Expert Oracle Exadata - Parent Directory

CHAPTER 13 MIGRATING TO EXADATATable 13-4. Golden Gate Table CompressionMethod of Table LoadUncompressed Table (baseline) 3,443insert /*+ append */ select * from … 361GG direct load * 1,722GG direct load and ‘Append’ hint on the insert into the source table. 1,722Table Size (MB)* Note that Golden Gate has its own meaning for the term “direct load.” In Golden Gate terminology, itmeans that the initial table data copy (instantiation of a table) is done by directly inserting the extractedrows into the target database with array insert commands. The indirect approach in Golden Gate meansthat the initially extracted data is dumped to an extract file first and later loaded with other tools likeReplicat (initial-load mode) or Oracle’s SQL*Loader. This is why we didn’t see ideal compression withGolden Gate s “direct load” method as array inserts are not as good as INSERT SELECTs for compression.As for Streams, the documentation says that direct path inserts are not supported in 10g databases.11g does provide limited support through the Direct Path API. Once again, make sure you check theOracle documentation to see what is supported for your database version. If in doubt run a few tests tosee whether you do get the level of compression you expect. However, a big improvement in Oracle 11.2allows Streams to capture data from tables compressed with basic table compression and OLTPcompression. From Oracle 11.2.0.2 patchset onwards, Streams/XStream can also capture changes toHCC compressed tables. The Oracle Streams Concepts and Administration Guide for 11g Release 2 (11.2)explains this in more detail. This feature gives Streams a big advantage over Golden Gate if your sourcetables are compressed and the compressed data is updated, thus requiring some sort of change captureunless you want to copy all that data during downtime.The list of data types Streams does not support is fairly short in version 11gR2. Here is the list fromthe Oracle documentation:• BFILE• ROWID• User-defined types (including object types, REFs, varrays, and nested tables)• XMLType stored object relationally or as binary XML• The following Oracle-supplied types: Any types, URI types, spatial types, andmedia typesAnd here is the list of unsupported data types in Golden Gate:• BFILE• BLOB• CFILE445