Synonyms in SQL Server are designed to simplify object references, acting as aliases for database objects like tables or views. They can streamline your SQL code and enhance readability, especially when dealing with complex database structures or cross-database queries. However, like any database feature, understanding their potential impact on performance is crucial. One user encountered a perplexing situation where a stored procedure utilizing a synonym unexpectedly suffered from slow execution times, highlighting a potential, albeit unclear, link between Synonym Servers and query performance.
The Case of the Sluggish Synonym
The issue arose with two stored procedures that were virtually identical. The key difference lay in how they referenced the target table. One procedure, designed for local database access, directly referenced the table. The other, intended for what might be termed a “synonym server” scenario, accessed the same table via a synonym. This synonym was fully qualified, including the server name, database, schema, and table name, even though both databases resided on the same server. Interestingly, initially, a newly created “local” procedure performed as expected, quickly retrieving data. However, the procedure using the synonym, pointing to what we can consider the “synonym server” table, exhibited significant slowness.
The Unexpected Fix: Statistics Update
Troubleshooting the slow synonym procedure proved challenging, especially since obtaining an execution plan for the stalled query was impossible. However, in a surprising turn of events, updating the statistics on the underlying table seemed to resolve the performance bottleneck. After updating statistics and recompiling the synonym-utilizing procedure, performance returned to normal. The perplexing part remains: why did updating statistics have such a pronounced effect in this scenario? The “local” procedure, created around the same time, worked efficiently even before the statistics update. This suggests the synonym, or perhaps the way SQL Server handles statistics in conjunction with synonyms, might play an unexpected role in query performance.
Synonyms and SQL Server Performance – Key Takeaways
While the exact cause remains somewhat elusive – whether it’s directly related to the synonym itself or a confluence of factors – this experience offers a valuable lesson. If you encounter slow query performance involving synonyms, especially in scenarios that might resemble a “synonym server” setup, consider updating statistics on the base tables as a potential quick resolution. It might be the unexpected key to unlocking performance and resolving your SQL Server performance mysteries when synonyms are in play.
