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30
votes
3answers
11k views

Parameter Sniffing vs VARIABLES vs Recompile vs OPTIMIZE FOR UNKNOWN

So we had a long running proc causing problems this morning (30 sec + run time). We decided to check to see if parameter sniffing was to blame. So, we rewrote the proc and set the incoming ...
27
votes
5answers
15k views

Why would I NOT use the SQL Server option “optimize for ad hoc workloads”?

I've been reading some great articles regarding SQL Server plan caching by Kimberly Tripp such as this one: http://www.sqlskills.com/blogs/kimberly/plan-cache-and-optimizing-for-adhoc-workloads/ Why ...
15
votes
6answers
12k views

PostgreSQL: Force data into memory

Is there a systematic way to force PostgreSQL to load a specific table into memory, or at least read it from disk so that it will be cached by the system?
13
votes
2answers
5k views

Is the overhead of frequent query cache invalidation ever worth it?

I'm currently working on a MySQL database where we are seeing a large number of invalidations from the query cache, primarily because of the high number of INSERT, DELETE and UPDATE statements that ...
10
votes
2answers
3k views

PostgreSQL Index Caching

I'm having difficulty finding 'lay' explanations of how indexes are cached in PostgreSQL, so I'd like a reality check on any or all of these assumptions: PostgreSQL indexes, like rows, live on disk ...
10
votes
1answer
773 views

Definitive list of steps for SQL Server baseline testing?

Before running a performance test / baseline for an app that uses SQL Server, I want to be able to set the instance to a "clean" state, without restarting the instance. There are steps I tend to ...
9
votes
1answer
425 views

Where does an execution plan come from?

Is there a way I can determine if a plan was just generated for a particular query, or was found in the plan cache?
8
votes
1answer
5k views

Qcache_free_memory not full yet I get alot of Qcache_lowmem_prunes

I just started dabbling with the query cache for our CMS. Can anyone tell me (or at least give a good guess) why I get a lot of Qcache_lowmem_prunes when more than half of Qcache_free_memory is free? ...
8
votes
3answers
5k views

How to boost performance of virgin queries in MS SQL Server?

I have ASP.NET web site that does it's own independent caching of data and data does not change for long periods of time, so it does not need to query SQL Server second time with same query. I need to ...
7
votes
1answer
738 views

How much memory is a table taking up?

Is there a way to find out how much memory a table is taking up in SQL Server (2005 and greater)? For example, suppose I have a table with 30 million records. I'd like to know how many pages ...
7
votes
2answers
1k views

How to calculate cache misses for PostgreSQL

I'm administering a server where a tool using a PostgreSQL runs. The tool takes care of most PostgreSQL configurations by itself, but I'm observing some performance problems. I could confirm at OS ...
6
votes
1answer
129 views

Procedure Cache Dropping

We've experienced an issue with SQL Server dropping proc cache out of the blue. I'm talking 4GB down to 0 in 2 minutes. This has occurred approx once per day in the last two weeks. It does happens ...
6
votes
2answers
360 views

mysql performance / cache configuration enigma [closed]

I have two mysql 5.1 instances (say A, B) hosting the same database schema. If I run (with mysql workbench) the same query on both instances I don't understand why I get very different response times ...
5
votes
1answer
294 views

Why does a SELECT statement dirty cache buffers in Postgres?

I am running EXPLAIN (ANALYZE, BUFFERS) SELECT ... in my Postgres 9.3 server. I end up seeing something like Buffers: shared hit=166416 dirtied=2 in the output. From the documentation, "dirtied" ...
5
votes
2answers
1k views

Sudden performance decrease in SQL Server

I've got a problem with a SQL Server 2008 R2 instance. Last week the performance suddenly broke down. All inserts are very very slow. It takes 4-5 times longer than before. On the hardware we found no ...
5
votes
1answer
60 views

To minimize Cache misses in PostgreSQL?

You can calculate cache misses as described here. However, I am interested in how to minimize the phenomenon in PostgreSQL 9.4.3 on x86_64-unknown-linux-gnu, compiled by gcc (Debian 4.9.2-10) 4.9.2, ...
4
votes
1answer
12k views

Difference between FreeProcCache and FreeSystemCache

Currently I run DBCC FREEPROCCACHE when I want to wipe information out of the buffer pool between running SQL queries. However, I was reviewing this Technet article referencing DBCC FREESYSTEMCACHE. ...
4
votes
1answer
597 views

Reindexing and its effects on SQL cache

Currently looking into reindexing our sql database, and cannot find any information on whether or not the procedure cache would be effected. Any help or information would be great. We are using SQL ...
4
votes
1answer
349 views

Buffer usage for index with no reads

Using SQL Server 2008 R2, the main transactional table in a vendor database is massive compared to all others and has about 14 indexes. Some of these indexes don't get used in our environment, but we ...
4
votes
2answers
207 views

MySQL: Is it safe to have a table with multiple millions of rows?

I have a very complex search query to write that will touch many tables, have conditions and joins. For efficiency reasons, I am strongly considering creating a "cache table" where I would maybe once ...
4
votes
2answers
8k views

query_cache_type = 0 vs query_cache_type = 1

Recently, I moved from standard MySQL to Percona, and used the Percona Wizard to generate my.cnf. However, I can see that, by default, the generated settings for my.cnf use query_cache_type = 0. ...
4
votes
1answer
224 views

Can I partially invalidate the MySQL table cache?

I want to set a fairly large table to MyISAM mode to keep it cached proactively. The table file is approximately 3GB. After several hours, MySQL invalidates the entire table from cache, while < ...
4
votes
1answer
44 views

Does MySQL/InnoDB use table caches when dealing with foreign tables?

TL;DR: Does a table referred to via schema.table get held in table cache? I have a large number of client databases that our application connects to based on an http request. These are used for every ...
3
votes
5answers
5k views

Why is MySQL caching data on our dynamic PHP site?

We are having an annoyance with our PHP/MySQL site in that it seems to cache data from the database and our PHP pages are showing out of date records. In fact, there are pages that link to URLs that ...
3
votes
2answers
777 views

MySQL cache is not getting hit by subqueries

I noticed something weird on MySQL query_cache behavior and I would like to know if this is a normal behavior. Let's say I have an item table ID | Item ----------- 1 | Item_1 2 | Item_2 3 | ...
3
votes
2answers
3k views

Does Oracle cache queries when using a database link

Some vendor told us that we should not use database link between our database and theirs as the queries executed over a database link would not be cached, nor optimized. I can't find any information ...
3
votes
1answer
319 views

How can I identify queries that are producing cache misses in Postgres?

I have a Postgres database with a total data size of 115GB. The server has ~60GB of memory. The index cache hit rate is holding at 99%+ but the table cache hit rate has fallen to ~97%. I am trying ...
3
votes
1answer
145 views

Postgres caching and bytea

I have a DB which, among other things, stores images (as bytea, if that's interesting). It also stores users' metadata, activity logs, etc., but images currently take 500MB out of the total 600MB ...
3
votes
2answers
126 views

Stored Procedure slow after weekend

When I come to work on monday some stored procedures take several minutes to execute and STATISTICS IO shows a lot of PHYSICAL READS and READ AHEADS going on. However, after running the procedures ...
2
votes
2answers
248 views

Can I tell MySQL what to cache?

Pretty straightforward question: Let's say I have a specific query that I know is regularly used, can I tell MySQL to always cache it "automatically" ... i.e. once the cached query results are ...
2
votes
1answer
2k views

How bad is query plan pollution (too many equivalent plans in cache)?

Question currently affects C#/.NET, DB access based on ADO.NET and SQL Server 2008 R2, but I think it applies to other databases as well. I noticed some old modules of a system have non-optimal SQL ...
2
votes
1answer
483 views

user permission cache in session or check from database?

On each page of my websites 2 or 3 permissions have to be checked and I use role-permission model. Which one is better? to check permissions of each user always through database directly or once ...
2
votes
1answer
1k views

Mysql: Tell InnoDB to keep a specific table or database out of pool/cache?

I have some tables that are used primarily to keep historical data, or that are only used once a day. I do not want any operations on these tables to disrupt the more important tables present in ...
2
votes
1answer
74 views

SQL Server Cache population on server / service startup

We have upgraded our SQL Server instance with buckets of RAM, so it can now much more effectively cache . The issue is that it takes time (days) to populate the cache. As far as I understand this is ...
2
votes
0answers
89 views

Denormalization vs Cached Data [closed]

I'm in a dilemma about denormalization of the database vs. caching the joint query results of the database. We have 2 tables. Let's say A and B. A may have many of Bs but B can be belong to only one ...
2
votes
0answers
147 views

SELECT stuck giving results from the query result cache, though table has changed

A process that runs every two minutes or so started to misbehave. We noticed it was because the cursor fetched repeatedly 0 rows, even if indeed there were new rows satisfying the conditions in the ...
1
vote
1answer
7k views

What is wrong with table_cache hit rate?

In my.cnf I have: table_cache = 524288 open_files_limit = 65535 Both are at max allowed value for mysql config. Both are less than max open file limit: # cat ...
1
vote
2answers
176 views

Functioning of Oracle's Server result Cache

I am reading the Oracle concepts doc and have a doubt [about general cache mechanism ] : PL/SQL function code can include a request to cache its results. Upon invocation of this function, the ...
1
vote
1answer
29 views

What will happen with cached index or table when it is modified, will it stay in cache?

if PostgreSQL loads something (for example an index) into cache, what happens if it (cached index) gets modified? Is it going to be removed from cache or not?
1
vote
1answer
287 views

Would daily/weekly db memory cache clearing be of use?

So memory use is hitting limits. Would clearing the database memory cache on a daily/weekly schedule be of use? (Ignoring the fact I probably should be looking at reducing size of database/indexes) ...
1
vote
1answer
103 views

PostgreSQL: cache, disk, replication. What order?

I am thinking of using two servers in Master/Slave replication I want to add following condition: RAM size = dataset size * x, where x > 2. After that, I plan to force PGSQL to keep all data in RAM ...
1
vote
1answer
128 views

Where do caching servers conceptually fit in my architecture?

Given the simple well-known architecture below: Where (conceptually) does the caching server(s) sit?
1
vote
3answers
262 views

getting error while starting memecached service with ndb engine

i am installed memcached library by following the steps in the internet. now there is a binary file created in bin folder of mysql now i exicuting the command memcached i am getting error like this ...
1
vote
1answer
128 views

Battery backed write cache and Postgres

I will be getting a SAN with a battery backed write cache for a new Postgres data warehouse and am not sure what settings to apply to make proper use of it. If the cache is enabled in the SAN is that ...
1
vote
1answer
488 views

Does MySQL's MyISAM use cache before insert?

I want to test two different Disks, one of them is HDD and another is SSD I use exactly same information and app for both servers. They are exactly same, just one of them is SSD and another is HARD. ...
1
vote
1answer
92 views

how to use mysql temporal cache tables

I took this example from a book where visitors_today is the cache table from visitor_stored. The idea is to store all the visitors per day (visitors_stored) using a cache table. Create table ...
1
vote
1answer
70 views

Different plans or buffers for different connections?

We had an issue in our dev environment where a procedure call timed out from the web server after 30 seconds. I traced the query and ran it manually (same params and all) from SSMS and it executed in ...
1
vote
1answer
25 views

What are the consequences of enabling slow_query_log and flushing the cache on mysql?

I have a large database that is performing poorly recently. I want to enable the slow_query_log to investigate the queries and flushing the cache but I need to know what are the consequences of doing ...
1
vote
1answer
253 views

MySQL: can a table get stuck in the table cache?

I've asked this question on the ServerFault stackexchange, someone directed me here. I'm a PHP developer and am responsible for a set of PHP scripts that run on a shared host running FreeBSD, that ...
1
vote
1answer
269 views

Query_cache doesn't work with join

I have a simple join query, but for some reason query_cache won't cache it! SELECT id, news, approve, FIXED, DATE, allow_main FROM post LEFT JOIN post_plus ON post.id = post_plus.news_id WHERE ...