日志接口
PG有新旧两种样式的接口。
新样式：
ereport(ERROR,
(errcode(ERRCODE_UNDEFINED_CURSOR),
errmsg("portal \"%s\" not found", stmt->portalname),
... other errxxx() fields as needed ...));
旧样式：
elog(ERROR, "portal \"%s\" not found", stmt->portalname);
不论新旧接口，在内部都是创建了一个stack entry保存数据：
/*
* ErrorData holds the data accumulated during any one ereport() cycle.
* Any non-NULL pointers must point to palloc'd data.
* (The const pointers are an exception; we assume they point at non-freeable
* constant strings.)
*/
typedef struct ErrorData
{
int elevel; /* error level */
bool output_to_server; /* will report to server log? */
bool output_to_client; /* will report to client? */
bool show_funcname; /* true to force funcname inclusion */
bool hide_stmt; /* true to prevent STATEMENT: inclusion */
bool hide_ctx; /* true to prevent CONTEXT: inclusion */
const char *filename; /* __FILE__ of ereport() call */
int lineno; /* __LINE__ of ereport() call */
const char *funcname; /* __func__ of ereport() call */
const char *domain; /* message domain */
const char *context_domain; /* message domain for context message */
int sqlerrcode; /* encoded ERRSTATE */
char *message; /* primary error message (translated) */
char *detail; /* detail error message */
char *detail_log; /* detail error message for server log only */
char *hint; /* hint message */
char *context; /* context message */
const char *message_id; /* primary message's id (original string) */
char *schema_name; /* name of schema */
char *table_name; /* name of table */
char *column_name; /* name of column */
char *datatype_name; /* name of datatype */
char *constraint_name; /* name of constraint */
int cursorpos; /* cursor index into query string */
int internalpos; /* cursor index into internalquery */
char *internalquery; /* text of internally-generated query */
int saved_errno; /* errno at entry */
/* context containing associated non-constant strings */
struct MemoryContextData *assoc_context;
} ErrorData;
日志级别
PG的日志级别定义如下：
/* Error level codes */
#define DEBUG5 10 /* Debugging messages, in categories of
* decreasing detail. */
#define DEBUG4 11
#define DEBUG3 12
#define DEBUG2 13
#define DEBUG1 14 /* used by GUC debug_* variables */
#define LOG 15 /* Server operational messages; sent only to
* server log by default. */
#define LOG_SERVER_ONLY 16 /* Same as LOG for server reporting, but never
* sent to client. */
#define COMMERROR LOG_SERVER_ONLY /* Client communication problems; same as
* LOG for server reporting, but never
* sent to client. */
#define INFO 17 /* Messages specifically requested by user (eg
* VACUUM VERBOSE output); always sent to
* client regardless of client_min_messages,
* but by default not sent to server log. */
#define NOTICE 18 /* Helpful messages to users about query
* operation; sent to client and not to server
* log by default. */
#define WARNING 19 /* Warnings. NOTICE is for expected messages
* like implicit sequence creation by SERIAL.
* WARNING is for unexpected messages. */
#define ERROR 20 /* user error - abort transaction; return to
* known state */
/* Save ERROR value in PGERROR so it can be restored when Win32 includes
* modify it. We have to use a constant rather than ERROR because macros
* are expanded only when referenced outside macros.
*/
#ifdef WIN32
#define PGERROR 20
#endif
#define FATAL 21 /* fatal error - abort process */
#define PANIC 22 /* take down the other backends with me */
在日志级别大于等于ERROR时，日志接口不会返回。ERROR级别时通过longjmp向上抛出，FATAL级别时进程退出，PANIC级别时进程直接abort。
同时PG可以将错误消息发送到客户端。
日志目的地
PG支持将日志写到标准输出、syslog、eventlog或者csvlog中。
/* Log destination bitmap */
#define LOG_DESTINATION_STDERR 1
#define LOG_DESTINATION_SYSLOG 2
#define LOG_DESTINATION_EVENTLOG 4
#define LOG_DESTINATION_CSVLOG 8
