Load takes too long

Your load operation can take too long for the following reasons. We suggest the following troubleshooting approaches.

COPY loads data from a single file

Split your load data into multiple files. When you load all the data from a single large file, Amazon Redshift is forced to perform a serialized load, which is much slower. The number of files should be a multiple of the number of slices in your cluster, and the files should be about equal size, between 1 MB and 1 GB after compression. For more information, see Amazon Redshift best practices for designing queries.

Load operation uses multiple COPY commands

If you use multiple concurrent COPY commands to load one table from multiple files, Amazon Redshift is forced to perform a serialized load, which is much slower. In this case, use a single COPY command.