记录PG的一次内存泄漏

问题

使用cast函数误将时间字符串携带了多余字母，导致获取的最终时间结果的时间“抹掉了”。

时间“消失”了

进一步修改时间字符串

发现报错time zone xxx。系统误将时间字符串当成了time zone 时区。通过分析源码可知pg的时区是缓存在上下文中Timezones，且没有回收机制。

pg_tz *
pg_tzset(const char *tzname)
{
	pg_tz_cache *tzp;
	struct state tzstate;
	char		uppername[TZ_STRLEN_MAX + 1];
	char		canonname[TZ_STRLEN_MAX + 1];
	char	   *p;

	if (strlen(tzname) > TZ_STRLEN_MAX)
		return NULL;			/* not going to fit */

	if (!timezone_cache)
		if (!init_timezone_hashtable())
			return NULL;

	/*
	 * Upcase the given name to perform a case-insensitive hashtable search.
	 * (We could alternatively downcase it, but we prefer upcase so that we
	 * can get consistently upcased results from tzparse() in case the name is
	 * a POSIX-style timezone spec.)
	 */
	p = uppername;
	while (*tzname)
		*p++ = pg_toupper((unsigned char) *tzname++);
	*p = '\0';

	tzp = (pg_tz_cache *) hash_search(timezone_cache,
									  uppername,
									  HASH_FIND,
									  NULL);
	if (tzp)
	{
		/* Timezone found in cache, nothing more to do */
		return &tzp->tz;
	}

	/*
	 * "GMT" is always sent to tzparse(), as per discussion above.
	 */
	if (strcmp(uppername, "GMT") == 0)
	{
		if (!tzparse(uppername, &tzstate, true))
		{
			/* This really, really should not happen ... */
			elog(ERROR, "could not initialize GMT time zone");
		}
		/* Use uppercase name as canonical */
		strcpy(canonname, uppername);
	}
	else if (tzload(uppername, canonname, &tzstate, true) != 0)
	{
		if (uppername[0] == ':' || !tzparse(uppername, &tzstate, false))
		{
			/* Unknown timezone. Fail our call instead of loading GMT! */
			return NULL;
		}
		/* For POSIX timezone specs, use uppercase name as canonical */
		strcpy(canonname, uppername);
	}

	/* Save timezone in the cache */
	tzp = (pg_tz_cache *) hash_search(timezone_cache,
									  uppername,
									  HASH_ENTER,
									  NULL);

	/* hash_search already copied uppername into the hash key */
	strcpy(tzp->tz.TZname, canonname);
	memcpy(&tzp->tz.state, &tzstate, sizeof(tzstate));

	return &tzp->tz;
}


static bool
init_timezone_hashtable(void)
{
	HASHCTL		hash_ctl;

	hash_ctl.keysize = TZ_STRLEN_MAX + 1;
	hash_ctl.entrysize = sizeof(pg_tz_cache);

	timezone_cache = hash_create("Timezones",
								 4,
								 &hash_ctl,
								 HASH_ELEM | HASH_STRINGS);
	if (!timezone_cache)
		return false;

	return true;
}

pg的所有时区存储在表pg_timezone_names中。生成时区上下文时没有做校验，所以遇到新的时间点就会创建新的Timezone上下文，造成内存的泄漏。

• 调用堆栈