracting from CLINIC.TV to CLINIC.TV:*** Total statistics since 2010-12-16 20:17:24 ***Total inserts                           923555.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        923555.00*** Daily statistics since 2010-12-16 20:17:24 ***Total inserts                           923555.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        923555.00*** Hourly statistics since 2010-12-16 20:17:24 ***Total inserts                           923555.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        923555.00*** Latest statistics since 2010-12-16 20:17:24 ***Total inserts                           923555.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        923555.00End of Statistics.GGSCI (rh2.oracle.com) 60> !
stats load2Sending STATS request to EXTRACT LOAD2 ...Start of Statistics at 2010-12-16 20:17:37.Output to /s01/new/ze:Extracting from CLINIC.TV to CLINIC.TV:*** Total statistics since 2010-12-16 20:17:24 ***Total inserts                           1090336.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1090336.00*** Daily statistics since 2010-12-16 20:17:24 ***Total inserts                           1090336.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1090336.00*** Hourly statistics since 2010-12-16 20:17:24 ***Total inserts                           1090336.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1090336.00*** Latest statistics since 2010-12-16 20:17:24 ***Total inserts                           1090336.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1090336.00End of Statistics.GGSCI (rh2.oracle.com) 61> !
stats load2Sending STATS request to EXTRACT LOAD2 ...Start of Statistics at 2010-12-16 20:17:39.Output to /s01/new/ze:Extracting from CLINIC.TV to CLINIC.TV:*** Total statistics since 2010-12-16 20:17:24 ***Total inserts                           1249284.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1249284.00*** Daily statistics since 2010-12-16 20:17:24 ***Total inserts                           1249284.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1249284.00*** Hourly statistics since 2010-12-16 20:17:24 ***Total inserts                           1249284.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1249284.00*** Latest statistics since 2010-12-16 20:17:24 ***Total inserts                           1249284.00Total updates                                0.00Total deletes                                0.00Total discards                               0.00Total operations                        1249284.00End of Statistics./* 可以看到extract的统计信息中Total inserts不断递增，说明extract正确捕获了所有由并行INSERT引发的直接路径插入操作
*/

Does Oracle Goldengate support Parallel DML? 结论显然是: Yes。