5.2 Configuration Read Phase (STTOR Phase -1)

The READ_CONFIG_REQ signal provides all kernel blocks an opportunity to read the configuration data, which is stored in a global object accessible to all blocks. All memory allocation in the data nodes takes place during this phase.

Note

Connections between the kernel blocks and the NDB file system are also set up during Phase 0. This is necessary to enable the blocks to communicate easily which parts of a table structure are to be written to disk.

NDB performs memory allocations in two different ways. The first of these is by using the allocRecord() method (defined in storage/ndb/src/kernel/vm/SimulatedBlock.hpp). This is the traditional method whereby records are accessed using the ptrCheckGuard macros (defined in storage/ndb/src/kernel/vm/pc.hpp). The other method is to allocate memory using the setSize() method defined with the help of the template found in storage/ndb/src/kernel/vm/CArray.hpp.

These methods sometimes also initialize the memory, ensuring that both memory allocation and initialization are done with watchdog protection.

Many blocks also perform block-specific initialization, which often entails building linked lists or doubly-linked lists (and in some cases hash tables).

Many of the sizes used in allocation are calculated in the Configuration::calcSizeAlt() method, found in storage/ndb/src/kernel/vm/Configuration.cpp.

Some preparations for more intelligent pooling of memory resources have been made. DataMemory and disk records already belong to this global memory pool.