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Commit721f7bd

Browse files
committed
libpq: Add target_session_attrs parameter.
Commit274bb2b made it possible tospecify multiple IPs in a connection string, but that's not goodenough for the case where you have a read-write master and a bunch ofread-only standbys and want to connect to whichever server is themaster at the current time. This commit allows that, by making itpossible to specify target_session_attrs=read-write as a connectionparameter.There was extensive discussion of the best name for the connectionparameter and its values as well as the best way to distinguish masterand standbys. For now, adopt the same solution as JDBC: if the userwants a read-write connection, issue 'show transaction_read_only' andrejection the connection if the result is 'on'. In the future, wecould add additional values of this new target_session_attrs parameterthat issue different queries; or we might have some way ofdistinguishing the server type without resorting to an SQL query; butright now, we have this, and that's (hopefully) a good start.Victor Wagner and Mithun Cy. Design review by Álvaro Herrera, CatalinIacob, Takayuki Tsunakawa, and Craig Ringer; code review by me. Ichanged Mithun's patch to skip all remaining IPs for a host if wereject a connection based on this new parameter, rewrote thedocumentation, and did some other cosmetic cleanup.Discussion:http://postgr.es/m/CAD__OuhqPRGpcsfwPHz_PDqAGkoqS1UvnUnOnAB-LBWBW=wu4A@mail.gmail.com
1 parent4fafa57 commit721f7bd

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4 files changed

+227
-51
lines changed

4 files changed

+227
-51
lines changed

‎doc/src/sgml/libpq.sgml

Lines changed: 28 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -811,7 +811,7 @@ postgresql://localhost/mydb
811811
postgresql://user@localhost
812812
postgresql://user:secret@localhost
813813
postgresql://other@localhost/otherdb?connect_timeout=10&application_name=myapp
814-
postgresql://host1:123,host2:456/somedb
814+
postgresql://host1:123,host2:456/somedb?target_session_attrs=any&application_name=myapp
815815
</programlisting>
816816
Components of the hierarchical part of the <acronym>URI</acronym> can also
817817
be given as parameters. For example:
@@ -1386,6 +1386,23 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
13861386
</para>
13871387
</listitem>
13881388
</varlistentry>
1389+
1390+
<varlistentry id="libpq-connect-target-session-attrs" xreflabel="target_session_attrs">
1391+
<term><literal>target_session_attrs</literal></term>
1392+
<listitem>
1393+
<para>
1394+
If this parameter is set to <literal>read-write</literal>, only a
1395+
connection in which read-write transactions are accepted by default
1396+
is considered acceptable. The query
1397+
<literal>show transaction_read_only</literal> will be sent upon any
1398+
successful connection; if it returns <literal>on</>, the connection
1399+
will be closed. If multiple hosts were specified in the connection
1400+
string, any remaining servers will be tried just as if the connection
1401+
attempt had failed. The default value of this parameter,
1402+
<literal>any</>, regards all connections as acceptable.
1403+
</para>
1404+
</listitem>
1405+
</varlistentry>
13891406
</variablelist>
13901407
</para>
13911408
</sect2>
@@ -7069,6 +7086,16 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
70697086
linkend="libpq-connect-client-encoding"> connection parameter.
70707087
</para>
70717088
</listitem>
7089+
7090+
<listitem>
7091+
<para>
7092+
<indexterm>
7093+
<primary><envar>PGTARGETSESSIONATTRS</envar></primary>
7094+
</indexterm>
7095+
<envar>PGTARGETSESSIONATTRS</envar> behaves the same as the <xref
7096+
linkend="libpq-connect-target-session-attrs"> connection parameter.
7097+
</para>
7098+
</listitem>
70727099
</itemizedlist>
70737100
</para>
70747101

‎src/interfaces/libpq/fe-connect.c

Lines changed: 193 additions & 49 deletions
Original file line numberDiff line numberDiff line change
@@ -108,6 +108,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
108108
#defineDefaultOption""
109109
#defineDefaultAuthtype ""
110110
#defineDefaultPassword ""
111+
#defineDefaultTargetSessionAttrs"any"
111112
#ifdefUSE_SSL
112113
#defineDefaultSSLMode "prefer"
113114
#else
@@ -300,6 +301,11 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
300301
"Replication","D",5,
301302
offsetof(structpg_conn,replication)},
302303

304+
{"target_session_attrs","PGTARGETSESSIONATTRS",
305+
DefaultTargetSessionAttrs,NULL,
306+
"Target-Session-Attrs","",11,/* sizeof("read-write") = 11 */
307+
offsetof(structpg_conn,target_session_attrs)},
308+
303309
/* Terminating entry --- MUST BE LAST */
304310
{NULL,NULL,NULL,NULL,
305311
NULL,NULL,0}
@@ -336,6 +342,8 @@ static PGconn *makeEmptyPGconn(void);
336342
staticboolfillPGconn(PGconn*conn,PQconninfoOption*connOptions);
337343
staticvoidfreePGconn(PGconn*conn);
338344
staticvoidclosePGconn(PGconn*conn);
345+
staticvoidrelease_all_addrinfo(PGconn*conn);
346+
staticvoidsendTerminateConn(PGconn*conn);
339347
staticPQconninfoOption*conninfo_init(PQExpBuffererrorMessage);
340348
staticPQconninfoOption*parse_connection_string(constchar*conninfo,
341349
PQExpBuffererrorMessage,booluse_defaults);
@@ -1025,6 +1033,22 @@ connectOptions2(PGconn *conn)
10251033
gotooom_error;
10261034
}
10271035

1036+
/*
1037+
* Validate target_session_attrs option.
1038+
*/
1039+
if (conn->target_session_attrs)
1040+
{
1041+
if (strcmp(conn->target_session_attrs,"any")!=0
1042+
&&strcmp(conn->target_session_attrs,"read-write")!=0)
1043+
{
1044+
conn->status=CONNECTION_BAD;
1045+
printfPQExpBuffer(&conn->errorMessage,
1046+
libpq_gettext("invalid target_session_attrs value: \"%s\"\n"),
1047+
conn->target_session_attrs);
1048+
return false;
1049+
}
1050+
}
1051+
10281052
/*
10291053
* Only if we get this far is it appropriate to try to connect. (We need a
10301054
* state flag, rather than just the boolean result of this function, in
@@ -1814,6 +1838,7 @@ PQconnectPoll(PGconn *conn)
18141838
/* Special cases: proceed without waiting. */
18151839
caseCONNECTION_SSL_STARTUP:
18161840
caseCONNECTION_NEEDED:
1841+
caseCONNECTION_CHECK_WRITABLE:
18171842
break;
18181843

18191844
default:
@@ -2752,27 +2777,6 @@ PQconnectPoll(PGconn *conn)
27522777
gotoerror_return;
27532778
}
27542779

2755-
/* We can release the address lists now. */
2756-
if (conn->connhost!=NULL)
2757-
{
2758-
inti;
2759-
2760-
for (i=0;i<conn->nconnhost;++i)
2761-
{
2762-
intfamily=AF_UNSPEC;
2763-
2764-
#ifdefHAVE_UNIX_SOCKETS
2765-
if (conn->connhost[i].type==CHT_UNIX_SOCKET)
2766-
family=AF_UNIX;
2767-
#endif
2768-
2769-
pg_freeaddrinfo_all(family,
2770-
conn->connhost[i].addrlist);
2771-
conn->connhost[i].addrlist=NULL;
2772-
}
2773-
}
2774-
conn->addr_cur=NULL;
2775-
27762780
/* Fire up post-connection housekeeping if needed */
27772781
if (PG_PROTOCOL_MAJOR(conn->pversion)<3)
27782782
{
@@ -2782,7 +2786,24 @@ PQconnectPoll(PGconn *conn)
27822786
returnPGRES_POLLING_WRITING;
27832787
}
27842788

2785-
/* Otherwise, we are open for business! */
2789+
/*
2790+
* If a read-write connection is required, see if we have one.
2791+
*/
2792+
if (conn->target_session_attrs!=NULL&&
2793+
strcmp(conn->target_session_attrs,"read-write")==0)
2794+
{
2795+
conn->status=CONNECTION_OK;
2796+
if (!PQsendQuery(conn,
2797+
"show transaction_read_only"))
2798+
gotoerror_return;
2799+
conn->status=CONNECTION_CHECK_WRITABLE;
2800+
returnPGRES_POLLING_READING;
2801+
}
2802+
2803+
/* We can release the address lists now. */
2804+
release_all_addrinfo(conn);
2805+
2806+
/* We are open for business! */
27862807
conn->status=CONNECTION_OK;
27872808
returnPGRES_POLLING_OK;
27882809
}
@@ -2814,10 +2835,109 @@ PQconnectPoll(PGconn *conn)
28142835
gotoerror_return;
28152836
}
28162837

2838+
/*
2839+
* If a read-write connection is requisted check for same.
2840+
*/
2841+
if (conn->target_session_attrs!=NULL&&
2842+
strcmp(conn->target_session_attrs,"read-write")==0)
2843+
{
2844+
conn->status=CONNECTION_OK;
2845+
if (!PQsendQuery(conn,
2846+
"show transaction_read_only"))
2847+
gotoerror_return;
2848+
conn->status=CONNECTION_CHECK_WRITABLE;
2849+
returnPGRES_POLLING_READING;
2850+
}
2851+
2852+
/* We can release the address lists now. */
2853+
release_all_addrinfo(conn);
2854+
28172855
/* We are open for business! */
28182856
conn->status=CONNECTION_OK;
28192857
returnPGRES_POLLING_OK;
28202858

2859+
caseCONNECTION_CHECK_WRITABLE:
2860+
{
2861+
conn->status=CONNECTION_OK;
2862+
if (!PQconsumeInput(conn))
2863+
gotoerror_return;
2864+
2865+
if (PQisBusy(conn))
2866+
{
2867+
conn->status=CONNECTION_CHECK_WRITABLE;
2868+
returnPGRES_POLLING_READING;
2869+
}
2870+
2871+
res=PQgetResult(conn);
2872+
if (res&& (PQresultStatus(res)==PGRES_TUPLES_OK)&&
2873+
PQntuples(res)==1)
2874+
{
2875+
char*val;
2876+
2877+
val=PQgetvalue(res,0,0);
2878+
if (strncmp(val,"on",2)==0)
2879+
{
2880+
PQclear(res);
2881+
2882+
/* Not writable; close connection. */
2883+
appendPQExpBuffer(&conn->errorMessage,
2884+
libpq_gettext("could not make a writable "
2885+
"connection to server "
2886+
"\"%s:%s\"\n"),
2887+
conn->connhost[conn->whichhost].host,
2888+
conn->connhost[conn->whichhost].port);
2889+
conn->status=CONNECTION_OK;
2890+
sendTerminateConn(conn);
2891+
pqDropConnection(conn, true);
2892+
2893+
/* Skip any remaining addresses for this host. */
2894+
conn->addr_cur=NULL;
2895+
if (conn->whichhost+1<conn->nconnhost)
2896+
{
2897+
conn->status=CONNECTION_NEEDED;
2898+
gotokeep_going;
2899+
}
2900+
2901+
/* No more addresses to try. So we fail. */
2902+
gotoerror_return;
2903+
}
2904+
PQclear(res);
2905+
2906+
/* We can release the address lists now. */
2907+
release_all_addrinfo(conn);
2908+
2909+
/* We are open for business! */
2910+
conn->status=CONNECTION_OK;
2911+
returnPGRES_POLLING_OK;
2912+
}
2913+
2914+
/*
2915+
* Something went wrong with "show transaction_read_only". We
2916+
* should try next addresses.
2917+
*/
2918+
if (res)
2919+
PQclear(res);
2920+
appendPQExpBuffer(&conn->errorMessage,
2921+
libpq_gettext("test \"show transaction_read_only\" failed "
2922+
" on \"%s:%s\" \n"),
2923+
conn->connhost[conn->whichhost].host,
2924+
conn->connhost[conn->whichhost].port);
2925+
conn->status=CONNECTION_OK;
2926+
sendTerminateConn(conn);
2927+
pqDropConnection(conn, true);
2928+
2929+
if (conn->addr_cur->ai_next!=NULL||
2930+
conn->whichhost+1<conn->nconnhost)
2931+
{
2932+
conn->addr_cur=conn->addr_cur->ai_next;
2933+
conn->status=CONNECTION_NEEDED;
2934+
gotokeep_going;
2935+
}
2936+
2937+
/* No more addresses to try. So we fail. */
2938+
gotoerror_return;
2939+
}
2940+
28212941
default:
28222942
appendPQExpBuffer(&conn->errorMessage,
28232943
libpq_gettext("invalid connection state %d, "
@@ -3109,6 +3229,8 @@ freePGconn(PGconn *conn)
31093229
free(conn->outBuffer);
31103230
if (conn->rowBuf)
31113231
free(conn->rowBuf);
3232+
if (conn->target_session_attrs)
3233+
free(conn->target_session_attrs);
31123234
termPQExpBuffer(&conn->errorMessage);
31133235
termPQExpBuffer(&conn->workBuffer);
31143236

@@ -3120,19 +3242,41 @@ freePGconn(PGconn *conn)
31203242
}
31213243

31223244
/*
3123-
* closePGconn
3124-
* - properly close a connection to the backend
3125-
*
3126-
* This should reset or release all transient state, but NOT the connection
3127-
* parameters. On exit, the PGconn should be in condition to start a fresh
3128-
* connection with the same parameters (see PQreset()).
3245+
* release_all_addrinfo
3246+
* - free addrinfo of all hostconn elements.
31293247
*/
3248+
31303249
staticvoid
3131-
closePGconn(PGconn*conn)
3250+
release_all_addrinfo(PGconn*conn)
31323251
{
3133-
PGnotify*notify;
3134-
pgParameterStatus*pstatus;
3252+
if (conn->connhost!=NULL)
3253+
{
3254+
inti;
3255+
3256+
for (i=0;i<conn->nconnhost;++i)
3257+
{
3258+
intfamily=AF_UNSPEC;
3259+
3260+
#ifdefHAVE_UNIX_SOCKETS
3261+
if (conn->connhost[i].type==CHT_UNIX_SOCKET)
3262+
family=AF_UNIX;
3263+
#endif
31353264

3265+
pg_freeaddrinfo_all(family,
3266+
conn->connhost[i].addrlist);
3267+
conn->connhost[i].addrlist=NULL;
3268+
}
3269+
}
3270+
conn->addr_cur=NULL;
3271+
}
3272+
3273+
/*
3274+
* sendTerminateConn
3275+
* - Send a terminate message to backend.
3276+
*/
3277+
staticvoid
3278+
sendTerminateConn(PGconn*conn)
3279+
{
31363280
/*
31373281
* Note that the protocol doesn't allow us to send Terminate messages
31383282
* during the startup phase.
@@ -3147,6 +3291,23 @@ closePGconn(PGconn *conn)
31473291
pqPutMsgEnd(conn);
31483292
(void)pqFlush(conn);
31493293
}
3294+
}
3295+
3296+
/*
3297+
* closePGconn
3298+
* - properly close a connection to the backend
3299+
*
3300+
* This should reset or release all transient state, but NOT the connection
3301+
* parameters. On exit, the PGconn should be in condition to start a fresh
3302+
* connection with the same parameters (see PQreset()).
3303+
*/
3304+
staticvoid
3305+
closePGconn(PGconn*conn)
3306+
{
3307+
PGnotify*notify;
3308+
pgParameterStatus*pstatus;
3309+
3310+
sendTerminateConn(conn);
31503311

31513312
/*
31523313
* Must reset the blocking status so a possible reconnect will work.
@@ -3165,25 +3326,8 @@ closePGconn(PGconn *conn)
31653326
conn->asyncStatus=PGASYNC_IDLE;
31663327
pqClearAsyncResult(conn);/* deallocate result */
31673328
resetPQExpBuffer(&conn->errorMessage);
3168-
if (conn->connhost!=NULL)
3169-
{
3170-
inti;
3171-
3172-
for (i=0;i<conn->nconnhost;++i)
3173-
{
3174-
intfamily=AF_UNSPEC;
3175-
3176-
#ifdefHAVE_UNIX_SOCKETS
3177-
if (conn->connhost[i].type==CHT_UNIX_SOCKET)
3178-
family=AF_UNIX;
3179-
#endif
3329+
release_all_addrinfo(conn);
31803330

3181-
pg_freeaddrinfo_all(family,
3182-
conn->connhost[i].addrlist);
3183-
conn->connhost[i].addrlist=NULL;
3184-
}
3185-
}
3186-
conn->addr_cur=NULL;
31873331
notify=conn->notifyHead;
31883332
while (notify!=NULL)
31893333
{

‎src/interfaces/libpq/libpq-fe.h

Lines changed: 3 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -62,7 +62,9 @@ typedef enum
6262
* backend startup. */
6363
CONNECTION_SETENV,/* Negotiating environment. */
6464
CONNECTION_SSL_STARTUP,/* Negotiating SSL. */
65-
CONNECTION_NEEDED/* Internal state: connect() needed */
65+
CONNECTION_NEEDED,/* Internal state: connect() needed */
66+
CONNECTION_CHECK_WRITABLE/* Check if we could make a writable
67+
* connection. */
6668
}ConnStatusType;
6769

6870
typedefenum

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