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Commite0db288

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Fix libpq's implementation of per-host connection timeouts.
Commit5f374fe attempted to turn the connect_timeout from an overallmaximum time limit into a per-host limit, but it didn't do a great job ofthat. The timer would only get restarted if we actually detected timeoutwithin connectDBComplete(), not if we changed our attention to a new hostfor some other reason. In that case the old timeout continued to run,possibly causing a premature timeout failure for the new host.Fix that, and also tweak the logic so that if we do get a timeout,we advance to the next available IP address, not to the next host name.There doesn't seem to be a good reason to assume that all the IPaddresses supplied for a given host name will necessarily fail thesame way as the current one. Moreover, this conforms better to theadmittedly-vague documentation statement that the timeout is "perconnection attempt". I changed that to "per host name or IP address"to be clearer. (Note that reconnections to the same server, such as forswitching protocol version or SSL status, don't get their own separatetimeout; that was true before and remains so.)Also clarify documentation about the interpretation of connect_timeoutvalues less than 2.This seems like a bug, so back-patch to v10 where this logic came in.Tom Lane, reviewed by Fabien CoelhoDiscussion:https://postgr.es/m/5735.1533828184@sss.pgh.pa.us
1 parent32b16d4 commite0db288

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2 files changed

+28
-18
lines changed

2 files changed

+28
-18
lines changed

‎doc/src/sgml/libpq.sgml

Lines changed: 6 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1110,11 +1110,12 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
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<term><literal>connect_timeout</literal></term>
11111111
<listitem>
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<para>
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Maximum wait for connection, in seconds (write as a decimal integer
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string). Zero or not specified means wait indefinitely. It is not
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recommended to use a timeout of less than 2 seconds.
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This timeout applies separately to each connection attempt.
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For example, if you specify two hosts and <literal>connect_timeout</>
1113+
Maximum wait for connection, in seconds (write as a decimal integer,
1114+
e.g. <literal>10</literal>). Zero, negative, or not specified means
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wait indefinitely. The minimum allowed timeout is 2 seconds, therefore
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a value of <literal>1</literal> is interpreted as <literal>2</literal>.
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This timeout applies separately to each host name or IP address.
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For example, if you specify two hosts and <literal>connect_timeout</literal>
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is 5, each host will time out if no connection is made within 5
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seconds, so the total time spent waiting for a connection might be
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up to 10 seconds.

‎src/interfaces/libpq/fe-connect.c

Lines changed: 22 additions & 13 deletions
Original file line numberDiff line numberDiff line change
@@ -1904,6 +1904,8 @@ connectDBComplete(PGconn *conn)
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PostgresPollingStatusTypeflag=PGRES_POLLING_WRITING;
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time_tfinish_time= ((time_t)-1);
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inttimeout=0;
1907+
intlast_whichhost=-2;/* certainly different from whichhost */
1908+
structaddrinfo*last_addr_cur=NULL;
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if (conn==NULL||conn->status==CONNECTION_BAD)
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return0;
@@ -1917,19 +1919,34 @@ connectDBComplete(PGconn *conn)
19171919
if (timeout>0)
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{
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/*
1920-
* Rounding could cause connection to fail; need at least 2 secs
1922+
* Rounding could cause connection to fail unexpectedly quickly;
1923+
* to prevent possibly waiting hardly-at-all, insist on at least
1924+
* two seconds.
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*/
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if (timeout<2)
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timeout=2;
1924-
/* calculate the finish time based on start + timeout */
1925-
finish_time=time(NULL)+timeout;
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}
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}
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for (;;)
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{
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intret=0;
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1935+
/*
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* (Re)start the connect_timeout timer if it's active and we are
1937+
* considering a different host than we were last time through. If
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* we've already succeeded, though, needn't recalculate.
1939+
*/
1940+
if (flag!=PGRES_POLLING_OK&&
1941+
timeout>0&&
1942+
(conn->whichhost!=last_whichhost||
1943+
conn->addr_cur!=last_addr_cur))
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{
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finish_time=time(NULL)+timeout;
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last_whichhost=conn->whichhost;
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last_addr_cur=conn->addr_cur;
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}
1949+
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/*
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* Wait, if necessary. Note that the initial state (just after
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* PQconnectStart) is to wait for the socket to select for writing.
@@ -1974,18 +1991,10 @@ connectDBComplete(PGconn *conn)
19741991
if (ret==1)/* connect_timeout elapsed */
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{
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/*
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* Attempt connection to the next host, ignoring any remaining
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* addresses for the current host.
1994+
* Give up on current server/address, try the next one.
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*/
1980-
conn->try_next_addr= false;
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conn->try_next_host= true;
1996+
conn->try_next_addr= true;
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conn->status=CONNECTION_NEEDED;
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/*
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* Restart the connect_timeout timer for the new host.
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*/
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if (timeout>0)
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finish_time=time(NULL)+timeout;
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}
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/*

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