Fast Array Inserts with Postgres - postgresql

Question

In Oracle OCI and OCCI there are API facilities to perform array inserts where you build up an array of values in the client and send this array along with a prepared statement to the server to insert thousands of entries into a table in a single shot resulting in huge performance improvements in some scenarios. Is there anything similar in PostgreSQL ?
I am using the stock PostgreSQL C API.
Some pseudo code to illustrate what i have in mind:
stmt = con->prepare("INSERT INTO mytable VALUES ($1, $2, $3)");
pg_c_api_array arr(stmt);
for triplet(a, b, c) in mylongarray:
pg_c_api_variant var = arr.add();
var.bind(1, a);
var.bind(2, b);
var.bind(3, c);
stmt->bindarray(arr);
stmt->exec()

Answer 1

PostgreSQL has similar functionality - statement COPY and COPY API - it is very fast
libpq documentation
char *data = "10\t20\40\n20\t30\t40";
pres = PQexec(pconn, "COPY mytable FROM stdin");
/* can be call repeatedly */
copy_result = PQputCopyData(pconn, data, sizeof(data));
if (copy_result != 1)
{
fprintf(stderr, "Copy to target table failed: %s\n",
PQerrorMessage(pconn));
EXIT;
}
if (PQputCopyEnd(pconn, NULL) == -1)
{
fprintf(stderr, "Copy to target table failed: %s\n",
PQerrorMessage(pconn));
EXIT;
}
pres = PQgetResult(pconn);
if (PQresultStatus(pres) != PGRES_COMMAND_OK)
{
fprintf(stderr, "Copy to target table failed:%s\n",
PQerrorMessage(pconn));
EXIT;
}
PQclear(pres);

Answer 2

As Pavel Stehule points out, there is the COPY command and, when using libpq in C, associated functions for transmitted the copy data. I haven't used these. I mostly program against PostgreSQL in Python, have have used similar functionality from psycopg2. It's extremely simple:
conn = psycopg2.connect(CONN_STR)
cursor = conn.cursor()
f = open('data.tsv')
cusor.copy_from(f, 'incoming')
f.close()
In fact I've often replaced open with a file-like wrapper object that performs some basic data cleaning first. It's pretty seamless.

Answer 3

I like this way of creating thousands of rows in a single command:
INSERT INTO mytable VALUES (UNNEST($1), UNNEST($2), UNNEST($3));
Bind an array of the values of column 1 to $1, an array of the values of column 2 to $2 etc.! Providing the values in columns may seem a bit strange at first when you are used to thinking in rows.
You need PostgreSQL >= 8.4 for UNNEST or your own function to convert arrays into sets.