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Add a "row processor" API to libpq for better handling of large results.

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Traditionally libpq has collected an entire query result before passing
it back to the application.  That provides a simple and transactional API,
but it's pretty inefficient for large result sets.  This patch allows the
application to process each row on-the-fly instead of accumulating the
rows into the PGresult.  Error recovery becomes a bit more complex, but
often that tradeoff is well worth making.

Kyotaro Horiguchi, reviewed by Marko Kreen and Tom Lane
This commit is contained in:
Tom Lane
2012-04-04 18:27:56 -04:00
parent cb917e1544
commit 92785dac2e
10 changed files with 994 additions and 204 deletions
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12
src/interfaces/libpq/fe-connect.c
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@ -2425,7 +2425,7 @@ keep_going: /* We will come back to here until there is
conn->status = CONNECTION_AUTH_OK;
/*
* Set asyncStatus so that PQsetResult will think that
* Set asyncStatus so that PQgetResult will think that
* what comes back next is the result of a query. See
* below.
*/
@ -2686,8 +2686,11 @@ makeEmptyPGconn(void)
/* Zero all pointers and booleans */
MemSet(conn, 0, sizeof(PGconn));
/* install default row processor and notice hooks */
PQsetRowProcessor(conn, NULL, NULL);
conn->noticeHooks.noticeRec = defaultNoticeReceiver;
conn->noticeHooks.noticeProc = defaultNoticeProcessor;
conn->status = CONNECTION_BAD;
conn->asyncStatus = PGASYNC_IDLE;
conn->xactStatus = PQTRANS_IDLE;
@ -2721,11 +2724,14 @@ makeEmptyPGconn(void)
conn->inBuffer = (char *) malloc(conn->inBufSize);
conn->outBufSize = 16 * 1024;
conn->outBuffer = (char *) malloc(conn->outBufSize);
conn->rowBufLen = 32;
conn->rowBuf = (PGdataValue *) malloc(conn->rowBufLen * sizeof(PGdataValue));
initPQExpBuffer(&conn->errorMessage);
initPQExpBuffer(&conn->workBuffer);
if (conn->inBuffer == NULL ||
conn->outBuffer == NULL ||
conn->rowBuf == NULL ||
PQExpBufferBroken(&conn->errorMessage) ||
PQExpBufferBroken(&conn->workBuffer))
{
@ -2829,6 +2835,8 @@ freePGconn(PGconn *conn)
free(conn->inBuffer);
if (conn->outBuffer)
free(conn->outBuffer);
if (conn->rowBuf)
free(conn->rowBuf);
termPQExpBuffer(&conn->errorMessage);
termPQExpBuffer(&conn->workBuffer);
@ -2888,7 +2896,7 @@ closePGconn(PGconn *conn)
conn->status = CONNECTION_BAD; /* Well, not really _bad_ - just
* absent */
conn->asyncStatus = PGASYNC_IDLE;
pqClearAsyncResult(conn); /* deallocate result and curTuple */
pqClearAsyncResult(conn); /* deallocate result */
pg_freeaddrinfo_all(conn->addrlist_family, conn->addrlist);
conn->addrlist = NULL;
conn->addr_cur = NULL;