… fetched from step 1, and when the buffer is full sort them by pk_column, and do a range …mrr_rowid_refills + 1 MRR range scans had to be performed. As in the table above you can with default buffer … ~11min to under a minute. The query time is reduced further when buffer size is set large enough so …
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 139 Comments
… this table has 10000 distinct value, so range 1..100 selects about 1% of the table. The times for full table scan vs range scan by… order can be a lot of help for big scans. This will reduce the gap but I doubt it will be closed… with in temporary table etc. Prefer full table scans to index accesses – For large data sets full table scans are often faster than range scans and other types…
Post: Heikki Tuuri Innodb answers - Part I
October 26, 2007 By 17 Comments
… full table scan HT: No PZ: Another possible area of optimization. I frequently see batch jobs killing server performance overtaking buffer pool. Though full table scan… pool and which are not swappable. They also allow to reduce number of TLB cache misses. huge pages along however do…
Post: MySQL EXPLAIN limits and errors.
July 24, 2006 By 6 Comments
… applied. The other reason for difference is join_buffer which reduces number of passes MySQL had to perform and so number… or use temporary table with partial result set (partial rows) and than compose full rows by reading data from other tables. No information… rows to be scanned is shown but it does not tell much about cost of the operation – full table scan of table in memory may…
Post: MySQL Crash Recovery
July 30, 2006 By 26 Comments
…. In MySQL 4.1 sync_frm option was added which reduces this problem as time window when it can happen is…, innodb_buffer_pool, query_cache,table_cache) are cleaned, so may be OS caches. This may reduce performance dramatically. So if you… it can be done by issuing large index scan queries. Full table scan queries allow to preload table data ether in storage engine caches or…
Post: Performance impact of complex queries
January 17, 2007 By 11 Comments
… a lot of queries can get piled up because of reduced cache efficiency many queries may start waiting on disk at… before latency, meaning if you have query which is doing full table scan (sequential reads) its requests will be prioritized as they do… remember in Linux 2.4 times I could make single full table scan query to slow things that bad, so “ls” would take…
Post: Slow Query Log analyzes tools
September 6, 2006 By 83 Comments
… with fast and efficient queries, which just happen to do full table scans – for example if you would be having drop down list… would not lose this kind of info. Yes this will reduce your performance a bit and will require plenty of disk… to logging only very slow queries. Once you have created full log – parse it and check queries using EXPLAIN starting from…
Post: A rule of thumb for choosing column order in indexes
June 5, 2009 By 15 Comments
… with this query, which returns zero rows but does a full table scan. EXPLAIN says there are no possible_keys. SELECT * FROM tbl…
Post: When to use Hardware upgrade instead of Software Optimization
December 5, 2008 By 5 Comments
… should have a goal. You add the index to avoid full table scan and make given query faster. You add memory to avoid… remember as moving from 4 Core systems to 8 Core reduced performance for many MySQL systems even though hardware itself was…
Post: Give me 8 hours, and I'll help you build a better application
August 29, 2009 By 4 Comments
… do. At a more technical level, archiving reduces the size of your workload’s “working set” …insertion algorithms for cache control, so a single table scan can flush really interesting data out of … application actually uses? Is the disk getting full? 3. Capture and Store Historical Data Likewise, …
