What is the Error: WAL filled beyond 75% limit?

Rupert Harwood -

What does the error "WAL filled beyond 75% limit" mean when seen in the clustrix.log file?

Example:

2016-02-20 23:15:38.888734 UTC clustrix001.local.com clxnode: INFO storage/wal/wal_fs.c:339 wal_fs_get_write_permission(): WAL filled beyond 75% limit. Blocking appends until checkpoint completes, if behavior persists, try starting checkpoint early with -wal-fs-cp-start-pct”

The info message essentially means that the WAL is filling faster than it can be flushed to disk.

The WAL (write-ahead-log) is an in-memory write buffer in ClustrixDB. By default, the WAL begins flushing to disk once it reaches 50% full, and will begin blocking writes at 75% to ensure that system tasks responsible for flushing the WAL have enough headroom to complete. The resulting effect is some increased latency in these writes.

 

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