Informix Error -186: ISAM error: Cannot open partition. Online create/drop index in progress.

Reasons / Common Causes

-186 is a brief, expected, transient condition — similar in spirit to -106 and -113 — that occurs when something tries to open a partition while an online CREATE INDEX or DROP INDEX operation is running against it. Online index operations are designed to minimize disruption, but there's still a brief window where certain access needs to wait.

1. An online CREATE INDEX or DROP INDEX operation currently in progress against the table or partition, briefly restricting other operations from opening it.
2. An application or query accessing the table at exactly the moment an online index build/drop is running — most access continues normally during an online operation, but a specific access pattern still needs exclusive partition access briefly.
3. A schema-maintenance job running index builds during active business hours, without awareness that specific access patterns can briefly trigger -186 even though the operation is designed to be "online."

Solutions / Resolution

1. Wait a short time and retry, per the official guidance — this is normally very brief and self-resolving.
2. Build retry-with-backoff logic into applications for this specific condition, the same general pattern as for -106/-107.
3. If this becomes disruptive, consider scheduling online index create/drop operations during lower-traffic windows, even though they're designed to minimize disruption generally.
4. Monitor frequency if this recurs often enough to be an operational annoyance, to decide whether index-maintenance scheduling needs adjustment.

Examples

The expected transient wait

-- Session A: an online index build running against orders
CREATE INDEX orders_status_idx ON orders (status) ONLINE;

-- Session B, briefly during the build:
SELECT * FROM orders WHERE id = 1;
-- -186: wait briefly and retry

Retrying moments later succeeds without any other change — the online index operation completing (or reaching a point where this specific access pattern is no longer restricted) resolves it.

Retry logic

while (iserrno == -186) {
    sleep(1);
    retry_operation();
}

Diagnostic Checks

1. Check for an active online index create/drop operation against the affected table:

   onstat -g ddl
   

2. Correlate the timing with any scheduled index-maintenance jobs, if this recurs unexpectedly.

Related Errors / Related Topics

• -106 — "ISAM error: non-exclusive access." The general exclusivity-conflict family this belongs to.
• -113 — "ISAM error: the file is locked." Another transient access-conflict condition with the same "wait and retry" resolution shape.

Wait and retry first — this is normally brief and self-resolving, not something requiring investigation unless it recurs persistently against the same table.