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postgres_fdw: Remove redundancy in postgresAcquireSampleRowsFunc().

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Previously, in the loop in postgresAcquireSampleRowsFunc() to iterate
fetching rows from a given remote table, we redundantly 1) determined the
fetch size by parsing the table's server/table-level options and then 2)
constructed the fetch command; remove that redundancy.

Author: Etsuro Fujita
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/CAPmGK17_urk9qkLV65_iYMFw64z5qhdfhY=tMVV6Jg4KNYx8+w@mail.gmail.com
This commit is contained in:
Etsuro Fujita 2019-07-03 17:51:00 +09:00
parent e72489e101
commit 2a1612104c
1 changed files with 34 additions and 29 deletions
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41
contrib/postgres_fdw/postgres_fdw.c
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@ -4490,31 +4490,20 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
/* In what follows, do not risk leaking any PGresults. */ /* In what follows, do not risk leaking any PGresults. */
PG_TRY(); PG_TRY();
{ {
char fetch_sql[64];
int fetch_size;
ListCell *lc;
res = pgfdw_exec_query(conn, sql.data); res = pgfdw_exec_query(conn, sql.data);
if (PQresultStatus(res) != PGRES_COMMAND_OK) if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, conn, false, sql.data); pgfdw_report_error(ERROR, res, conn, false, sql.data);
PQclear(res); PQclear(res);
res = NULL; res = NULL;
/* Retrieve and process rows a batch at a time. */
for (;;)
{
char fetch_sql[64];
int fetch_size;
int numrows;
int i;
ListCell *lc;
/* Allow users to cancel long query */
CHECK_FOR_INTERRUPTS();
/* /*
* XXX possible future improvement: if rowstoskip is large, we * Determine the fetch size. The default is arbitrary, but shouldn't
* could issue a MOVE rather than physically fetching the rows, * be enormous.
* then just adjust rowstoskip and samplerows appropriately.
*/ */
/* The fetch size is arbitrary, but shouldn't be enormous. */
fetch_size = 100; fetch_size = 100;
foreach(lc, server->options) foreach(lc, server->options)
{ {
@ -4537,10 +4526,26 @@ postgresAcquireSampleRowsFunc(Relation relation, int elevel,
} }
} }
/* Fetch some rows */ /* Construct command to fetch rows from remote. */
snprintf(fetch_sql, sizeof(fetch_sql), "FETCH %d FROM c%u", snprintf(fetch_sql, sizeof(fetch_sql), "FETCH %d FROM c%u",
fetch_size, cursor_number); fetch_size, cursor_number);
/* Retrieve and process rows a batch at a time. */
for (;;)
{
int numrows;
int i;
/* Allow users to cancel long query */
CHECK_FOR_INTERRUPTS();
/*
* XXX possible future improvement: if rowstoskip is large, we
* could issue a MOVE rather than physically fetching the rows,
* then just adjust rowstoskip and samplerows appropriately.
*/
/* Fetch some rows */
res = pgfdw_exec_query(conn, fetch_sql); res = pgfdw_exec_query(conn, fetch_sql);
/* On error, report the original query, not the FETCH. */ /* On error, report the original query, not the FETCH. */
if (PQresultStatus(res) != PGRES_TUPLES_OK) if (PQresultStatus(res) != PGRES_TUPLES_OK)