Using web BLAST, you may be searching against a large database. For efficient processing, BLAST internally breaks up a large database into smaller and more manageable parts (volumes). BLAST generates the final sequence alignments from matches in all volumes.
Large queries and/or excessive matches to sequences in the database may cause numerous opened volumes at the same time. That can result in exceeding the capacity of the system. On your end, you will experience the “Process size limit exceeded” error.

How can you avoid this problem?

To avoid this error (and those related to CPU time out), you can reduce computational load of your search in several ways:  

• Use a smaller query or specify a query subrange.
• Target a smaller BLAST database.
• Use organism limit to target a smaller subset in the database.
• Select a larger word size.
• Lower the expect value.
• Decrease Max target sequences.

• BLAST locally by downloading BLAST databases from NCBI and using BLAST+ executables.
• ElasticBLAST on the cloud.

Where can you learn more?

Related knowledge articles on web BLAST limitations, errors, and preventive measures:

• Why does my BLAST search get a “CPU usage limit was exceeded” error?
• How many sequences can I enter in a single BLAST search?
• How does BLAST penalize heavy usage from an IP address?
• How do I reduce search load to avoid being penalized for heavy usage when teaching BLAST in a classroom?

• Web BLAST Quick Start Guide