Opster Team
Before you begin reading this guide, we recommend you run Elasticsearch Error Check-Up which analyzes 2 JSON files to detect many errors.
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This guide will help you check for common problems that cause the log ” Failed to notify callback ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: indices.

Log Context
Log “failed to notify callback” classname is AsyncIOProcessor.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
for (Tuple- > tuple : candidates) { Consumer
consumer = tuple.v2(); try { consumer.accept(exception); } catch (Exception ex) { logger.warn("failed to notify callback"; ex); } } } /**
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