robertzk / RPostgres

A DBI-compliant interface to PostgreSQL

RPostgres

RPostgres is an DBI-compliant interface to the postgres database. It's a ground-up rewrite using C++ and Rcpp. Compared to PostgresSQL, it:

• Has full support for parameterised queries via dbSendQuery(), and dbBind().

• Automatically cleans up open connections and result sets, ensuring that you don't need to worry about leaking connections or memory.

• Is a little faster, saving ~5 ms per query. (For refernce, it takes around 5ms to retrive a 1000 x 25 result set from a local database, so this is decent speed up for smaller queries.)

• A simplified build process that relies on system libpq.

Installation

RPostgres isn't available from CRAN yet, but you can get it from github with:

# install.packages("devtools")
devtools::install_github("RcppCore/Rcpp")
devtools::install_github("rstats-db/DBI")
devtools::install_github("rstats-db/RPostgres")

Basic usage

library(DBI)
# Connect to the default postgres database
con <- dbConnect(RPostgres::Postgres())

dbListTables(con)
dbWriteTable(con, "mtcars", mtcars)
dbListTables(con)

dbListFields(con, "mtcars")
dbReadTable(con, "mtcars")

# You can fetch all results:
res <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
dbFetch(res)
dbClearResult(res)

# Or a chunk at a time
res <- dbSendQuery(con, "SELECT * FROM mtcars WHERE cyl = 4")
while(!dbHasCompleted(res)){
  chunk <- dbFetch(res, n = 5)
  print(nrow(chunk))
}
# Clear the result
dbClearResult(res)

# Disconnect from the database
dbDisconnect(con)

Connecting to a specific Postgres instance

library(DBI)
# Connect to a specific postgres database i.e. Heroku
con <- dbConnect(RPostgres::Postgres(),dbname = 'DATABASE_NAME', 
                 host = 'HOST', # i.e. 'ec2-54-83-201-96.compute-1.amazonaws.com'
                 port = 5432, # or any other port specified by your DBA
                 user = 'USERNAME',
                 password = 'PASSWORD')

Design notes

The original DBI design imagined that each package could instantiate X drivers, with each driver having Y connections and each connection having Z results. This turns out to be too general: a driver has no real state, for PostgreSQL each connection can only have one result set. In the RPostgres package there's only one class on the C side: a connection, which optionally contains a result set. On the R side, the driver class is just a dummy class with no contents (used only for dispatch), and both the connection and result objects point to the same external pointer.