I am using Tomcat 7.0.53, and I am using Tomcat JDBC connection pooling
to connect to multiple PostgreSQL (9.3) databases. My application is a
JAX-RS (Jersey) web server application that provides a set RESTful web
services (no UI). My data layer uses the Spring JdbcTemplate library.
First, let me say that I have everything working, and I am moving on to
tuning and optimization. I have read the Tomcat JDBC connection pool
docs, searched the web, asked a question on SO, and am still struggling
with a fairly basic concept or two.
My Java code looks pretty much like the "Plain Ol' Java" example from
the docs here:
http://tomcat.apache.org/tomcat-7.0-doc/jdbc-pool.html#Plain_Ol%27_Java
As I said, my questions are fairly fundamental, so let me state my
first, fairly safe, assumption to get this started. Please let me know
if this assumption holds water.
Assumption #1: If I run code like this twice,|the two resulting
connections will come from the same Tomcat connection pool, even though
I am instantiating two separate instances of |||PoolProperties|, each on
a separate thread in response to a separate JAX-RS web request.
PoolProperties poolProperties = new PoolProperties();
||||poolProperties.setDriverClassName("org.postgresql.Driver");
||||poolProperties.setUrl("jdbc:postgresql://myserver/db_a");
||||poolProperties.setMaxActive(10);
||||DataSource dataSource =
org.apache.tomcat.jdbc.pool.DataSource(poolProperties);
||||NamedParameterJdbcTemplate namedParameterJdbcTemplate = new
NamedParameterJdbcTemplate(dataSource);
To restate: I am assuming the two database connections for two separate
calls of this above code will both come from a single Tomcat JDBC
connection pool. Is this assumption correct?
[I will mention here that I have stripped out most of my code in order
to make the examples and discussion concise. I am actually setting
around 15 attributes on PoolProperties, but they don't matter for the
sake of this discussion. Also, the data access code is in a separate
class from the DataSource-creating code, but I show them together here
to keep it to the point.]
Next, I'll move on to my first question.
Question #1: Let's say I now run code just like the code above twice,
but connect to a different database each time. For example, first
"db_a", and then "db_b". Does a single connection pool hold connections
to both databases, or are two separate connection pools created, one for
db_a and one for db_b, each with a maxActive setting of 10? Here is what
the second run of the code would look like:
||
PoolProperties poolProperties = new PoolProperties();
||||poolProperties.setDriverClassName("org.postgresql.Driver");
||||poolProperties.setUrl("jdbc:postgresql://myserver/db_b");
||||poolProperties.setMaxActive(10);
||||DataSource dataSource =
org.apache.tomcat.jdbc.pool.DataSource(poolProperties);
||||NamedParameterJdbcTemplate namedParameterJdbcTemplate = new
NamedParameterJdbcTemplate(dataSource);
|The reason I ask, btw, is that I need to be able to control the total
number of database connections my application opens to Postgres. If
separate database pools are opened for each database URL (i.e., each
database), then the math for how to set maxActive will be quite
different than the math I would use if a single connection pool contains
all connections to all databases.
Thanks in advance for any input.
Ric
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