Name
Abstract | ||
|---|---|---|
We consider a scenario where we want to query a large dataset that is stored in external memory and does not fit into main memory. The most constrained resources in such a situation are the size of the main memory and the number of random accesses to external memory. We note that sequentially streaming data from external memory through main memory is much less prohibitive. We propose an abstract model of this scenario in which we restrict the size of the main memory and the number of random accesses to external memory, but admit arbitrary sequential access. A distinguishing feature of our model is that it allows the usage of unlimited external memory for storing intermediate results, such as several hard disks that can be accessed in parallel. In this model, we prove lower bounds for the problem of sorting a sequence of strings (or numbers), the problem of deciding whether two given sets of strings are equal, and two closely related decision problems. Intuitively, our results say that there is no algorithm for the problems that uses internal memory space bounded by N1−ϵ and at most o(log N) random accesses to external memory, but unlimited “streaming access”, both for writing to and reading from external memory. (Here, N denotes the size of the input and ϵ is an arbitrary constant greater than 0.) We even permit randomized algorithms with one-sided bounded error. We also consider the problem of evaluating database queries and prove similar lower bounds for evaluating relational algebra queries against relational databases and XQuery and XPath queries against XML-databases. |
Year | DOI | Venue |
|---|---|---|
2009 | 10.1145/1516512.1516514 | J. ACM |
Keywords | Field | DocType |
data streams,query optimization,abstract model,semi-structured data,internal memory space,xml,lower bound,related decision problem,one-sided bounded error,random access,unlimited external memory,external memory,real-time data,arbitrary sequential access,query processing,main memory,additional key words and phrases: complexity | Query optimization,Semi-structured data,Discrete mathematics,Data stream mining,XML,Real-time data,Computer science,Theoretical computer science,Auxiliary memory | Journal |
Volume | Issue | ISSN |
56 | 3 | 0004-5411 |
Citations | PageRank | References |
9 | 0.53 | 20 |
Authors | ||
3 | ||
Name | Order | Citations | PageRank |
|---|---|---|---|
| Martin Grohe | 1 | 2280 | 127.40 |
| André Hernich | 2 | 87 | 8.30 |
| Nicole Schweikardt | 3 | 526 | 37.82 |