High Availability Options for Db2 LUW

Why Should a Database be Highly Available?

It is significantly easier to implement high availability at other levels than it is at the database level. Often the database server is one of the more powerful servers in an environment, and without some fancy footwork there can be only one live copy of data. Ignoring high availability at the database level due to expense can be a bankruptcy-inducing choice for an organization. Just imagine what would happen if your databases suddenly did not exist. Not only would your company be unable to perform daily business, but the data lost could actually drive a company out of business.

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Comparing Two Db2 Systems

Sometimes configuration needs to be kept in sync between two or more Db2 systems. There are a variety of reasons – sometimes this is for keeping two HADR servers in sync, and other times it may be for keeping a dev, QA, or Staging system in sync with production. In any case, having an idea of what needs to be in sync and what doesn’t can be complicated. The focus here is at the system level. This post does not dig into comparison of logical objects in the database such as tables and indexes.

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DB2 Temporary Table Spaces

What is Temp Space in Db2?

Db2 needs some temporary space on disk to perform some actions. Commonly we think of these actions as primarily sort and join operations. These are operations where Db2 will first use the SORTHEAP memory area, but some data sets are just too big to fit in these locations. Even when an operation spills to temporary space, it may technically still occur in memory – just in the buffer pool for the temporary tablespace. Any type of data manipulation may require these sorts of operations. Db2 uses a system temporary table space for this kind of spill. There is also another type of temporary table space called a user temporary table space

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A Physical DBA Reviewing DDL

My background comes largely from the physical DBA world, though I’ve gained logical DBA skills over the years. Any reasonably mature IT organization will have a DBA at some level or another review SQL and DDL before it is implemented in production.

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Calculating Row Width and Choosing a Page Size in DB2

A DB2 DBA must be able to calculate the row width. The row width can be used to estimate table size, and also to pick a tablespace with the correct page size. DB2 is more strict about a row fitting on a page. For general purposes, a DB2 table must be in a tablespace where any row, minus LOBs fits on a single page. There is an option for extended row size. This feature, in my head, is only there for Oracle compatibility, and should not be used when there are other choices.

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Going Beyond 2 Servers – HADR as a High Availability/Disaster Recovery option.

When the client considers high availability and disaster recovery, they often do not know what they are talking about. Many times the client may be dropping buzzwords like “five nines”. To them this is the definition of disaster recovery. In other cases, they are thinking of a worst-case scenario where a whole data center falls off the face of the earth and they need high availability.

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