Sloan Digital Sky Survey
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Query Timeouts and Row Limits

Due to the sheer size of the SDSS database, queries that search the entire multi-TB database, or queries that are not formulated in the most efficient way, can take a very long time to execute (hours). To be fair to other users and prevent the CAS from bogging down, the SkyServer search tools have built-in timeouts and row limits (max. number of rows in query results). These are listed below for each query tool.

There is also a limit on how many queries you can submit per minute from a given client. This is to prevent crawlers from hogging the system by submitting several queries per second and making the server unusably slow for other users. Currently, you are allowed to submit 60 queries per minute, i.e., if you submit one query, you must wait at least 1 seconds before you submit the next one.

If your query is timing out, please see the Optimizing Queries section of the SQL Intro Page.

If you absolutely need to run a query that does not fit within these limits, you can use the Batch Query system (CasJobs), which lets you run longer queries in separate queues and lets you maintain your own storage space on the DB server (MyDB).

If none of these options work, we may be able to make special arrangements for you to obtain the data that you need. Please contact the helpdesk in that case.

Query Tool Timeouts and Row Limits

Tool/Page Timeout (sec) Row Limit Remarks
SQL Search 600 500000 Browsers cannot render large outputs
Object Crossid 1800 500000 Applies to both Upload and Speclist
Form Query 600 500000 Imaging (IQS) and Spectro (SQS)
Visual Tools 600 NA Finding, Navigate, Image Lists
sdssQA 3600 No limit Downloadable Java client
CasJobs No limit No limit Batch Query Service
Default 600 500000 Defaults when none of the above limits apply