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Showing entries 1 to 10 of 48 10 Older Entries

Displaying posts with tag: Waffle Grid (reset)

Filtering by table is now possible with WaffleGrid
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Since I have been a home recently, I put some time correcting bugs in WaffleGrid and adding new features. Thanks to gdb, I have been able to understand a silly bug that was affecting WaffleGrid with sysbench but, weird enough, not with dbt2. Everything is in the way connections are established. I will blog more about that soon.

Regarding the new features, it is now possible to choose which tables you want to push to memcached. For that purpose, two new parameters have been introduce:

innodb_memcached_table_filter_enable = 0 | 1   (default to 0)

to enable the filtering and

innodb_memcached_table_list = db1/table1,db2/table2   

to list the tables. …

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You know you have really screwed up when …
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You crash MySQL/Innodb and you trace the error to a function that says:

“This function checks the consistency of an index page when we do not
know the index. This is also resilient so that this should never crash
even if the page is total garbage. ”

Oops… I guess its not that resilient after all:)

Waffle Grid Like Features in EnterpriseDB
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Yves pointed this out to me:

“Moving beyond just providing Oracle compatibility, EnterpriseDB is adding new scalability features to their database. One of them is a feature called ‘”Infinite Cache,” which is based on the open source memcached application.

Mlodgenski commented that distributed memory caches are common, though management from a system management and a database perspective is often difficult.

“What we did is we took the distributed memory cache that was sitting in front of the database and put it behind the database,” Mlodgenski said. “This allows a simple SQL (define) …

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Testing Waffle
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So Ronald Bradford has been getting some EC2 AMI’s setup for Waffle the last couple of days. Really he is the first person to work with us on testing out the 0.5 cream release. It’s funny but when you are heads down in the code you tend to overlook some of the easy and obvious bugs. Just by having him walk through the install we have opened up several new bugs and come up with some new Idea’s on how to make things easier in the future. I hope by early next week we can have some of annoying bugs fixed and code pushed to launchpad. When that happens I would encourage others to give it a whirl and help us make Waffle Grid better …

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WaffleGrid: Cream Benchmarks, stable and delivering a 3x boost
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Lets get down to how the latest version of Waffle Grid performs.

Starting off simple lets look at the difference between the wafflegrid modes. As mentioned before the LRU mode is the “classic” Waffle Grid setup. A page is put into memcached when the page is removed from the buffer pool via the LRU process. When a page is retrieved from memcached it is expired so its no longer valid. In the New “Non-LRU” mode when a page is read from disk, the page is placed in memcached. When a dirty page is flushed to disk, this page is overwritten in memcached. So how do the different modes perform?

4GB Memcached, Read Ahead Enabled TPM …
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WaffleGrid: 0.5 Cream Release
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I wanted to let everyone know that we are releasing Waffle Grid 0.5 code named Cream. This release fixes the nasty secondary index bug that plagued the butter release. I have been running tests on this code base for about a week straight with no errors. While I think this release is much more stable I would remind everyone this is still not a fully GA release. This release includes the ability to choose the mode of Waffle grid. By setting innodb_memcached_enable to 1, we will push pages to memcached when a disk read is done or when a page write is done, setting this to 2 will enable the classic LRU mode. If you decide to set this to 1 ( non-lru) I would recommend using the standard memcached, as …

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Waffle: Progress and a Rearchtecture?
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So I spent several hours over the last few days on the Secondary index bug. Out of frustration I decided to try and bypass the LRU concept all together and try going to a true secondary page cache. In standard Waffle a page is written to memcached only when it is expunged ( or LRU’d ) from the main buffer pool. This means anything in the BP should not be in memcached. Obviously with this approach we missed something, as Heikii pointed out in a comment to a previous post, it seems likely we are getting an old version of a page. Logically this could happen if we do not correctly expire a page on get or we bypass a push/lru leaving an old page in memcached to be retrieved later on.

So I …

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Waffle: The Mystery Continues
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So I spent the weekend looking at places where we may have missed something in the code for waffle. You can actually see some of the stuff I tried in the bug on launchpad about this, but the weird thing is the very last thing I tried. As I took a step back and looked at the problem ( secondary index corruption ) and our assumption that we “missed” something, I decided to find the place where pages are written to disk and to push to memcached from here as well as from the LRU. With the double write buffer enabled that place should be buf_flush_buffered_writes. By pushing to memcached here we should eliminate the …

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Waffle: limiting the space ids being pushed to memcached
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If you read Yves blog post about waffle yesterday we are seeing some weird gremlins in the system and could use some scoobey doo detective work if you have some ideas. The strange thing is it only exhibits under high load. So it really seems like we may have missed some background cleanup process that accesses or removes pages from disk or the buffer pool without going through the functions we call waffle in (buf_LRU_search_and_free_block & buf_read_page_low ).

One of the idea’s I had was trying to narrow the scope of what’s being pushed and read form Memcached. Even though I am using file per table, system …

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What’s up with WaffleGrid?
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You probably haven’t noticed but I have not blogged since the UC. It is not because I am upset by the perspective of working for Oracle, I have simply been busy tracking down an issue we have with WaffleGrid. We discovered that under high load, with DBT2 on a tmpfs, we end up with error in a secondary index. In the error of MySQL, we have entries like this one:

InnoDB: error in sec index entry update in
InnoDB: index `myidx1` of table `dbt2`.`new_order`
InnoDB: tuple DATA TUPLE: 3 fields;
 0: len 4; hex 80000001; asc     ;;
 1: len 4; hex 80000bea; asc     ;;
 2: len 4; hex 80000005; asc     ;;

InnoDB: record PHYSICAL RECORD: n_fields 3; compact format; info bits 32
 0: len 4; hex 80000001; …
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Showing entries 1 to 10 of 48 10 Older Entries

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