Description

When changing the shard for a chain using graphman chain change-shard, the existing chain is correctly renamed to <chain>-old and persists in the database.

However, if a subsequent attempt is made to revert the chain's shard back to the original shard (which would cause the currently active chain to be renamed to <chain>-old again), the operation fails due to a unique constraint violation on the chains table. The error indicates that the key value (<chain>-old) already exists, as it was created during the initial shard change.

Steps to Reproduce

• Start with chain A on shard S1 (e.g., matic on polygon_chain).
• Change the shard for chain A to S2 (e.g., primary):

graphman chain change-shard A S2
# Result: Successful. A is on S2. A-old (the original chain) is on S1.

• Attempt to change the shard for chain A back to the original shard S1:

graphman chain change-shard A S1

Expected Behavior

The shard change should complete successfully. The current chain A (on S2) should be renamed to A-old (or a more uniquely named backup), and the old chain A-old (on S1) should be re-promoted/renamed to A.

Actual Behavior

The command fails with a database constraint violation:

Error: database constraint violated: duplicate key value violates unique constraint "chains_name_key": Key (name)=(matic-old) already exists.

Additional

The current logic for change-shard unconditionally attempts to rename the current chain to <chain>-old. This approach is fragile because it doesn't account for the persistence of a previously archived <chain>-old entity. The failure occurs because the database enforces a unique constraint on the name column.

Relevant log output

root@b5c46359fc62:/# graphman chain change-shard matic primary
Changing block cache shard for matic to primary
Current shard: polygon_chain
Error: database constraint violated: duplicate key value violates unique constraint "chains_name_key": Key (name)=(matic-old) already exists.

IPFS hash

No response

Subgraph name or link to explorer

No response

Some information to help us out

• Tick this box if this bug is caused by a regression found in the latest release.
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OS information

Linux