allocationSize50

allocationSize50 is a configuration parameter used in some ID generation schemes to control how many identifiers are allocated and cached in memory before requesting a new block from the database. The suffix 50 signifies a block size of fifty IDs.

In practice, allocationSize50 is most often encountered in object-relational mapping frameworks such as JPA or Hibernate, where a sequence or table-based generator is used to create primary keys. When the allocation size is set to 50, the generator retrieves a block of 50 IDs from the database and serves them from local memory. Once the in-memory block is exhausted, the generator requests the next block, and the process repeats.

How it works conceptually can be described using a hi/lo or pooled strategy. The generator obtains a high value (hi) from the database and then provides low values from 0 to 49 locally. The generated IDs are typically computed as hi multiplied by the allocation size plus the local offset. This approach minimizes round trips to the database, improving performance in high-throughput applications.

Pros of using a larger allocation size like 50 include reduced database load and better throughput, especially under concurrent access. Cons include the potential for gaps in ID sequences if the application shuts down or crashes mid-block, and a larger impact from any misconfiguration on cross-system ID generation. As a result, many configurations default to 50, balancing performance with predictability.

An example usage is configuring a sequence generator with allocationSize = 50, such as in a JPA annotation or XML mapping, to enable block preallocation of IDs.