Comparing time series data is crucial for identifying trends, anomalies, and patterns over time. In Splunk, visualizing this comparison effectively can provide valuable insights. This article explores practical techniques to compare time series data using Splunk’s charting capabilities, focusing on methods to highlight differences and similarities across various time ranges.
One effective approach involves using the eval command in conjunction with timechart to overlay different time periods on the same graph. This allows for a direct visual comparison. For instance, to compare today’s data with yesterday’s data, you can use the relative_time function within eval to create distinct categories.
```splunk
<your search query>
| eval marker = if (_time < relative_time(now(), "@d"), "yesterday", "today")
| eval _time = if (marker=="yesterday", _time+24*60*60, _time)
| timechart sum(volume) by marker
This search query first categorizes events into "yesterday" and "today" based on their timestamps using `relative_time(now(), "@d")`, which represents the beginning of the current day. Then, for events marked "yesterday", the timestamp (`_time`) is shifted forward by 24 hours, effectively aligning yesterday's data with today's timeline for charting purposes. Finally, `timechart` visualizes the sum of 'volume' for each category ('yesterday' and 'today') over time, allowing for a direct comparison on a single chart. This method is particularly useful for day-over-day performance analysis.
Alternatively, if you aim to compare data across different categories, such as hosts, instead of time, you can adapt the same `eval` technique and utilize the `chart` command. Instead of `timechart`, `chart` allows for creating categorical charts.
```markdown
```splunk
<your search query>
| eval marker = if (_time < relative_time(now(), "@d"), "yesterday", "today")
| eval _time = if (marker=="yesterday", _time+24*60*60, _time)
| chart sum(volume) over host by marker
In this variation, the query remains similar in its use of `eval` to categorize and time-shift data. However, `chart sum(volume) over host by marker` generates a chart where the x-axis represents 'host' values, and the data is segmented by the 'marker' field ("yesterday" and "today"). This allows for comparing the 'volume' across different hosts for both time periods side-by-side.
For scenarios requiring comparison of data over different time spans or non-contiguous periods, Splunk offers efficient methods using `bin` and `convert`. The `bin` command groups events into time intervals, and `convert` can format the `_time` field for clearer presentation on charts.
```markdown
```splunk
<your search query>
| bin _time span=1h
| convert ctime(_time) timeformat="%m/%d"
| chart sum(volume) by _time
Here, `bin _time span=1h` groups events into 1-hour intervals. `convert ctime(_time) timeformat="%m/%d"` formats the `_time` field to display only month and day, simplifying the x-axis labels. Finally, `chart sum(volume) by _time` creates a time-based chart showing the sum of 'volume' for each binned time interval. This approach is beneficial for visualizing trends and patterns across aggregated time segments.
In conclusion, Splunk provides versatile tools for visualizing and comparing time series data. Whether you need to compare data from yesterday and today, analyze categorical breakdowns across time periods, or examine trends over aggregated time intervals, Splunk's `timechart`, `chart`, `eval`, `bin`, and `convert` commands offer powerful solutions for effective data comparison and analysis.
**References:**
* [Splunk `eval` function documentation](http://www.splunk.com/base/Documentation/latest/SearchReference/CommonEvalFunctions)
* [Splunk Answers: Getting result like timechart but with reversed axes](http://answers.splunk.com/questions/1286/is-there-a-way-to-get-a-result-that-looks-like-timechart-but-with-the-axes-rever)
* [Splunk Answers: Table of statistics with different columns for different times](http://answers.splunk.com/questions/1288/can-i-get-a-table-of-statistics-where-different-columns-represent-different-time)