optimizer-hints | 易学教程

Does GCC inline C++ functions without the 'inline' keyword?

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问题 Does GCC, when compiling C++ code, ever try to optimize for speed by choosing to inline functions that are not marked with the inline keyword? 回答1: Yes. Any compiler is free to inline any function whenever it thinks it is a good idea. GCC does that as well. At -O2 optimization level the inlining is done when the compiler thinks it is worth doing (a heuristic is used) and if it will not increase the size of the code. At -O3 it is done whenever the compiler thinks it is worth doing, regardless

When to use hints in oracle query [duplicate]

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问题 This question already has an answer here : When to use Oracle hints? (1 answer) Closed 2 years ago . I have gone through some documentation on the net and using hints is mostly discouraged. I still have doubts about this. Can hints be really useful in production specially when same query is used by hundreds of different customer. Is hint only useful when we know the number of records that are present in the tables? I am using leading in my query and it gives faster results when the data is

make the optimizer use all columns of an index

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问题 we have a few tables storing temporal data that have natural a primary key consisting of 3 columns. Example: maximum temperature for this day. This is the Composite Primary key index (in this order): id number(10): the id of the timeserie. day date: the day for which this data was reported kill_at timestamp: the last timestamp before this data was deleted or updated. Simplified logic: When we make a forecast at 10:00am, then the last entry found for this id/day combination has his create_at

make the optimizer use all columns of an index

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we have a few tables storing temporal data that have natural a primary key consisting of 3 columns. Example: maximum temperature for this day. This is the Composite Primary key index (in this order): id number(10): the id of the timeserie. day date: the day for which this data was reported kill_at timestamp: the last timestamp before this data was deleted or updated. Simplified logic: When we make a forecast at 10:00am, then the last entry found for this id/day combination has his create_at changed to 9:59am and the newly calculated value is stored with a kill_at timestamp of '31.12.2999'.

Stored procedures and OPTIMIZE FOR UNKNOWN

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I've read up on the SQL Server 2008 OPTIMIZE FOR UNKNOWN query hint. I understand how it works. However, I have a question on where and when to use it. It cannot be specified inside a UDF. It can be specified inside a stored proc. However, this MSDN blog post states the following: 4.Moving a query into a stored procedure can put it into a separate procedural context and can be a good way to get that value visible to the optimizer (Note: this works in SQL 2000 as well) That seems to me to be saying that any parameter passed to a stored proc will be "sniffed", thereby helping SQL Server to

What can happen as a result of using (nolock) on every SELECT in SQL Server?

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I get that the (nolock) optimizer hint allows for "dirty reads", but under what very specific scenarios is this a bad idea? I've never seen such widespread use of (nolock) in an organization, and it makes me nervous. I'd like an explanation in terms of user stories. "Paul does A, Peter does B, X happens instead of Y". Quassnoi Reposting this answer: NOLOCK means placing no locks at all. Your query may returns portions of data as of before UPDATE and portions as of after UPDATE in a single query . Like, a debit without a credit and these kinds of stuff. For instance, I just ran this query on a

Stored procedures and OPTIMIZE FOR UNKNOWN

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问题 I've read up on the SQL Server 2008 OPTIMIZE FOR UNKNOWN query hint. I understand how it works. However, I have a question on where and when to use it. It cannot be specified inside a UDF. It can be specified inside a stored proc. However, this MSDN blog post states the following: 4.Moving a query into a stored procedure can put it into a separate procedural context and can be a good way to get that value visible to the optimizer (Note: this works in SQL 2000 as well) That seems to me to be

What can happen as a result of using (nolock) on every SELECT in SQL Server?

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问题 I get that the (nolock) optimizer hint allows for "dirty reads", but under what very specific scenarios is this a bad idea? I've never seen such widespread use of (nolock) in an organization, and it makes me nervous. I'd like an explanation in terms of user stories. "Paul does A, Peter does B, X happens instead of Y". 回答1: Reposting this answer: NOLOCK means placing no locks at all. Your query may returns portions of data as of before UPDATE and portions as of after UPDATE in a single query .

Does GCC inline C++ functions without the 'inline' keyword?

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Does GCC, when compiling C++ code, ever try to optimize for speed by choosing to inline functions that are not marked with the inline keyword? Yes. Any compiler is free to inline any function whenever it thinks it is a good idea. GCC does that as well. At -O2 optimization level the inlining is done when the compiler thinks it is worth doing (a heuristic is used) and if it will not increase the size of the code. At -O3 it is done whenever the compiler thinks it is worth doing, regardless of whether it will increase the size of the code. Additionally, at all levels of optimization (enabled