This is the existing WAL + cache implementation. Moving it to a separate file
so that it can remain intact while a refactoring to a independent WAL can occur.
The WAL was also named Log in the code so this names file more closely to the concept
in the code.
Mainly for debugging as since this should not happen going forward. Since
there may be points with NaN already stored in the WAL, this is helpful for
troubleshooting panics.
When a database is dropped, removing old segments returns an error
because the files are already gone. Using RemoveAll handles this
case more gracefully.
If a drop database is executed while writes are in flight, a panic
could occur because the WAL would fail to write to the DB dirs where
had been removed.
Partil fix for #4538
Close acquired the cacheLock and writeLock in a different order than flush. If addToCache was also
running in a goroutine (acquiring cacheLock), a deadlock could happen.
panic: error opening new segment file for wal: open /var/folders/lj/vlbynqp52pxdxxlxx64j6bk80000gn/T/tsm1-test709000715/_00002.wal: no such file or directory
goroutine 8 [running]:
github.com/influxdb/influxdb/tsdb/engine/tsm1.(*Log).writeToLog(0xc820098500, 0x1, 0xc8201584b0, 0x1c, 0x45, 0x0, 0x0)
/Users/jason/go/src/github.com/influxdb/influxdb/tsdb/engine/tsm1/wal.go:427 +0xc19
Jason Wilder
Ben Johnson
Paul Dix