NonStop SQL DDL Replicator User's Guide (Update 7)

SDR Operations
HP NonStop SQL DDL Replicator User’s Guide—545799-007
4-7
DDL Replication
See paragraph Handling DDL Operations performed under a User Transactions on
page 3-4 for a discussion on the options available to deal with this situation.
Distributed Tables and Indexes
If a table or index is distributed, with partitions or indexes on multiple systems, RDF
updaters on all systems must be stopped at the same point in processing their primary
system audit. SDR writes SRU audit to the audit trail of every referenced system.
Since SDR might be processing another distributed DDL operation at the same time,
this leads to the possibility of confusion and deadlock. Two sequences of SRU audit
records sent to remote audit trails might be inserted in different orders. One RDF might
be waiting for one distributed DDL replication while another RDF is waiting for a
different DDL replication.
To avoid this problem, SDR obtains an SDR lock on each of the affected systems
before writing any of the SRU audit. The SDR monitor on each system manages the
lock. If SDR cannot immediately obtain all the locks it needs, it releases all the locks,
waits for a short time, and tries again. A random backoff algorithm ensures resolution
within a short time.
If the SDR monitor on any of the affected systems is not accessible, the DDL operation
will be terminated with an error message.
Unaudited Tables and Indexes
SDR writes every DDL operation to a depot file, but it writes the SRU audit record only
if the target SQL object is audited. Since the SRU audit initiates SDR replication, DDL
for unaudited objects is not replicated. See Replicating Unaudited Tables on page 3-7
for options available to process DDL replication on unaudited tables.
SQLCI DUP Utility
The DUP command executes several internal DDL operations to create tables and
indexes and to alter table attributes. DDL for DUP operations are never captured or
replicated by SDR.
DDL Replication
The following paragraphs discuss topics relating to the replication of the captured DDL
statements to the backup system(s):
SDR Updater Processes
Replication Operations
Note. If you have a serious need to execute DDL in a user transaction, please contact HP
product support.