influxd-ctl truncate-shards

The influxd-ctl truncate-shards command truncates all shards that are currently being written to (also known as “hot” shards) and creates new shards to write new data to.

Usage

influxd-ctl truncate-shards [flags]

Flags

Examples

Truncate shards 3 minutes after command execution

influxd-ctl truncate-shards -delay 3m

Understand the risks with future data

When you write data points with timestamps in the future (for example, forecast data from machine learning models), the truncate-shards command behaves differently and can cause data duplication issues.

How truncate-shards normally works

For shards containing current data:

1. The command creates an artificial stop point in the shard at the truncation timestamp
2. Creates a new shard starting from the truncation point
3. Example: A one-week shard (Sunday to Saturday) becomes:
   • Shard A: Sunday to truncation point (Wednesday 2pm)
   • Shard B: Truncation point (Wednesday 2pm) to Saturday

This works correctly because the meta nodes understand the boundaries and route queries appropriately.

The problem with future data

For shards containing future timestamps:

1. The truncation doesn’t cleanly split the shard at a point in time
2. Instead, it creates overlapping shards that cover the same time period
3. Example: If you’re writing September forecast data in August:
   • Original shard: September 1-7
   • After truncation:
     • Shard A: September 1-7 (with data up to truncation)
     • Shard B: September 1-7 (for new data after truncation)
   • Result: Duplicate data points for the same timestamps