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Select count(*) from `pg_table_def` takes minutes on Amazon Redshift

concurrent query performance in amazon redshiftAmazon Redshift for SaaS applicationEfficient GROUP BY a CASE expression in Amazon Redshift/PostgreSQLRedshift SELECT * performance versus COUNT(*) for non existent rowAmazon redshift: bulk insert vs COPYing from s3Amazon Redshift doing Hash Join even when joined on column that is both Dist Key and Sort KeyRedshift select * vs select single columnis “INSERT INTO SELECT” free from race conditions in redshiftRedshift DELETE using slow Hash Join while equivalent SELECT uses Merge JoinSelect from a wide table in redshift with where clause on any column

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Why might a count from pg_table_def in Redshift take more than 2 minutes?

I'm debugging a consistently slow query (exceeds a 4 minute timeout) that lists all tables and columns in a certain schema. However, the slowness is reproducible with the simpler query below:

redshift-psql=> SELECT COUNT(*) from pg_table_def;
 count
-------
 5067
(1 row)

Time: 144956.109 ms

amazon-web-services amazon-redshift

share|improve this question

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I am guessing network plays a role in your case. You need to take a look it from that aspect, I have ran the same query on my Redshift cluster and it took 0.18 seconds
  
  – mdem7
  Mar 26 at 22:24
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Also the workload at the same time you are running this query on the cluster might play a role
  
  – mdem7
  Mar 26 at 23:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You need to understand how WLM works on Redshift - that query time also includes time the query is potentially queued waiting for a query slot. As per above comment, if you have a lot of concurrent queries (or very few WLM slots) then the query could be queued waiting for other queries to complete. Does your cluster have SQA (short query acceleration) enabled?
  
  – Nathan Griffiths
  Mar 29 at 0:44
  

  
  
  
  

add a comment | 

1

1

Why might a count from pg_table_def in Redshift take more than 2 minutes?

I'm debugging a consistently slow query (exceeds a 4 minute timeout) that lists all tables and columns in a certain schema. However, the slowness is reproducible with the simpler query below:

redshift-psql=> SELECT COUNT(*) from pg_table_def;
 count
-------
 5067
(1 row)

Time: 144956.109 ms

amazon-web-services amazon-redshift

share|improve this question

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I am guessing network plays a role in your case. You need to take a look it from that aspect, I have ran the same query on my Redshift cluster and it took 0.18 seconds
  
  – mdem7
  Mar 26 at 22:24
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Also the workload at the same time you are running this query on the cluster might play a role
  
  – mdem7
  Mar 26 at 23:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You need to understand how WLM works on Redshift - that query time also includes time the query is potentially queued waiting for a query slot. As per above comment, if you have a lot of concurrent queries (or very few WLM slots) then the query could be queued waiting for other queries to complete. Does your cluster have SQA (short query acceleration) enabled?
  
  – Nathan Griffiths
  Mar 29 at 0:44
  

  
  
  
  

add a comment | 

Why might a count from pg_table_def in Redshift take more than 2 minutes?

I'm debugging a consistently slow query (exceeds a 4 minute timeout) that lists all tables and columns in a certain schema. However, the slowness is reproducible with the simpler query below:

redshift-psql=> SELECT COUNT(*) from pg_table_def;
 count
-------
 5067
(1 row)

Time: 144956.109 ms

amazon-web-services amazon-redshift

share|improve this question

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

redshift-psql=> SELECT COUNT(*) from pg_table_def;
 count
-------
 5067
(1 row)

Time: 144956.109 ms

share|improve this question

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

share|improve this question

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges

asked Mar 26 at 20:33

JoeJoe

1,06111 gold badge1414 silver badges3434 bronze badges