What is special about internal design of LMDB? -


what performance difference (reads/writes) between c++ implementation of in-memory b-tree (for example google btree) , lmdb (without taking consideration feacures of lmdb such transactions, isolation, shared access etc.)?

this 2014 lmdb design presentation architect howard chu covers design , tradeoffs of lmdb.

to summarize: lmdb copy-on-write, bottom-up updated, double-buffered, b-tree implementation favors simplicity whenever clashes other considerations.

the smart design choices make 1 of highest performance , corruption-resistant b-tree implementations out there.

  • copy-on-write means data never overwritten avoiding many possible corruption scenarios
  • bottom-up updates leaf root make root update equivalent commit
  • double buffering of past versions keeps last-two roots in db file
  • complex multi-level caching schemes avoided - lmdb relies on underlying os caching
  • the whole code base small compared other dbs avoiding cpu cache misses

obviously, these choices mean lmdb not friendly complex scenarios such as:

  • multi-version db rollbacks (only last 2 available)
  • long-lived transactions , delayed commits: these lead append-only behavior , potentially unlimited growth of db file
  • multiple concurrent writers: lmdb favors simpler multiple readers , single writer schemes

there's more in full (over 100 pages) presentation. above summary of spirit of lmdb.

lmdb used core storage engine in prominent open source projects such open ldap , memcached , in both cases speed-ups of orders of magnitude have been observed compared alternatives can seen in micro-benchmark results.


Comments

Post a Comment

Popular posts from this blog

java - pagination of xlsx file to XSSFworkbook using apache POI -

right in code, reading xlsx file, xssfworkbook, , writing database. but, when size of xlsx file increases, causes outofmemory error. can not increase server size, or divide xlsx file pieces. tried loading workbook using file (instead of inputstream), didn't either. i looking way read 10k rows @ time (instead of entire file @ once) , iteratively write workbook , database. is there way apache poi? poi contains called "eventmodel" designed purpose. it's mentioned in faq : the ss eventmodel package api reading excel files without loading whole spreadsheet memory. require more knowledge on part of user, reduces memory consumption more tenfold. based on awt event model in combination sax. if need read-only access, best way it. however, may want double check first if issue somewhere else. check out this item : i think poi using memory! can do? 1 comes quite lot, reason isn't might think. so, first thing check - what's source of prob...
Read more

Unlimited choices in BASH case statement -

consider simple bash snippet: case $option in 1) image=${options[0]%.tar} ;; 2) image=${options[1]%.tar} ;; 3) image=${options[2]%.tar} ;; 4) image=${options[3]%.tar} ;; *) echo "invalid option" exit 1 esac in real script numbers goes 30. makes pretty long. can somehow specify cases variable? something this: case $option in $i) image=${options[$(($i-1))]%.tar} any pointer appreciated. you can match against multiple patterns in single clause: case $option in 1|2|3: echo "$option one, 2 or three" ;; esac if still typing you, can use simple pattern matching: case $option in # following matches # - single-digit numbers 0-9 # - two-digit numbers starting either 1 or 2 # - number 30 [0-9]|[12][0-9]|30) image=${options[$(($option-1))]%.tar} ;; *) echo "invalid option" 1>&2 exit 1 esac
Read more

apache - How do I stop my index.php being run twice for every user -

we've got webapp initial html served using apache , php. i noticed index.php being run twice every request. seems caused / effected rewrite rules in our .htaccess - rewritecond %{http_host} ^(www\.|hotels\.)ourdomain\.com$ [nc,or] rewritecond %{server_name} ^(www\.|hotels\.)ourdomain\.com$ [nc] rewriterule (.*) http://ourdomain.com/$1 [r=301] rewriterule ^hotels/([^/]+)/?\??(.*)$ ?d=$1&$2 [qsa] the final rule moving parameter url path query string. i.e. http://ourdomain.com/hotels/vegas?someparam=1 becomes http://ourdomain.com?d=vegas&someparam=1 if go directly query string version index.php run once. if use url redirected, index.php run twice (i'm checking adding error_log('end of index.php') file). so example going http://ourdomain.com/hotels/paris hits file twice http://ourdomain.com?d=paris hits once. i've seen this question , had @ blog mentioned , , can't find empty string url's (i've tried using yslow process). ...
Read more