About Commit Protocols

The following table shows the durability and performance tradeoffs for the commit protocols when journaling is enabled. If you do not require durability and if you are concerned primarily about performance then you would typically specify the commit local option. While the commit safe option is the only setting that guarantees durability, the remote and region settings provide progressively more protection from data loss if there is a database process failure.

Values for the `commit` Database Option	Durability	Performance
`safe`	Guaranteed None	Fast Fastest
`region`
`remote`
`local`

For information on the commit database option, see Database Options.

Setting the Commit Protocol

You can use the commit database option to specify one of the following types of commit protocols for Transaction Engines (TEs):

safe
local
remote[:n]
region[:n]

Note: The default protocol is safe.

For each protocol, durability is a database transaction property that ensures that changes made during a transaction are persistent and can be re-created if a Storage Manager (SM) terminates and restarts. The following table describes each commit option argument. See also Choosing a Commit Protocol.

`safe`	TE sends a pre-commit message to each SM serving a modified storage group of the committing transaction. The TE then receives a pre-commit acknowledgment from each SM, and sends a commit confirmation message to the client. See About the Safe Commit Protocol.
`local`	TE sends a commit message to SM or SSM and does not wait for confirmation that the transaction was durably recorded.
`remote[:n]`	Note: A modified storage group is a storage group in which the transaction has inserted, deleted, or updated data serviced by that storage group. For each modified storage group, this option specifies the number of SMs or SSMs that must confirm the transaction was durably recorded before the TE reports the transaction as committed. The TE waits for the specified number of confirmations before sending a commit confirmation to the client. If the optional `:n` is not specified, then 1 SM or SSM per modified storage group is required to confirm that the transaction was durably recorded. If the optional `:n` is specified, then `n` SMs or SSMs per modified storage group are required to confirm durabilty. This implies a minimum number of SMs or SSMs in the domain. In this release, the `commit` protocol does not distinguish between SMs and SSMs.
`region[:n]`	For each modified storage group, this option specifies the number of regions that must confirm that the transaction was durably recorded before the TE reports the transaction as committed. In this release, the `commit` protocol does not distinguish between SMs and SSMs. If the optional `:n` suffix is specified, then for each modified storage group, the commit protocol requires an SM or SSM in `n` different regions to confirm that the transaction was durably recorded before the TE acknowledges that the transaction is committed. For a given storage group, SMs or SSMs that serve the group in the local region are preferred over SMs or SSMs that serve the group in remote regions. Consider the scenario in which there is one local region and two remote regions and `region:2` is specified. If a transaction modified a single storage group and at least one SM or SSM in the local region services that modified storage group then one of those SMs or SSMs must confirm that the transaction was durably recorded for that transaction to commit. Also, in one of the two remote regions, an SM or SSM that also services the modified storage group is required to confirm that the transaction was durably recorded. In the local region, if there are no SMs or SSMs that service the modified storage group, then an SM or SSM from each remote region must confirm that the transaction was durably recorded. It is possible for the local region to include SMs or SSMs that service some but not all of the modified storage groups. This means that SMs or SSMs in the local region can confirm that the transaction was durably recorded for only a subset of the modified storage groups. In this case: In the local region, only SMs or SSMs that service the modified storage groups are required to confirm that the transaction was durably recorded. In addition, a confirmation of durability must be received from an SM or SSM in `n-1` remote regions. Each modified storage group that is not serviced by SMs or SSMs in the local region requires an SM or SSM in `n` remote regions to confirm that the transaction was durably recorded. If the `:n` suffix is not specified, then `region:1` will be configured.