What is SQL Server internal logging buffer and log flush mechanism?

SQL Server batches log records in memory and flushes them to disk on commit or flush triggers.

Transaction log records are first written to an in-memory log buffer. On commit, SQL Server ensures durability by flushing the log buffer to disk (WRITE-AHEAD LOGGING). Multiple transactions can share a single flush operation (group commit), improving performance. Flushes can be triggered by checkpoints, log buffer thresholds, or explicit commits.