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Extend the abilities of libpq's target_session_attrs parameter.

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In addition to the existing options of "any" and "read-write", we
now support "read-only", "primary", "standby", and "prefer-standby".
"read-write" retains its previous meaning of "transactions are
read-write by default", and "read-only" inverts that.  The other
three modes test specifically for hot-standby status, which is not
quite the same thing.  (Setting default_transaction_read_only on
a primary server renders it read-only to this logic, but not a
standby.)

Furthermore, if talking to a v14 or later server, no extra network
round trip is needed to detect the session's status; the GUC_REPORT
variables delivered by the server are enough.  When talking to an
older server, a SHOW or SELECT query is issued to detect session
read-only-ness or server hot-standby state, as needed.

Haribabu Kommi, Greg Nancarrow, Vignesh C, Tom Lane; reviewed at
various times by Laurenz Albe, Takayuki Tsunakawa, Peter Smith.

Discussion: https://postgr.es/m/CAF3+xM+8-ztOkaV9gHiJ3wfgENTq97QcjXQt+rbFQ6F7oNzt9A@mail.gmail.com
This commit is contained in:
Tom Lane
2021-03-02 20:17:45 -05:00
parent 57e6db706e
commit ee28cacf61
6 changed files with 463 additions and 121 deletions
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27
src/interfaces/libpq/libpq-int.h
View File

@@ -232,6 +232,26 @@ typedef enum
PGQUERY_DESCRIBE /* Describe Statement or Portal */
} PGQueryClass;
/* Target server type (decoded value of target_session_attrs) */
typedef enum
{
SERVER_TYPE_ANY = 0, /* Any server (default) */
SERVER_TYPE_READ_WRITE, /* Read-write server */
SERVER_TYPE_READ_ONLY, /* Read-only server */
SERVER_TYPE_PRIMARY, /* Primary server */
SERVER_TYPE_STANDBY, /* Standby server */
SERVER_TYPE_PREFER_STANDBY, /* Prefer standby server */
SERVER_TYPE_PREFER_STANDBY_PASS2 /* second pass - behaves same as ANY */
} PGTargetServerType;
/* Boolean value plus a not-known state, for GUCs we might have to fetch */
typedef enum
{
PG_BOOL_UNKNOWN = 0, /* Currently unknown */
PG_BOOL_YES, /* Yes (true) */
PG_BOOL_NO /* No (false) */
} PGTernaryBool;
/* PGSetenvStatusType defines the state of the pqSetenv state machine */
/* (this is used only for 2.0-protocol connections) */
@@ -370,9 +390,7 @@ struct pg_conn
* "sspi") */
char *ssl_min_protocol_version; /* minimum TLS protocol version */
char *ssl_max_protocol_version; /* maximum TLS protocol version */
/* Type of connection to make. Possible values: any, read-write. */
char *target_session_attrs;
char *target_session_attrs; /* desired session properties */
/* Optional file to write trace info to */
FILE *Pfdebug;
@@ -422,6 +440,7 @@ struct pg_conn
char *write_err_msg; /* write error message, or NULL if OOM */
/* Transient state needed while establishing connection */
PGTargetServerType target_server_type; /* desired session properties */
bool try_next_addr; /* time to advance to next address/host? */
bool try_next_host; /* time to advance to next connhost[]? */
struct addrinfo *addrlist; /* list of addresses for current connhost */
@@ -437,6 +456,8 @@ struct pg_conn
pgParameterStatus *pstatus; /* ParameterStatus data */
int client_encoding; /* encoding id */
bool std_strings; /* standard_conforming_strings */
PGTernaryBool default_transaction_read_only; /* default_transaction_read_only */
PGTernaryBool in_hot_standby; /* in_hot_standby */
PGVerbosity verbosity; /* error/notice message verbosity */
PGContextVisibility show_context; /* whether to show CONTEXT field */
PGlobjfuncs *lobjfuncs; /* private state for large-object access fns */