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MXS-2259: Limit size of client reads

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Given the assumption that queries are rarely 16MB long and that
realistically the only time that happens is during a large dump of data,
we can limit the size of a single read to at most one MariaDB/MySQL packet
at a time. This change allows the network throttling to engage a lot
sooner and reduces the maximum overshoot of throtting to 16MB.
This commit is contained in:
Markus Mäkelä 2019-04-05 11:04:04 +03:00
parent aad29404c6
commit 05515cca16
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GPG Key ID: 72D48FCE664F7B19
3 changed files with 14 additions and 3 deletions
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1
include/maxscale/dcb.h
View File

@ -265,6 +265,7 @@ DCB* dcb_accept(DCB* listener);
DCB* dcb_alloc(dcb_role_t, struct servlistener*);
DCB* dcb_connect(struct server*, struct session*, const char*);
int dcb_read(DCB*, GWBUF**, int);
int dcb_bytes_readable(DCB* dcb);
int dcb_drain_writeq(DCB*);
void dcb_close(DCB*);

4
server/core/dcb.cc
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@ -100,7 +100,6 @@ static inline DCB* dcb_find_in_list(DCB* dcb);
static void dcb_stop_polling_and_shutdown(DCB* dcb);
static bool dcb_maybe_add_persistent(DCB*);
static inline bool dcb_write_parameter_check(DCB* dcb, GWBUF* queue);
static int dcb_bytes_readable(DCB* dcb);
static int dcb_read_no_bytes_available(DCB* dcb, int nreadtotal);
static int dcb_create_SSL(DCB* dcb, SSL_LISTENER* ssl);
static int dcb_read_SSL(DCB* dcb, GWBUF** head);
@ -638,9 +637,10 @@ int dcb_read(DCB* dcb,
* Find the number of bytes available for the DCB's socket
*
* @param dcb The DCB to read from
*
* @return -1 on error, otherwise the total number of bytes available
*/
static int dcb_bytes_readable(DCB* dcb)
int dcb_bytes_readable(DCB* dcb)
{
int bytesavailable;

12
server/modules/protocol/MySQL/mariadbclient/mysql_client.cc
View File

@ -489,7 +489,10 @@ int gw_read_client_event(DCB* dcb)
{
max_bytes = 36;
}
return_code = dcb_read(dcb, &read_buffer, max_bytes);
const uint32_t max_single_read = GW_MYSQL_MAX_PACKET_LEN + MYSQL_HEADER_LEN;
return_code = dcb_read(dcb, &read_buffer, max_bytes > 0 ? max_bytes : max_single_read);
if (return_code < 0)
{
dcb_close(dcb);
@ -499,6 +502,13 @@ int gw_read_client_event(DCB* dcb)
return return_code;
}
if (nbytes_read == max_single_read && dcb_bytes_readable(dcb) > 0)
{
// We read a maximally long packet, route it first. This is done in case there's a lot more data
// waiting and we have to start throttling the reads.
poll_fake_read_event(dcb);
}
return_code = 0;
switch (protocol->protocol_auth_state)