Page History

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• Percent of dirty pages is trigger for checkpointing (e.g. 75%).
• Timeout is also trigger, do checkpoint every N seconds

CRC validation

For each page a control checksum (CRC32) is calculated. The CRC calculation is performed before each page is written to the page store. When a page is read from the page store, CRC is again calculated against the read data and validated against the CRC field also stored in the page.

If CRC validation fails, Ignite logs the failure and attempts to recover the page from WAL. If recovery succeeds, the node keeps running. If recovery fails, then node shuts down itself.

WAL

We can’t control moment when node crashes. Let's suppose we have saved tree leafs, but didn’t save tree root (during pages allocation they may be reordered because allocation is multithread). In this case all updates will be lost.

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