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PG-585: pg_stat_monitor: Add code comments to the DSA related funcs.. (#360)

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Adding code comments for the DSA related functionality.
This commit is contained in:
Muhammad Usama
2023-01-23 14:36:23 +05:00
committed by GitHub
parent dfd41519cf
commit 5648b99eee
3 changed files with 92 additions and 19 deletions
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59
pg_stat_monitor.h
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@@ -107,6 +107,19 @@
/* Update this if need a enum GUC with more options. */
#define MAX_ENUM_OPTIONS 6
/*
* API for disabling error capture ereport(ERROR,..) by PGSM's error capture hook
* pgsm_emit_log_hook()
*
* Use these macros as follows:
* PGSM_DISABLE_ERROR_CAPUTRE();
* {
* ... code that might throw ereport(ERROR) ...
* }PGSM_END_DISABLE_ERROR_CAPTURE();
*
* These macros can be used to error recursion if the error gets
* thrown from within the function called from pgsm_emit_log_hook()
*/
extern volatile bool __pgsm_do_not_capture_error;
#define PGSM_DISABLE_ERROR_CAPUTRE() \
do { \
@@ -119,6 +132,27 @@ extern volatile bool __pgsm_do_not_capture_error;
#define PGSM_ERROR_CAPTURE_ENABLED \
__pgsm_do_not_capture_error == false
/*
* pg_stat_monitor uses the hash structure to store all query statistics
* except the query text, which gets stored out of line in the raw DSA area.
* Enabling USE_DYNAMIC_HASH uses the dshash for storing the query statistics
* that get created in the DSA area and can grow to any size.
*
* The only issue with using the dshash is that the newly created hash entries
* are explicitly locked by dshash, and its caller is required to release the lock.
* That works well as long as we do not want to swallow the errors thrown from
* dshash function. Since the lightweight locks acquired internally by dshash
* automatically get released by error.
* But throwing an error from pg_stat_monitor would mean erroring out the user query,
* which is not acceptable for any stat collector extension.
*
* Moreover, some of the pg_stat_monitor functions perform the sequence scan on the
* hash table, while the sequence scan support for dshash table is only available
* for PG 15 and onwards.
* So until we figure out the way to release the locks acquired internally by dshash
* in case of an error while ignoring the error at the same time, we will keep using
* the classic shared memory hash table.
*/
#ifdef USE_DYNAMIC_HASH
#define PGSM_HASH_TABLE dshash_table
#define PGSM_HASH_TABLE_HANDLE dshash_table_handle
@@ -355,28 +389,23 @@ typedef struct pgssSharedState
TimestampTz bucket_start_time[MAX_BUCKETS]; /* start time of the bucket */
LWLock *errors_lock; /* protects errors hashtable
* search/modification */
/*
* These variables are used when pgsm_overflow_target is ON.
*
* overflow is set to true when the query buffer overflows.
*
* n_bucket_cycles counts the number of times we changed bucket since the
* query buffer overflowed. When it reaches pgsm_max_buckets we remove the
* dump file, also reset the counter.
*
* This allows us to avoid having a large file on disk that would also
* slowdown queries to the pg_stat_monitor view.
*/
size_t n_bucket_cycles;
int hash_tranche_id;
void *raw_dsa_area;
void *raw_dsa_area; /* DSA area pointer to store query texts.
* dshash also lives in this memory when
* USE_DYNAMIC_HASH is enabled */
PGSM_HASH_TABLE_HANDLE hash_handle;
/* hash table handle. can be either
* classic shared memory hash or dshash
* (if we are using USE_DYNAMIC_HASH)
*/
} pgssSharedState;
typedef struct pgsmLocalState
{
pgssSharedState *shared_pgssState;
dsa_area *dsa;
dsa_area *dsa; /* local dsa area for backend attached to the
* dsa area created by postmaster at startup.
*/
PGSM_HASH_TABLE *shared_hash;
}pgsmLocalState;