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Connection to postgres closed with 'This socket is closed' error message

Connection to postgres closed with 'This socket is closed' error message


I'm migrating toward node.js 0.6.12 and now got the following error messages when using pg module (version 0.6.14):

Error: This socket is closed.
at Socket._write (net.js:453:28)
at Socket.write (net.js:446:15)
at [object Object]._send (/home/luc/node_modules/pg/lib/connection.js:102:24)
at [object Object].flush (/home/luc/node_modules/pg/lib/connection.js:192:8)
at [object Object].getRows (/home/luc/node_modules/pg/lib/query.js:112:14)
at [object Object].prepare (/home/luc/node_modules/pg/lib/query.js:150:8)
at [object Object].submit (/home/luc/node_modules/pg/lib/query.js:97:10)
at [object Object]._pulseQueryQueue (/home/luc/node_modules/pg/lib/client.js:166:24)
at [object Object].query (/home/luc/node_modules/pg/lib/client.js:193:8)
at /home/luc/test/routes/user.js:23:29

The line indicated in my code is:

var get_obj = client.query("SELECT id FROM users WHERE name = $1", [name]);

This use to work fine with node 0.4.8 and gp 0.5.0 but does not work anymore now I'm testing the migration.

I saw several error like this one on the net but no answer.


This seems to be linked to the way I handle my postgres Connection. Today I create a single connection when running the app. I think creating a new connection on each request would be better. Is the best solution to have the connection created in an express middleware ?

Problem courtesy of: Luc


Normally, frameworks and middleware keep the connection open (or: a pool of connections). The problem lies most probably in your node.js code (or usage). BTW: if you have access to the postgres's logfiles, you can probably see explicit disconnections from the node.js. (log_connections and log_disconnections should both be set to True to see this)

Connect+disconnect is considered an expensive operation (TCP traffic, authorisation, forking a worker process (for postgres) , session setup, logging, (accounting?) ). But if it works for you (or you have only one request+reply for the session) it's okay.

Cost /resource usage estimates:

For the session setup:

  • TCP/IP connection setup: 2*2 IP packets := 4*round-trip delay
  • login /password:
    • 2*2 TCP readwrites := 4 * round-trip delays
    • 4 system R/W calls
    • a few database queries / lookups for user authorisation, (say 10...100 disk reads; mostly cached)
    • session construction := fork (for postgres) + lots of COW pages being cloned (? 100-1000 pagefaults?)
  • session initialisation := a few round trips

for the query:

  • send+ receive query := a few TCP/IP round-trips
  • parse := a few (1...100) catalog lookups (mostly from disk cache)
  • execute := xxx disk reads (possibly from cache)
  • fetch and store results := allocate (dirty) buffers
  • send results := xxx TCP round-trips
  • discard result-buffers := (almost for free!)

Session teardown:

  • 3*2 IP roundtrips
  • exit() of the child process, wait() for the parent process (Sorry, I think in unix-terms ;-)
  • 1 socket-descriptor in TIME_WAIT state for a few seconds / minutes

As you can see, the amount of resources spent on connection build-up is 10, maybe 100 times as big as what a typical query+result will cost; if you have more than one query to execute it will be wise to keep the connection open. (or maintain a pool of open connections)

For simplicity, I ignored CPU consumption and mainly ignored memory/buffer usage. Nowadays, CPU almost seems for free; the amount of calculation that can be done while waiting for a disk (10 ms) or network (x ms) is incredible: several (100...10K?) ticks per byte.

Solution courtesy of: wildplasser


View additional discussion.

This post first appeared on Node.js Recipes, please read the originial post: here

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Connection to postgres closed with 'This socket is closed' error message


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