This simplifies pipeProcessor initialization logic a bit.
This also doesn't mangle the original maxStateSize value, which is used in error messages when the state size exceeds maxStateSize.
Previously only logs inside the selected time range could be returned by stream_context pipe.
For example, the following query could return up to 10 surrounding logs only for the last 5 minutes,
while most users expect this query should return up to 10 surrounding logs without restrictions on the time range.
_time:5m panic | stream_context before 10
This enables the ability to implement stream context feature at VictoriaLogs web UI: https://github.com/VictoriaMetrics/VictoriaMetrics/issues/7063 .
Reduce memory usage when returning stream context over big log streams with millions of entries.
The new logic scans over all the log messages for the selected log stream, while keeping in memory only
the given number of surrounding logs. Previously all the logs for the given log stream on the selected time range
were loaded in memory before selecting the needed surrounding logs.
This should help https://github.com/VictoriaMetrics/VictoriaMetrics/issues/6730 .
Reduce the scan performance for big log streams by fetching only the requested fields. For example, the following
query should be executed much faster than before if logs contain many fields other than _stream, _msg and _time:
panic | stream_context after 30 | fields _stream, _msg, _time
The set of log fields in the found logs may differ from the set of log fields present in the log stream.
So compare only the log fields in the found logs when searching for the matching log entry in the log stream.
While at it, return _stream field in the delimiter log entry, since this field is used by VictoriaLogs Web UI
for grouping logs by log streams.
