Description of problem:
The client discovered this when testing with RHEL7 against a sizable groups.db file. The 'getet groups' list was truncated and was missing most entries. Florian had a look and submitted the following upstream patch which was tested to resolve the issue:

https://sourceware.org/bugzilla/show_bug.cgi?id=19837

<snip>
nss_db: No retries for some long lines with a larger buffer
_nss_db_get*ent_r returns the wrong error code if parse_line fails.  As a result, only long lines which are large enough not to fit into the caller-provided buffer result in ERANGE with NSS_STATUS_TRYAGAIN.  If parse_line detects that there is not enough room, NSS_STATUS_NOTFOUND is returned, which stops enumeration.

Patch for later reference (I will post it to libc-alpha as well):

diff --git a/nss/nss_db/db-XXX.c b/nss/nss_db/db-XXX.c
index 03c18d7..125a5e9 100644
--- a/nss/nss_db/db-XXX.c
+++ b/nss/nss_db/db-XXX.c
@@ -288,8 +288,8 @@ CONCAT(_nss_db_get,ENTNAME_r) (struct STRUCTURE *result, char *buffer,
 	    }
 	  if (err < 0)
 	    {
-	      H_ERRNO_SET (HOST_NOT_FOUND);
-	      status = NSS_STATUS_NOTFOUND;
+	      H_ERRNO_SET (NETDB_INTERNAL);
+	      status = NSS_STATUS_TRYAGAIN;
 	      break;
 	    }
</snip>

Version-Release number of selected component (if applicable):
glibc-2.17-106.el7_2.4

How reproducible:

Steps to Reproduce:
1.Have long "group" entries (many users/group) and generate/use NSS_db in nsswitch.

2. List group with "getent group"
3. Note that the listing is truncated

I can't include the client's db file unfortunately that we were using for replication, but this patch was tested and corrected the client issue.